vital dyes
relatively nontoxic synthetic dyes that can be used to label living cells
fate map
a representation of which parts of an embryo will give rise to various parts of the adult body
syncytium
a single cell containing several nuclei
cellularization
the process in which cell walls are formed between the nuclei in a syncytium
bicoid
a transcription factor that is concentrated in the presumptive anterior end of the embryo and directs formation of the head
nanos
a transcription factor that is concentrated in the presumptive posterior end of the embryo
maternal polarity genes
a class of genes provided by the mother such that their products are unevenly distributed in the zygote and thereby specify the anterior-posterior axis
hunchback
a transcription factor that is one of the class of gap genes that is inhibited by the nanos protein
gap genes
genes that encode a class of transcription factors, the expression of which is regulated by maternal polarity genes
pair-rule genes
genes that encode a class of transcription factors, the expression of which is regulated by gap genes
segment polarity genes
genes that encode a class of signaling factors, the expression of which is regulated by pair-rule genes
homeotic selector genes or Hox genes
also called simply ‘homeotic genes.’ a class of genes in which mutations tend to result in swapping out one body part for another, as when mutation of Antennapedia results in the formation of legs where antennae normally form
Antennapedia
a Hox gene in which mutations result in the formation of a leg where an antenna normally forms
halteres
paired structures that serve as counterweights to maintain balance in the flight of some flies
bithorax
a Hox gene in which mutations can result in the doubling of the thorax in Drosophila
Ultrabithorax
a Hox gene complex that affects the fate of cells in the thorax of Drosophila
homeobox
a nucleotide sequence that produces a DNA-binding domain in many transcription factor proteins. It is found in Hox genes and many other transcription factors
realizator genes
a class of genes, the expression of which is controlled by Hox genes, that direct the actual construction of particular body parts
colinearity
the property of Hox genes in which their order on the chromosome matches the order in which they are expressed along the anterior-posterior axis of the body
gene duplication and divergence
the evolutionary process by which a gene duplication is followed by successive divergence in the sequence and function of the two copies
prosencephalon
also called ‘forebrain.’ the most anterior aspect of the embryonic vertebrate brain. it will develop into the telencephalon and diencephalon
mesencephalon
also called ‘midbrain.’ the middle segment of the embryonic vertebrate brain. it will develop into the adult midbrain
rhombencephalon
also called ‘hindbrain.’ the caudal-most segment of the embryonic vertebrate brain. it will develop into the metencephalon (pons and cerebellum) and myelencephalon (medulla)
telencephalon
the anterior-most portion of the vertebrate brain, consisting of the cerebral cortex and related subcortical structures such as the basal ganglia and hippocampus
diencephalon
the portion of the vertebrate brain that consists of the thalamus and hypothalamus
pons
the portion of the brainstem caudal to the midbrain, to which the cerebellum is attached
cerebellum
a brain region attached to the pons that plays an important role in coordination of movement
metencephalon
a subdivision of the hindbrain that includes the cerebellum and the pons
myelencephalon
also called ‘medulla.’ the caudal-most portion of the vertebrate brainstem, which blends into the rostral spinal cord
Otx2
a homeobox gene required for the development of the vertebrate midbrain and forebrain
fibroblast growth factors (FGFs)
a family of proteins that act upon a family of receptor tyrosine kinase (RTK) receptors. they are concentrated in the posterior portions of the developing vertebrate nervous system and demarcate the midbrain/hindbrain junction
Emx2
a homeobox gene highly expressed in the posterior portion of the developing vertebrate cortex
Pax6
a homeobox gene highly expressed in the anterior portion of the developing vertebrate cortex
rhombomeres
a group of prominently segmented portions of the embryonic rhombencephalon
ephrins
a family of membrane-bound signaling molecules that bind to ephrin receptors, which are part of the receptor tyrosine kinase (RTK) superfamily
spontaneous abortion
the accidental loss of an embryo, sometimes called a miscarriage
rostral
referring to the head end
caudal
referring to the tail end
mitogen
a substance that promotes mitosis
Frizzled
a cell surface receptor protein that responds to Wnt
Wnt
a gene that encodes the secreted protein Wnt, which is concentrated in the posterior end of vertebrate embryos
retinoic acid (RA)
a steroid-like molecule, concentrated in the posterior end of vertebrate embryos, that promotes development of posterior structures. it is a powerful teratogen
retinoic acid receptor (RAR)
a member of the steroid receptor superfamily that serves as a receptor for retinoic acid
retinoic acid response element (RARE)
a specific sequence of DNA nucleotides that is bound by the retinoic acid-retinoic acid receptor complex, thereby regulating expression of the associated gene
teratogen
a substance that causes malformations in development
notochord
an embryonic rod-shaped structure that is derived from mesodermal tissue in all vertebrates and that induces formation of the ventral neural tube above
motor neurons
neurons that send axons out to the periphery to innervate and control muscles
signal peptide
a particular sequence of N-terminal amino acids that directs the full protein to the cell’s secretory pathway
Sonic hedgehog (Shh)
a gene that encodes the signaling protein that is secreted by the notochord and induces formation of the floor plate and the differentiation of motor neurons in the vertebrate neural tube
floor plate
the ventral portion of the vertebrate neural tube, the developing spinal cord
roof plate
the dorsal portion of the vertebrate neural tube