Developmental Biology BIOL 3090: Patterning the Vertebrate Body — Axis Formation (Vocabulary Flashcards)

Vocabulary flashcards covering key terms and definitions from the lecture notes on axis formation, early embryonic development in Xenopus, chick, mouse, and human.

Epiblast

The remaining blastoderm that forms the embryo.

Hypoblast

Layer of cells forming the floor of the blastocyst cavity; contributes to extra-embryonic membranes.

Gastrulation

Process starting with the formation of the primitive streak that establishes germ layers.

Primitive streak

Embryonic structure where cells ingress during gastrulation; marks germ layer formation.

Ingression

Movement of individual cells inward through the primitive streak rather than as a sheet.

Cleavage

Early rapid cell divisions of an embryo without overall growth.

Morula

Solid ball of cells formed during cleavage.

Blastocyst

Early embryo stage with inner cell mass and trophectoderm.

Inner cell mass (ICM)

Cluster of cells in the blastocyst that forms the embryo and some extra-embryonic tissues.

Trophectoderm

Outer cells of the blastocyst that form extra-embryonic structures.

Notochord

Rod-like mesodermal signaling center forming anterior to the regressing node.

Hensen's node

Signaling center in the chick embryo; equivalent to the Spemann organizer.

Spemann organizer

Dorsalizing organizer region that patterns the embryo; equivalent to Hensen's node in chicks.

Neural tube

Structure formed by fusion of neural folds; becomes the central nervous system.

Neurulation

Process by which the neural tube forms from the neural plate.

Ectoderm

Germ layer that forms the skin and nervous system.

Mesoderm

Germ layer that forms muscle, bone, blood, and the notochord.

Endoderm

Germ layer that forms the gut lining and associated organs.

Extra-embryonic membranes

Chorion, amnion, yolk sac, and allantois; support embryonic development.

Chorion

Outer extra-embryonic membrane involved in exchange with maternal blood.

Amnion

Membrane surrounding the embryo that forms the amniotic cavity.

Allantois

Extraembryonic membrane for gas exchange and waste storage.

Yolk sac

Early nutrient source; part of the extra-embryonic membranes.

Primitive endoderm

Endodermal layer contributing to extra-embryonic membranes.

Cup-shaped embryo

Rodent (mouse) early embryo morphology; humans and birds have flatter early embryos.

Node (mammalian organizer)

Organizing center that patterns the body axis in mammals, analogous to Spemann organizer.

Dorsal determinants

Maternal factors that specify the dorsal axis (e.g., in Xenopus).

Sperm entry defines dorsal side

In Xenopus, the site of sperm entry helps set the future dorsal axis after cortical rotation.

Cortical rotation

Rotation of the cortex after fertilization that relocates determinants to the future dorsal side.

Wnt signaling pathway

Signaling pathway that promotes dorsal fates; involves stabilization of downstream effectors like beta-catenin.

Beta-catenin

Protein with dorsalizing effects when enriched on the dorsal side; initially maternally distributed and often degraded unless stabilized.

PMZ (posterior marginal zone)

Region in the chick blastoderm involved in establishing the posterior axis.

Gravity defines chick AP axis

Gravity and yolk orientation influence anterior-posterior axis formation in the chick embryo.

Somite stage

Developmental stage defined by the number of somites (e.g., 13-, 22-, 40-somite stages).

Amniocentesis

Sampling of amniotic fluid for fetal genetic testing, usually around 14–20 weeks.

Placenta

Structure in the uterine wall where maternal and embryonic blood exchange nutrients and wastes.

Monozygotic twins

Twins derived from a single zygote; identical twins formed by splitting of the embryo.

Amniotic cavity

Fluid-filled cavity surrounded by the amnion that protects and cushions the embryo.