Bilateria gut evolution report

Geoff Read at
Thu Jan 4 18:18:49 EST 2001

Also in Nature this week is a very interesting piece of research examining 
gene expression in Platynereis dumerilii larvae and comparing it to prior 
research on deuterostome tornaria and auricularia larvae. If I understand 
correctly it looks like deuterostomy (blastopore gives rise to anus only, not 
anus & mouth) postdates the evolution of larval tube-shaped  guts with 2 

Arendt, D., U. Technau, & J. Wittbrodt. 2001. Evolution of the bilaterian larval 
foregut [Letter]. — Nature 409(6816):81 - 85.

"Bilateria are subdivided into Protostomia and Deuterostomia. Indirect 
development through primary, ciliary larvae occurs in both of these 
branches; however, the closing blastopore develops into mouth and anus in 
Protostomia and into anus only in Deuterostomia. Because of this important 
difference in larval gut ontogeny, the tube-shaped guts in protostome and 
deuterostome primary larvae are thought to have evolved independently. To 
test this hypothesis, we have analysed the expression of brachyury, otx 
and goosecoid homologues in the polychaete Platynereis dumerilii, which 
develops by means of a trochophora larva-the primary, ciliary larva 
prototypic for Protostomia. Here we show that brachyury expression in the 
ventral portion of the developing foregut in Platynereis and also otx 
expression along ciliated bands in the mouth region of the trochophora 
larva parallels expression in primary larvae in Deuterostomia. In addition, 
goosecoid expression in the foregut of Platynereis mirrors the function in 
higher Deuterostomia. We present molecular evidence for the evolutionary 
conservation of larval foreguts and mouth regions of Protostomia and 
Deuterostomia. Our data indicate that Urbilateria, the common bilaterian 
ancestors, developed through a primary, ciliary larva that already 
possessed a tripartite tube-shaped gut."

  Geoff Read < at>

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