Acetyl Choline-A neurotransmitter involved in Alzheimer's disease.
Acrosome-Cell region covering the sperm head that contains enzymes, which disintegrate the egg coating and allow the sperm to penetrate the egg
Action potential -- An electrical signal conducted down the axon by way of sodium and potassium ions moving in and out of the neuron.
Adult stem cell ­ An undifferentiated cell found in a differentiated tissue, regardless of the age of the donor, that can renew itself and (with certain limitations) differentiate to yield all the specialized cell types of the tissue from which it originated.
Adult neurogenesis - The formation of new neurons after an individual has reached maturity. Previously thought to be rare or impossible.
Allogeneic transplant-Transplant using tissue or cells from a donor individual not genetically identical to the patient.
Alzheimer's Disease-A neurodegenerative disorder that results in the slow loss of mental functionsing.
Amino acid-Substance essential to formation of protein
Amnion-Flat-celled, extraembryonic membrane, attached around margin of epiblast; Derived from epiblast (ectoderm) of bilaminar embryo, it later joins with chorion and surrounds umbilical cord
Androgen - General term for any male sex hormone in vertebrates
Angioblasts-Cells in mesoderm that create primitive blood vessels
Apical ectodermal ridge--Ectodermal thickening at tip of developing limp bud which appears 25-30 days after fertilization and disappears 40-42 days after fertilization; Region of limb bud that organizes limb development
Aromatase - An enzyme which converts androgens to estrogens by desaturating ring a of the steroid.
Assisted Reproductive Technology (ART) ­ Any fertility treatments or procedures that include laboratory handling of eggs or embryos, such as in vitro fertilization (IVF).
Autoimmune diseases--A constellation of different diseases all characterized by the failure of the body to distinguish "self" from "non-self" causing the body to attack its own tissues.
Astrocyte- a glial cell that provides nutrients and other substances for neurons of the CNS.
Autologous transplant ­ Transplant using tissue from the same individual, or a twinas the intended recipient of the transplant. Such a transplant helps avoid complications of immune rejection.
Basal Ganglia-A an area in the center of the brain that is responsible for control of movement.
Basal layer-Lower layer of fetal epidermis conceptus
Bilaminar embryo-Embryo approximately 11-16 days after fertilization has two layers: the epiblast (future ectoderm) below amniotic cavity and the hypoblast (future endoderm) above yolk sac
Bilaminar embryonic disc-Disc composed of epiblast and hypoblast sac
Blastocoel ­ The cavity in the blastula of the developing embryo.
Blastocyst ­ A preimplantation embryo (about 5 days in humans) of 30-150 cells. The blastocyst consists of a sphere made up of an outer layer of cells (the trophectoderm), a fluid-filled cavity (the blastocoel), and a cluster of cells on the interior (the inner cell mass). The inner cell mass gives rise to what will become the fetus. At the time of implantation the mouse blastocyst is made up of about 70 trophoblast cells and 30 ICM cells.
Blastomeres-Cells produced by cleavage of zygote
Blastula ­ An early stage in the development of an ovum consisting of a hollow sphere of cells enclosing the blastocoel. Also called a blastocyst (see above).
Bone marrow ­ The soft, living tissue that fills most bone cavities and contains hematopoietic stem cells, from which all red and white blood cells develop. The bone marrow also contains mesenchymal stem cells that a number of cell types' come from, including chondrocytes, which produce cartilage.
Bone marrow stem cell (BMSC) ­ One of at least two types of multipotent stem cells: hematopoietic stem cell and mesenchymal stem cell.
Bone marrow transplantation­ Transplantation of bone marrow from one individual to another. Autologous bone marrow transplantation is a process in which a patient's bone marrow is withdrawn and preserved, then injected back into the patient to restore the production of healthy blood and immune cells by the bone marrow. This strategy is often used in patients with certain types of cancer who have undergone radiation therapy or chemotherapy that destroys the bone marrow cells.
Brain plate-Rostral part of neural plate sac
Brain vesicles-Primary divisions of embryonic brain sac
Cannula- A tube that serves as a guiding channel for electrodes, needles, etc.
Caudal-Towards the tail region of the embryo
Cavitation ­ A process that occurs during the formation of the blastocyst and establishes
Cell adhesion-Joining of cell surfaces often mediated by specific cell adhesion molecules (CAM's)
Cell cycle ­ The orderly sequence of events by which the cell duplicates its contents and divides into two. Cell division is regulated by numerous molecular signals, each dependent on the other.
Cell lines- Cultures of disaggregated tissue that can be maintained and propagated for use in research. The length of time cells will survive in culture varies. Some cell lines are immortalized; that is, they can be maintained essentially indefinitely, for one of a variety of reasons. Embryonic stem cells and embryonic germ cells are immortal because they express telomerase, one of the factors necessary for cells to propagate normally.
Centrifuge-A device that spins test tubes really fast to separate cells from a liquid medium. The cells, which are more dense, sink to the bottom.
Cephalic-Situated near or pertaining to embryo's head region
Cerebellum-Hindbrain structure (below and behind the cerebrum) consisting of two lateral lobes and a central lobe; Helps coordinate voluntary motor movements, posture and balance
Cerebral cortex- the outermost layer of the brain
Cerebral hemispheres-Left and right halves of the brain
Chromosomes ­ Nucleic acid-protein structures in the nucleus of a cell. Chromosomes contain the DNA, the carrier of hereditary information, and thus the genes. Genes are working sub-units of DNA that carry the genetic code for specific proteins, interspersed with large amounts of DNA of unknown function. A normal human body cell contains 46 chromosomes; a normal human gamete, 23 chromosomes.
Cleavage ­ The process of cell division in the very early embryo before it becomes a blastocyst.
Cleavage pattern ­ The pattern in which cells in a very early embryo divide; each species of organism displays a characteristic cleavage pattern which can be observed under a microscope; departure from the characteristic cleavage pattern usually indicates that an embryo is abnormal, and therefore cleavage pattern is used as a criterion for preimplantation screening of embryos
Clinical trial-Research to test the safety and efficacy of new treatments or to compare the effects of different treatments in patients or healthy volunteers.
Clone ­ 1) an exact genetic replica of a DNA molecule, cell, tissue, organ, or an entire plant or animal. 2) an organism having the same nuclear genome as another organism.
Cloning ­ The production of a clone. (for the purpose of this meeting, creating an individual animal, or person that derives its nuclear genes from a diploid cell taken from an embryo, fetus, or born individual of the same species).
Computerized tomography(CT) scan- Use of a computer to analyze data obtained from a scanning beam of X-rays.
Conception-Fertilization; When the egg and spermatozoon merge; Beginning of pregnancy
containing numerous structures, known as organelles, that carry out essential cell functions.
Convolutions-Irregular folds on brain surface
Cortical reaction-Reaction of the oocyte's cortex which preventing penetration by more than one spermatozoon
Cranial-Toward head region of embryo
Cryopreservation-The process of freezing biological materials in such a way that they can be stored for long periods of time, then thawed for use.
Craniostomy- surgical procedure of drilling or cutting open the skull
Culture ­ This is the process of growing cells or embryos in a laboratory.
Cytokines- a generic term used for signalling molecules released by cells. Sort of like hormones.
Cytoplasm ­ The contents of a cell other than the nucleus. Cytoplasm consists of a fluid
Depression-A psycholoical illness that results in the lack of emotions and feelings of tiredness. May be caused by neurodegeneration.
Diencephalon-More posterior of two portions of forebrain; Identifiable approximately twenty-one days after fertilization, it later develops into thalamus, subthalamus and hypothalamus
Differentiation-Change of cell morphology and/or metabolism to provide specialized functions
Differentiation- the process of cell division and development that gives rise to different types of cells
Diploid ­ A cell or tissue having two chromosome sets, as opposed to the haploid situation of gametes, which have only one chromosome set.
DNA ­ Deoxyribonucleic acid, found primarily in the nucleus of cells (some DNA is also found in the mitochondrion). DNA is the genetic material that carries the genes and thus the instructions for making all the structures and materials the body needs to function.
Dopamine-A neurotransmitter, secreted by the substania nigra.
Donor Insemination (DI) or Artificial Insemination Donor (AID) ­ depositing sperm from a male donor inside a female reproductive tract for the purpose of achieving pregnancy.
Dura mater- the outermost layer of tissue that encases the CNS
Ectoderm-Embryonic tissue layer primarily responsible for development of nervous system and skin
Ectopic pregnancy-Pregnancy that develops in an abnormal location (i.e., outside of uterus)
Ectopic tissue-Tissue that has formed abnormally temporally or spatially.
Embryonic germ cells-These cells are found in a specific part of the embryo/fetus called the gonadal ridge, and normally develop into mature gametes.
Embryo ­ 1) the earliest stage of development, from the single cell to the completion of implantation in the uterus. 2) a group of cells arising from the egg that has the potential to develop into a complete organism. In medical terms, the word "embryo" usually refers to the developing human from fertilization up to 8 weeks, when the beginnings of the major organ systems have been established.
Embryo splitting ­ When an early stage embryo is separated into two or more embryos with identical genetic makeup, essentially creating identical twins or higher multiples.
Embryoblast-Inner cell mass which gives rise to the embryo and its attached membranes
Embryoid bodies (EBs) ­ Clumps of cellular structures that arise when embryonic stem cells are cultured. Embryoid bodies contain tissue from all three of the germ layers: endoderm, mesoderm, and ectoderm. Embryoid bodies are not part of normal development and occur only in in-vitro conditions.
Embryonic carcinoma (EC) cells ­ A type of pluripotent stem cell derived from teratocarcinoma (usually a testis tumor).
Embryonic disk ­ A group of cells derived from the inner cell mass of the blastocyst, which later develops into an embryo. The disc initially contains two cell layers, but after gastrulation consists of three germ layers known as the endoderm, mesoderm, and ectoderm.
Embryonic endoderm-Embryonic germ layer that forms epithelium of embryonic gut and its derivatives
Embryonic germ (EG) cells ­ Pluripotent stem cell lines derived from the primitive germline cells that migrate, during early development, to the future gonads to form the progenitors of egg or sperm cells. Their properties are similar to those of ES cells, but there may be differences while they are migrating to the gonads due to changes in DNA methylation that occur in the germline of the cells.
Embryonic mesoderm-Embryonic mesoderm appears at gastrulation and forms somites, intermediate mesoderm (nephrotome), and lateral plate mesoderm (somatopleure and splanchnopleure); Appears after extraembryonic mesoderm
Embryonic stem (ES) cell lines ­ Populations of dividing cells established from embryonic stem cells and cultured in the laboratory. Within embryonic cell lines are cells that can produce more embryonic stem cells, or under conditions of differentiation, give rise to collections of cells that include most, if not all cell types that can be found in a postimplantation embryo, fetus, or developed organism, but not trophoblast or placenta. To date no embryonic stem cells cultured in vitro can give rise to developed organisms or even developed organs.
Embryonic stem (ES) cells ­ Primitive (undifferentiated) cultured cells from the embryo that have the potential to become a wide variety of specialized cell types, that is, are pluripotent. They are derived from the inner cell mass of the blastocyst stage of development.
Endoderm ­ Definitive endoderm is one of the three germ layers formed during gastrulation; it gives rise to organs such as the lungs and digestive organs. The primitive endoderm is the lower layer of the blastocyst that gives rise to fetal membranes.
Enucleation ­ This is a process whereby the nuclear material of a cell is removed, leaving only the cytoplasm. When applied to an egg, the removal of the maternal chromosomes, which are not surrounded by a nuclear membrane.
Epiblast ­ Gives rise to the ectoderm, mesoderm, and definitive endoderm. The mesoderm displaces the hypoblast cells and forms the definitive endodermal cell layer on the inner surface of the embryonic disk.
Epidermis--Outermost layer of skin derived from surface ectoderm
Epilepsy-A disese cause by overactivity in the brain. Its main symptom is seizures
Estradiol - A hormone synthesized primarily in the ovaries, but also in the testes and elsewhere in small amounts. Like estrogen it regulates female sexual characteristics as well as behaviors.
Estrogen - In humans, oestrogen is formed in the ovary, possibly the adrenal cortex, the testis and the foetoplacental unit. It is responsible for the development of the female secondary sex characteristics and during the menstrual cycle it acts on the female genitalia to produce an environment suitable for the fertilization, implantation and nutrition of the early embryo.
Enzyme - A protein molecule produced by living organisms that catalyses (speeds up) chemical reactions of other substances without itself being destroyed or altered upon completion of the reactions. That is what differentiates it from substrates or products, both of which change as a result of the reaction.
Ex vivo ­ Outside the living body.
Extraembryonic mesoderm-Outermost layer of mesoderm, which forms chorion, amnion, yolk sac, and allantois
Extraembryonic structures-Structures that are derivatives of zygote but not part of embryo; Consist of extraembryonic membranes and umbilical cord
Extraembryonic tissues ­ Intrauterine tissues that support the embryo's placenta, umbilical cord, and amniotic sac.
Fertilization-Union of male and female gametes; Process, also known as conception, involves sperm capacitation, acrosome reaction with penetration of ovum, attachment of sperm head to secondary oocyte, and fusion of male and female pronuclei
Fetus ­ 1) Legally, the developing organism from the completion of implantation in the uterus up to the time of birth. 2) In medical terms, refers to the developing human from 8 weeks to birth. At 8 weeks the embryo is 2.0 ­3.0 cm long and weighs 1 ­ 4.5 g. The rudiments of the internal organs such as liver and kidney and limbs, fingers and toes have formed.
Fibroblast ­ Cells that give rise to connective tissue.
Flow cytometry- the process of identifying cells using a battery of antibodies for specific cell markers
Forebrain-Most forward part of three brain area; Includes cerebral cortex and limbic system and is also know as prosencephalon
Gamete ­ A haploid reproductive cell (i.e. egg or sperm), having only 23 chromosomes in the human.
Gastrula-Embryo in early stages of germ layer formation, immediately following blastula stage; Gastrula consists of two cell layers (ectoderm and endoderm) which enclosed archenteron (central cavity) that opens to outside via the blastopore
Gastrulation-Process in which post-blastula embryo forms three germ layers, which will differentiate into various structures and organs
Gene ­ A functional unit of heredity that is a segment of DNA located in a specific site on a chromosome. A gene directs the formation of an enzyme of other protein or RNA molecule.
Gene expression ­ The process by which proteins and occasionally RNAs are made from the instructions encoded in genes. Alterations in gene expression change the function of the cell, tissue, organ or whole organism, and sometimes result in observable characteristics associated with a particular gene.
Gene therapy-The use of genetic material, usually DNA, to correct inherited or accumulated genetic damage.
Genome ­ The complete genetic material of an organism.
Germline cells; Germ cell ­ Cells comprising actual reproductive components of an organism (specifically, eggs and sperm, and their precursors).
Gestation ­ The period of development of an organism from fertilization of the ovum until birth.
Glia- the supporting cells if the CNS
Globus Pallidus-An area of the Basal ganglia that makes an inhibatory output to motor contorl on the thalmus.
Graft-versus-host disease­ A condition that occurs following bone marrow transplantation in which the donor-derived T cells attack the host's tissues.
Growth factor- chemicals in the body that direct cell growth and development
Haploid ­ Refers to a gamete having one chromosome set, as opposed to the diploid situation of somatic cells or tissues, where there are two chromosome sets.
Hematopoiesis ­ Generation of blood cells, mainly in the bone marrow.
Hematopoietic cell transplantation ­ Transplantation of cells with blood-forming potential, usually bone marrow. Hematopoietic stem cells are the only cells that provide rapid and sustained reconstitution of blood formation. Hematopoietic stem cells are found in adult bone marrow, umbilical cord blood, fetal liver, and mobilized peripheral blood (the nucleated cell fraction of blood after treatment of the donor with agents that increase the passage of hematopoietic stem cells from bone marrow to blood).
Hematopoietic stem cell/Hemocytoblasts ­Primordial cells capable of developing into any type of blood cell
Hepatic ­ Relating to the liver.
Hepatocyte ­ Liver cell.
Hindbrain-Most posterior part of brain including pons, medulla and cerebellum
Hippocampus - a complex curved structure of the cerebral cortex forming the floor of the inferior horn of the lateral ventricle. Involved in memory formation.
Hormone -- any one of a number of biochemical substances, usually combining protein and lipids, that are produced by a certain cell or tissue and that cause a specific biological change or activity to occur in another cell or tissue located elsewhere in the body. Generally function as blood-borne messengers that cause relatively slow changes in function.
Huntington's Disease-A movement disorder characterized by excessive movement.
HVC (HVc) - The High Vocal Center. In birds, an area of the brain that appears to control the neurogenesis associated with adult song learning and plasticity.
Hypoblast-Endoderm of embryo; Layer underlying epiblast
Identical twinning ­ See Monozygotic twining.
Immortal cell ­ A cell that is capable of an unlimited number of cell divisions, and is therefore, self-replenishing
Implantation ­ The process by which an embryo becomes attached to the inside of the uterus. (7-14 days in humans)
In utero ­ In the uterus.
In vitro fertilization (IVF) ­ An assisted reproduction technique in which fertilization is accomplished outside the body.
In vitro­ Literally, "in glass;" in a laboratory dish or test tube; an artificial environment.
In vivo ­ In the living subject; in a natural environment.
Informed consent ­ A process in which a patient gives written consent (agreement) to undergo a medical procedure after having been provided with information about the nature of the procedure, risks, potential benefits, alternatives, etc. by his/her doctor
Inner cell mass ­ The cluster of cells inside the blastocyst. These cells give rise to the embryonic disk of the later embryo and, ultimately, the fetus and amnion.
Intracytoplasmic Sperm Injection ­ An assisted reproductive method in which a sperm is injected directly into an unfertilized egg using a microscopic needle; this procedure is used in cases of severe male infertility.
Invagination-Pushing-in of a layer of cells, as in gastrulation or in formation of proctodeum
L-Dopa-A precursur of the neurotransmitter dopamine, it is used to treat Parkinson's disease.
Ligand- A molecule that binds to a receptor. This can include single amino acids, modified amino acids, peptides, and proteins.
Male infertility ­ Condition where male patient is infertile for reasons such as very low sperm count, sperm that cannot swim properly, or sperm that are unable to penetrate the egg
Meiosis ­ A process whereby cells divide to produce eggs, sperm, or other cells that contain half the number of chromosomes found in the somatic cells. During fertilization, the nuclei of the sperm and ovum fuse and produce a zygote with the full chromosome complements.
Melanoblasts-Neural crest derivatives that provide skin pigment
Mesectoderm-Mesenchymal cells derived from neural crest
Mesenchymal stem cells (MSCs) ­Self-renewing stromal cells from a variety of tissues that include in their progeny fibroblasts, bone osteocytes, fat cells, etc.
Mesenchyme-Cells derived from mesoderm, which are capable of developing into connective tissues, blood and lymphatic and blood vessels
Mesoderm ­ The middle germ layer of the embryonic disk, which consists of a population of cells give rise to bone, muscle, blood cells, and connective tissue.
Mesoderm-Embryonic tissue layer that develops into muscles, bones and circulatory system
Messenger RNA (mRNA)- a type of RNA that contains the information for the synthesis of a polypeptide.
Midbrain-Middle part of brain containing optic lobe; Responsible for hearing and sight
Mitochondrial heteroplasmy ­ Normally, mitochondria are inherited from the mother and are usually all of one genetic type. With cloning, a mixture of mitochondria from both the donor cell and recipient egg may result.
Mitochondrion ­ A cellular structure in the cytoplasm that provides energy to the cell. The mitochondrion contains 37 genes on a circular mitochondrial DNA, as compared with about 35,000 genes in the nuclear DNA.
Molecular marker- a segment of DNA that is found at a specific site in the genome and has properties that enable it to be uniquely recognized using molecular tools such as gel electrophoresis.
Monoclonal antibodies. Antibodies produced in the laboratory by specialized cells called hybridomas. The important features of these antibodies include their specificity of binding to a single antigen (protein), the ability to produce them in unlimited amounts, and their homogeneity. These antibodies have proven to be very useful in the detection of several diseases (including, but not limited to, cancer and various viral infections) and in therapy (for certain cancers).
Monozygotic twins ­ Twins derived from one egg and one sperm.
Morphogenesis-Study or process of normal development encompassing growth (size), differentiation (form), and pattern formation
Morula-The preimplantation embryo from the 2 cell to 32-cell stage (Day1 to Day 3 after fertilization in human). Individual cells are called blastomeres and they are loosely clustered together. At the 32-cell stage the cells adhere to each other more tightly and the morula becomes "compacted".
Multipotent stem cells ­ Stem cells whose progeny are of multiple differentiated cell types, but usually all within a particular tissue, organ, or physiological system. For example, blood-forming (hematopoietic) stem cells are single multipotent cells that can produce progeny that include HSC, blood cell-restricted oligopotent progenitors, and all cell types and elements (e.g., platelets) that are normal components of the blood.
Mutation ­ A change in DNA that alters a gene and thus the gene's product, leading in some cases to deformity or disease. Mutations can occur spontaneously during cell division or can be triggered by environmental stresses such as sunlight, radiation, and chemicals.
Myelencephalon-Posterior section of the hindbrain, including the medulla oblongata
Myelinization-Process of coating nerve fibers with myelin to form myelin sheath
Myelin-Soft, white fatty, protein-like substance produced by Schwann Cells that coats nerves (in a myelin sheath) to speed up nervous system transmission
Myotome-Portion of somite paraxial mesoderm (one of the three divisions of each somite) that forms skeletal muscles of trunk
Neural crest-Crest of neural fold; Formed by ectodermal cells that migrate lateral to neural tube between Stages 8 and 12)
Neural folds-Stages of neural tube formation; Paired folds arising from neural plate
Neural groove-Midline groove between the two neural folds
Neural plate-Ectodermal thickening in amniotic sac floor; Forerunner of nervous system (spinal cord and brain)
Neural plasticity- See plasticity
Neural tube-Ectodermal tube formed by union of two neural folds; Dorsal midline structure induced by notochord that forms brain in cranial region and spinal cord in more caudal regions
Neurodegenerative disorder-A disease that is caused by the death or injury of neurons.
Neurectoderm-Neural crest and neural tube derivatives
Neuroepithelial cells-Cells forming the walls of neural tube
Neuroglia-See Gliablasts
Neuromeres-Early metameric divisions of brain
Neurulation-Neural tube formation
NMDA - N methyl D aspartate. A type of neurotransmitter, general excitatory, involved in Long-Term Potentiation and learning.
Notochordal plate-Rod-like rostral extension from primitive streak, incorporated temporarily into endoderm
Notochordal process-Hollow rod extending rostrally from primitive node
Notochord-Cells that develop into backbone or vertebrae; Chordate characteristic that induces neural tube and persists as intervertebral discs
Nucleus ­ The core compartment of a cell that contains the chromosomes.
Oligodendrocyte- a type of glia that forms myelin sheaths around the axons of neurons
Oocyte ­ Developing egg; usually a large and immobile cell.
Ooplasmic Transfer ­ An assisted reproduction method that essentially enhances the defective (egg cytoplasm) from the patient's egg with healthy cytoplasm from a donor egg. This method may restore fertility to older women and women with genetically defective mitochondria. This procedure can be done in one of two ways ­ 1) The nucleus from the patient's egg is transferred into an enucleated donor egg, and then the egg is fertilized with sperm in vitro, or 2) Cytoplasm from a healthy donor egg is injected into the patient's egg along with sperm, which results in fertilization.
other body cells are called somatic cells.
Ovary - One of two small oval bodies situated on either side of the uterus on the posterior surface of the broad ligament. The structures in which the ova (eggs) are developed and released during ovulation.
Ovum-Egg or female reproductive cell
Paraxial mesoderm-Embryonic mesoderm alongside notochord; Undergoes segmentation to form somites
Parkinson's Disease-A movement disorder characterised by a lack of being able to move freely.
Pattern formation-Arrangement or topology of cells/tissues, such as thumb and little finger in limb bud.
Phenotype- the outward expression of a gene.
Placebo effect-when the patient believes he is recieving a treatment, but is not really getting one.
Placenta ­ The spongy structure in the uterus that is responsible for anchoring the fetus, fetomaternal gaseous and metabolic exchange and circulation of Mothers blood from which the fetus derives its nourishment and oxygen.
Plasticity ­ The ability of stem cells from one adult tissue to generate the differentiated types of another tissue. Also refers to any neuron's ability to change some aspects of its shape and composition to increase or decrease it's connection with other neurons.
Pluripotent stem cells (PSC) ­ Stem cells that include in their progeny all cell types that can be found in a postimplantation embryo, fetus, or developed organism, but not embryonic components of the trophoblast and placenta (these are usually called extra-embryonic).
Prechordal plate-Thickened endoderm rostral to notochordal process; becomes part of oral membrane
Precursor Cells ­ In fetal or adult tissues, these are partly differentiated cells that divide and give rise to differentiated cells. Also known as progenitor cells (see below).
Pre-implantation embryo ­ The very early, free-floating embryo, from the time the egg is fertilized until implantation in the mother's womb is complete. Also, fertilized eggs (zygotes) and products of somatic cell transfer into an empty egg and all of the developmental stages up to, but not beyond, the blastocyst stage.
Primary brain vesicles-The forebrain, midbrain and hindbrain vesicles
Primary germ layers ­ The three initial embryonic germ layers­endoderm, mesoderm, and ectoderm­from which all other somatic tissue-types develop.
Primitive groove (primitive pit, neurenteric canal)-Channel of cell migration for generating mesoderm at gastrulation
Primitive node-Elevation of primitive streak
Primitive streak- The initial band of cells running the length of embryo's back that initiates the development of the nervous system and spinal cord; Appears around Day 14 and initiates gastrulation and formation of germ layers The primitive streak establishes and reveals the embryo's head-tail and left-right orientations.
Primordial germline cells-The source of embryonic germ cells. In normal development, these are the cells that give rise to eggs or sperm.
Progenitor cells ­ Can differentiate into more than one type of mature cells, but lack the capacity to self-renew. Progenitor cells are derived from stem cells and are intermediate to the production of mature cells.
Recombinant DNA-Molecules that are constructed outside living cells by joining natural or synthetic DNA segments in such a way that they can replicate in a living cell (the replicative products are also considered to be recombinant DNA).
Ribonucleic acid (RNA) ­ A chemical that is similar in structure to DNA. One of its main functions is to translate the genetic code of DNA into structural proteins.
Ribosome ­ Any of the RNA- and protein-rich cytoplasmic organelles that are sites of protein synthesis.
Sclerotome-One of three subdivisions of a somite; Gives rise to vertebrae and ribs
Secondary neurulation-Formation of lower end of spinal cord from cells of neural cord
Segmentation-Formation of the somites from paraxial mesoderm
Soma- In a neuron, the soma is the cell body, the portion which contains most of the material that actually keeps it alive.
Somatic Cell Nuclear Transfer (SCNT) ­ Transferring the nucleus from a donor somatic cell to an unfertilized egg cell from which the maternal chromosomes have been removed.
Somatic cells ­ Any cell of a plant or animal other than a germ cell or germ cell precursor.
Somatic mesoderm-Mesoderm with embryonic origin on either side of the notochord; Develops into series of somites, mesenchymes and vertebral columns
Somites-Blocks of tissue on either side of embryo's spinal column that will develop into muscles and bones of head and trunk
Sperm/Spermatozoon­ Mature male reproductive cells.
Spinal column-Bones that protect spinal cord
Spinal cord-Part of nervous system, which regresses from tip of spinal column up until third lumbar vertebrae at time of birth
Spinal nerve-Nerve supplying the body and extremities; 32 pairs with dorsal (sensory) and ventral (motor) roots
Stem cells ­ Non- specialized cells that have the capacity to 1) self-renew and 2) differentiate to more mature cells.
Stereotaxic apparatus- a device that permits a surgeon to position an electrode or other device into a specific part of the brain.
Striatum-An area in the basal ganglia that is lost in Huntington's disease.
Stroke-Damage to the brain caused by a loss of blood flow to the brain and the corresonding loss of oxygen.
Subependymal cells- the cells adjacent and below the ventricles; source of neural stem cells
Substantia nigra-An area in the midbrain that secretes the neurotransmitter dopamine. It sends a major input to the Basal ganglia.
Subventricular zone- see subependymal cells
Surrogacy ­ A legal arrangement whereby a woman (the surrogate) agrees to become pregnant for another woman with the intention of surrendering the child at birth. There are two types of surrogacy ­ genetic (the surrogate has donated her egg to the pregnancy) and gestational (the surrogate has no genetic relationship to the fetus.)
Telomerase ­ An enzyme that is composed of a catalytic protein component and an RNA template and that synthesizes DNA at the ends of chromosomes.
Telomere ­ The end of a chromosome, associated with a characteristic DNA sequence that is replicated in a special way.
Testosterone - Male sex hormone (androgen) secreted by the interstitial cells of the testis of mammals and responsible for triggering the development of sperm and of many secondary sexual characteristics.
Thalamus-Major relay center of brain; Develops from lateral wall of diencephalon by Day 40
Tissue culture ­ Growth of tissue in vitro on an artificial nutrient medium for experimental research.
Totipotent cells ­ Have unlimited developmental capability. The totipotent cells of the very early embryo have the capacity to differentiate into extra embryonic membranes and tissues, the embryo, and all postembryonic tissues and organs.
Trait- any characteristic that an organism displays. Morphological traits affect the appearance of an organism. Physiological traits affect the ability of an organism to function. A third category of traits are those that affect an organism's behavior (behavioral traits).
Trans effect- an effect on gene expression that occurs even though two DNA segments are not physically adjacent to each other. Trans effects are mediated through diffusible genetic regulatory proteins.
Transcription ­ Making an RNA copy from a sequence of DNA (a gene). Transcription is the first step in gene expression.
Transcription factors- a broad category of proteins that influence the ability of RNA polymerase to transcribe DNA into RNA.
Transdifferentiation ­ The ability of a particular cell of one tissue, organ or system, including stem or progenitor cells, to differentiate into a cell type characteristic of another tissue, or organ.
Translation ­ The process of forming a protein molecule at a ribosomal site of protein synthesis from information contained in messenger RNA.
Trophectoderm ­ The outer layer of the developing blastocyst that will ultimately form the embryonic side of the placenta.
Trophoblast ­ The extraembryonic tissue responsible for negotiating implantation, developing into the placenta, and controlling the exchange of oxygen and metabolites between mother and embryo.
Undifferentiated ­ Not having changed to become a specialized cell type.
Unipotent stem cells ­ Stem cells that divide as well as give rise to a single mature cell type; e.g., spermatogenic stem cells.
Up-regulation- genetic regulation that leads to an increase in gene expression.
Vascular ­ Composed of, or having to do with, blood vessels.
Ventricle- fluid-filled chamber in the brain
Ventricular/subventricular zone - A thin strip of cells located around the ventricles of the brain. The site of neurogenesis throughout most organisms development and life cycle.
Yolk sac-First cavity of the developing embryo; Provides nourishment for embryo/fetus until its own circulary system is functioning
Zona pellucida ­ A thick, transparent noncellular layer that surrounds and protects the oocyte. Mucoprotein membrane that surrounds egg and is secreted by ovarian follicle cells
Zygote ­ A cell formed by the union of male and female germ cells (sperm and egg, respectively).
Zygotic gene- a gene that is expressed after fertilization.
Definitions compiled with references from:
Hale, W.G. and J.P. Margham (1991). The HarperCollins Dictionary of Biology. New York: HarperCollins.
Sadler, T.W. (1990). Langman's Medical Embryology (6th ed.). Philadelphia: Willams & Wilkins.
Webster's Encyclopedia Unabridged Dictionary of the English Language (1996). New York: Gramercy.
National Institute of Health's report "Stem Cells: Scientific Progress and Future Research Directions"
National Bioethics Advisory Committee (NBAC) report "Cloning Human
Beings."