Submitted July 26, 2007
Returned for revision August 29, 2007
Accepted November 7, 2007
Minireview
Phylogenetic Analysis and Identification of Pseudogenes Reveal a Progressive Loss of Zona Pellucida Genes During Evolution of Vertebrates
Ghylène Goudet *,
Sylvie Mugnier ,
Isabelle Callebaut ,
and
Philippe Monget
* To whom correspondence should be addressed. E-mail: goudet{at}tours.inra.fr.
Abstract
Vertebrate eggs are surrounded by an extracellular matrix with similar functions and conserved individual components: the zona pellucida (ZP) glycoproteins. In mammals, chicken, frog and some fish species, we established an updated list of the ZP genes, we studied the relationships within the ZP gene family by using phylogenetic analysis, and we identified ZP pseudogenes. Our study confirmed the classification of ZP genes in six subfamilies: ZPA/ZP2, ZPB/ZP4, ZPC/ZP3, ZP1, ZPAX and ZPD. The identification of a Zpb pseudogene in the mouse genome, Zp1 pseudogenes in the dog and bovine genome, and Zpax pseudogenes in the human, chimpanzee, macaque and bovine genome showed that the evolution of ZP genes mainly occurs by death of genes. Our study revealed that the extracellular matrix surrounded vertebrate eggs contains three to at least six ZP glycoproteins. Mammals can be classified in three categories. In the mouse, the ZP is composed of three ZP proteins (ZPA/ZP2, ZPC/ZP3 and ZP1). In dog, cattle, and putatively pig, cat and rabbit, the zona is composed of three ZP proteins (ZPA/ZP2, ZPB/ZP4 and ZPC/ZP3). In human, chimpanzee, macaque and rat, the ZP is composed of four ZP proteins (ZPA/ZP2, ZPB/ZP4, ZPC/ZP3 and ZP1). Our review provides new directions to investigate the molecular basis of sperm-egg recognition, a mechanism which is not yet elucidated.
Key words:
Gamete Biology •
Fertilization •
Oocyte development •
Ovum •
zona pellucida
