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
openings.
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 <g.read at niwa.cri.nz>
-- ANNELIDA LIST
Discuss = <annelida at net.bio.net> = talk to all members
Server = <biosci-server at net.bio.net> = un/subscribes
Archives = http://www.bio.net/hypermail/annelida/
Resources = http://biodiversity.uno.edu/~worms/annelid.html
--
