Meeting Abstract
47.1 Sunday, Jan. 5 10:15 Evolution of protostomy in the Brachiopoda MARTIN-DURAN, J.M.*; PASSAMANECK, Y.J.; MARTINDALE, M.Q.; HEJNOL, A.; Sars International Centre for Marine Molecular Biology, Univ. of Bergen, Norway; Kewalo Marine Laboratory, Univ. of Hawaii, Honolulu, HI; The Whitney Laboratory for Marine Bioscience, Univ. of Florida, FL; Sars International Centre for Marine Molecular Biology, Univ. of Bergen, Norway chema.martin@sars.uib.no
The blastopore, the orifice of endomesoderm invagination during gastrulation, can form the mouth (protostomy), the anus (deuterostomy), both gut openings (amphistomy), or none (blastopore closure) in bilaterians. The relationship between these openings was used to divide the Bilateria into the Deuterostomia and Protostomia, a split also supported by molecular phylogenies. However, there is a strikingly vast diversity of blastoporal fates within the Protostomia, even between closely related species. To understand the evolution of different gastrulation modes and cell fates in this group, we compared the development of a protostomic brachiopod (Terebratalia transversa) with that of a deuterostomic brachiopod (Novocrania anomala). In late blastula embryos, anterior/oral markers (six3/6, otx), posterior markers (cdx, evx) and endomesodermal genes (foxA, twi, GATA456) are radially expressed along the animal-vegetal axis in a similar pattern in both brachiopods. The blastopore is located at the vegetal pole, and initially posterior/anal markers are detected here in both species, as in deuterostome embryos. In N. anomala, the blastopore remains in the posterior region of the embryo, whereas in T. transversa, part of the blastopore moves anteriorly to meet animal oral ectoderm and form the mouth. It is the expression of anterior markers (six3/6, NK2.1, otx, gsc) in this region of the blastopore that represses the posterior markers, allowing the blastopore to move. Our data explains protostomy and amphistomy as gastrulation modes derived from an original deuterostomic condition, contrary to what most accepted theories about metazoan evolution propose.
