† Present address: School of Earth and Environmental Sciences, University of Adelaide, SA 5005, Australia
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Evolution of yolk protein genes in the Echinodermata
Article first published online: 30 MAR 2012
© 2012 Wiley Periodicals, Inc.
Evolution & Development
Volume 14, Issue 2, pages 139–151, March / April 2012
How to Cite
Prowse, T. A. A. and Byrne, M. (2012), Evolution of yolk protein genes in the Echinodermata. Evolution & Development, 14: 139–151. doi: 10.1111/j.1525-142X.2012.00531.x
- Issue published online: 30 MAR 2012
- Article first published online: 30 MAR 2012
- Australian Research Council
Vitellogenin genes (vtg) encode large lipid transfer proteins (LLTPs) that are typically female-specific, functioning as precursors to major yolk proteins (MYPs). Within the phylum Echinodermata, however, the MYP of the Echinozoa (Echinoidea + Holothuroidea) is expressed by an unrelated transferrin-like gene that has a reproductive function in both sexes. We investigated egg proteins in the Asterozoa (Asteroidea + Ophiuroidea), a sister clade to the Echinozoa, showing that eggs of the asteroid Parvulastra exigua contain a vitellogenin protein (Vtg). vtg is expressed by P. exigua, a species with large eggs and nonfeeding larvae, and by the related asterinid Patiriella regularis which has small eggs and feeding larvae. In the Asteroidea, therefore, the reproductive function of vtg is conserved despite significant life history evolution. Like the echinozoan MYP gene, asteroid vtg is expressed in both sexes and may play a role in the development of both ovaries and testes. Phylogenetic analysis indicated that a putative Vtg from the sea urchin genome, a likely pseudogene, does not clade with asteroid Vtg. We propose the following sequence as a potential pathway for the evolution of YP genes in the Echinodermata: (1) the ancestral echinoderm produced YPs derived from Vtg, (2) bisexual vtg expression subsequently evolved in the echinoderm lineage, (3) the reproductive function of vtg was assumed by a transferrin-like gene in the ancestral echinozoan, and (4) redundant echinozoan vtg was released from stabilizing selection.