100. Which of the following statements in relation to cell movement during gastrulation
in Sea urchin is/are correct?
(A) Delamination leads to the formation of endoderm
(B) Ingression leads to the development of mesoderm
(C) Involution leads to the development of ectoderm
(D) Invagination leads to the development of endoderm

Options (A) and (B) are correct. Sea urchin gastrulation involves specific cell movements that form germ layers, with delamination contributing to endoderm and ingression producing mesoderm.​​

Option Analysis

Delamination and Endoderm (A): Delamination separates cells as sheets from the vegetal plate, primarily involving veg2-derived cells that form endoderm precursors during early archenteron stages.​​

Ingression and Mesoderm (B): Ingression sees primary mesenchyme cells (PMCs) from micromeres detach individually, enter the blastocoel via epithelial-mesenchymal transition, and develop into mesoderm for skeletogenesis.​

Involution and Ectoderm (C): Involution, rolling of cell sheets over the blastopore lip, does not occur prominently in sea urchins; ectoderm arises from mesomeres without this movement, making this incorrect.​

Invagination and Endoderm (D): Invagination buckles the vegetal plate to form the archenteron, driven by non-skeletogenic mesoderm (NSM) initially, with endoderm contributing to elongation—not primary formation—thus incorrect.​

Sea urchin gastrulation showcases precise cell movements like delamination, ingression, involution, and invagination that establish germ layers during embryogenesis. These processes transform the blastula into a gastrula, critical for CSIR NET life sciences studies in developmental biology.​

Key Cell Movements

• Ingression: Primary mesenchyme cells ingress from the vegetal plate into the blastocoel, forming mesoderm and larval skeleton via EMT.​

• Invagination: Vegetal plate bends to initiate archenteron; NSM drives primary phase, endoderm aids secondary elongation.​

• Delamination: Veg2-derived sheets separate to contribute endoderm, distinct from individual cell migrations.​​

• Involution: Minimal role; absent as dominant movement, unlike amphibians; ectoderm from mesomeres spreads via epiboly.​

Germ Layer Formation