Developmental Biology - Lecture 5 Patterning the Vertebrate Body: Animal Models

A set of vocabulary flashcards covering axis formation, segmentation, Hox genes, vertebrate body plan, and key amphibian and avian development concepts from the lecture.

Anterior-posterior axis (A/P axis)

Head-to-tail axis along which body patterning occurs, established by maternal and zygotic genes.

Dorsal-ventral axis (D/V axis)

Back-to-belly axis patterned by Toll/Dorsal pathway and Dpp signaling.

Maternal genes

Genes provided in the oocyte that establish early body axes before zygotic transcription.

Zygotic genes

Genes expressed after fertilization; include gap, pair-rule, segmentation, and selector/homeotic genes.

Gap genes

Zygotic genes that subdivide the embryo into broad anterior-posterior domains.

Pair-rule genes

Zygotic genes that generate alternating stripes to refine segmentation.

Segmentation genes

Group of genes (including gap and pair-rule) that organize segments along the A/P axis.

Engrailed (En)

Transcription factor expressed at the anterior boundary of each parasegment; marks compartment boundaries.

Parasegment boundary

Boundary between adjacent parasegments, precursor to final segments.

Hedgehog signaling (Hh)

Secreted ligand signaling pathway that patterns neighboring cells and interacts with Patched.

Wingless signaling (Wg/Wnt)

Secreted Wnt ligand signaling through Frizzled receptor; helps maintain hh/en expression.

Patched

Receptor for Hedgehog; inhibits Smoothened in the absence of Hh.

Frizzled

Receptor for Wingless/Wnt signaling.

Parasegment

A repeating developmental unit in Drosophila segmentation defined by gene expression.

Segment

Final, matured body unit formed from parasegments.

Hox genes

Family of homeobox-containing transcription factors specifying segment identity along the A/P axis.

Homeobox

A ~60 amino acid DNA-binding domain found in Hox and other transcription factors.

Colinearity

Correspondence between gene order in Hox clusters and their spatial/temporal expression along the A/P axis.

Antennapedia complex (ANT-C)

Drosophila Hox cluster controlling anterior segment identities.

Bithorax complex (BX-C)

Drosophila Hox cluster controlling posterior segment identities.

Ubx (Ultrabithorax)

BX-C Hox gene specifying posterior thoracic/abdominal identities.

abd-A (abdominal-A)

BX-C Hox gene specifying abdominal identities.

Abd-B (Abdominal-B)

BX-C Hox gene specifying the most posterior identities.

Antp (Antennapedia)

ANT-C Hox gene; gain-of-function transforms antennae into legs.

Dfd (Deformed)

ANT-C Hox gene involved in cephalic segment identity.

Lab (Labial)

ANT-C Hox gene; contributes to head/thoracic identity.

pb (proboscipedia)

ANT-C Hox gene involved in mouthpart identity.

Homeotic transformation

Change in segment identity due to mutations in Hox genes.

Phylotypic stage

Developmental stage when embryos of different vertebrates look morphologically similar.

Vertebral column

Segmented backbone surrounding the spinal cord that defines the A/P axis.

Animal-vegetal axis (Xenopus eggs)

Polarity of Xenopus eggs with animal (pigmented) and vegetal (yolk-rich) hemispheres.

Cleavage

Rapid mitotic divisions of the zygote without growth, producing smaller cells.

Blastomere

A cell produced by cleavage divisions.

Blastula

Early embryo with a blastocoel cavity; spherical mass of cells.

Blastocoel

Fluid-filled cavity inside the blastula.

Gastrulation

Process forming germ layers via cell movements; includes involution and epiboly.

Involution

Inward movement of a cell sheet during gastrulation.

Epiboly

Expansion of cell layers to envelop the embryo.

Archenteron

Primitive gut formed during gastrulation.

Neurulation

Formation of the neural tube from neural folds.

Neural tube

Embryonic precursor to the brain and spinal cord.

Neural crest

Multipotent cells that migrate to form diverse tissues.

Xenopus laevis

African clawed frog; a common amphibian model in development.

Xenopus egg polarity

Animal and vegetal poles with distinct pigmentation and yolk distribution.

Cleavage in Xenopus

Early rapid divisions with little growth; cells become smaller (synchronous).

Chicken blastoderm

Flat, multi-cellular embryo present before gastrulation.

Albumen

Egg white; nutrients for the developing embryo.

Shell

Eggshell; allows gas exchange and protects the embryo in terrestrial environments.