Rapidly evolving zona pellucida domain proteins are a major component of the vitelline envelope of abalone eggs

doi:10.1073/pnas.0603125103

Rapidly evolving zona pellucida domain proteins are a major component of the vitelline envelope of abalone eggs

Department of Genome Sciences, University of Washington, Box 357730, Seattle, WA 98195

Edited by Paul Wassarman, Mount Sinai School of Medicine, New York, NY, and accepted by the Editorial Board September 22, 2006 (received for review April 17, 2006)

Abstract

Proteins harboring a zona pellucida (ZP) domain are prominent components of vertebrate egg coats. Although less well characterized, the egg coat of the non-vertebrate marine gastropod abalone (Haliotis spp.) is also known to contain a ZP domain protein, raising the possibility of a common molecular basis of metazoan egg coat structures. Egg coat proteins from vertebrate as well as non-vertebrate taxa have been shown to evolve under positive selection. Studied most extensively in the abalone system, coevolution between adaptively diverging egg coat and sperm proteins may contribute to the rapid development of reproductive isolation. Thus, identifying the pattern of evolution among egg coat proteins is important in understanding the role these genes may play in the speciation process. The purpose of the present study is to characterize the constituent proteins of the egg coat [vitelline envelope (VE)] of abalone eggs and to provide preliminary evidence regarding how selection has acted on VE proteins during abalone evolution. A proteomic approach is used to match tandem mass spectra of peptides from purified VE proteins with abalone ovary EST sequences, identifying 9 of 10 ZP domain proteins as components of the VE. Maximum likelihood models of codon evolution suggest positive selection has acted among a subset of amino acids for 6 of these genes. This work provides further evidence of the prominence of ZP proteins as constituents of the egg coat, as well as the prominent role of positive selection in diversification of these reproductive proteins.

Footnotes

*To whom correspondence should be addressed. E-mail: jaagaard{at}gs.washington.edu
Author contributions: J.E.A., M.J.M., and W.J.S. designed research; J.E.A. performed research; X.Y. contributed new reagents/analytic tools; J.E.A., X.Y., and M.J.M. analyzed data; and J.E.A. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS direct submission. P.W. is a guest editor invited by the Editorial Board.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. DQ453710–DQ453752).
Abbreviations:

ZP,

zona pellucida;

VE,

vitelline envelope;

MS/MS,

tandem mass spectrometry;

VERL,

vitelline envelope receptor of lysin.