Early metazoan development module

A top-level developmental module that organises the conserved early events of animal (metazoan) embryogenesis into an ordered set of sub-programs, from the fertilised egg to a patterned, three-germ-layer embryo with a segregated germline. The trunk is a temporal sequence of four sub-programs, each detailed in its own dedicated module document: (1) the maternal-to-zygotic transition, which hands control from maternal factors to the embryo's own genome; (2) body axis specification, which converts graded morphogens into the AP, DV, and LR body axes; (3) germ layer specification during gastrulation, which partitions the embryo into endoderm, mesoderm, and ectoderm; and (4) primordial germ cell specification, which sets aside the gamete lineage. All four are wired by a small, deeply conserved "developmental toolkit" of signalling pathways - Wnt, TGF-beta/Nodal/BMP, Hedgehog, Notch, and RTK/FGF - captured here as a cross-cutting variant set that points to the existing signalling module documents. Grounded in GO:0009790 (embryo development).

This umbrella intentionally keeps each sub-program as a thin node that names its concept, exemplar regulators, and the dedicated module file that expands it, rather than duplicating the full decomposition. The sub-programs overlap in time and share machinery (e.g. the same Nodal/Wnt/BMP gradients pattern the axes AND specify germ layers), which is why the toolkit is factored out as a cross-cutting variant set. Exemplar accessions are curated human UniProt ids used only to orient conserved, pan-metazoan roles.