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Dev Biol January 1, 2022; 487 10-20.
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Evo-Devo of Urbilateria and its larval forms.

De Robertis EM , Tejeda-Muñoz N .

Developmental biology has contributed greatly to evolutionary biology in the past century. With the discovery that vertebrates share Hox genes with Drosophila in 1984, it became apparent that all animals evolved from variations of an ancestral embryonic patterning genetic tool-kit. In the dorsal-ventral (D-V) axis, a fundamental experiment was the Spemann-Mangold organizer transplant performed in 1924. Almost a century later, D-V genes have been subjected to saturating molecular screens in Xenopus and extensive genetic screens in zebrafish. A network of secreted growth factor antagonists has emerged, and we review here in detail the Chordin/Tolloid/BMP pathway. Chordin establishes a morphogen gradient spanning the entire embryo that was present even in the cnidarian Nematostella. This ancient system was present in Urbilateria, the last common ancestor of the protostome and deuterostome bilateral animals. We suggest that Urbilateria had a complex life cycle with an adult benthic form on the sea bottom, and also a primary larval pelagic or planktonic phase to disperse the species in the marine milieu. Larvae with two rows of cilia beating in opposite directions to entrap food particles, an apical sensory organ, and a rudimentary eye, are present in many protostome and deuterostome phyla. Although the larval phase has been lost multiple times in evolution, and larvae can adopt traits present in their adult forms, the simplest explanation is that Urbilateria had a pelago-benthic life cycle. The use of conserved developmental patterning systems likely placed evolutionary constraints in the animal forms that evolved by natural selection.

PubMed ID: 35443190
Article link: Dev Biol

Species referenced: Xenopus laevis
Genes referenced: admp angptl4 bambi bmp1 bmp2 bmper cdx2 cer1 chrd.1 dkk1 frzb frzb2 fst gsc id3 kit lhx1 msx1 nodal nog pkdcc.1 pnhd ptprk rnf2 sox2 szl tbx3 tll1 twsg1 wnt8a XB5848002 [provisional] znrf3
GO keywords: embryonic pattern specification [+]

Article Images: [+] show captions