Cloning of Rainbow Trout Egg Envelope Proteins: Members of a Unique Group of Structural Proteins1

Abstract

All vertebrate eggs are surrounded by an extracellular envelope that protects the egg and is vital for a successful fertilization. The terminology and functions of the egg envelope vary in different vertebrate groups, but the envelope itself is consistently composed of a few major proteins that are deposited around the oocyte during oocyte growth. Here, we describe the deduced amino acid sequences and tissue expression patterns of the three major egg envelope proteins for rainbow trout (Oncorhynchus mykiss). All three vitelline envelope proteins (VEPs) are expressed in the livers of both male and female fish, with higher expression in females. In addition, VEPgamma mRNA is also detected in the female gonads. To our knowledge, this is the first time that expression of a VEP protein gene has been demonstrated to occur in more than one organ. Sequence comparison reveals that all three VEP proteins share distinct homology with their amphibian, avian, and mammalian counterparts. Whereas mammalian zona pellucida protein 3 isoforms contain two conserved serines needed for sperm binding, these are not conserved in teleost species, in which sperm entry is restricted to the micropyle. Besides the difference in VEPgamma sperm-binding function, the high sequence homology suggests that the egg envelope proteins from these distinct vertebrate groups share a common ancestry and form a unique group of structural proteins.

Ultrastructural studies of the morphological variations of the egg surface and envelopes of the African catfish <em>Clarias gariepinus</em> (Burchell, 1822) before and after fertilisation with a discussion of fertilisation mechanism

“…Hyllner et al (2001) concluded that the chorion proteins from the vertebrate groups of fishes and their amphibian, avian and mammalian counterparts share a common ancestry and form a unique group of structural proteins. Such proteins exhibit dramatic changes during chorion hardening.…”

Molecular characterization and expression pattern of three zona pellucida 3 genes in the Chinese sturgeon, Acipenser sinensis

“…In our study, all three AsZP3 s produced in the ovary also lack a C-terminus as well as other teleosts. In fact, fish ZP protein precursors can incorporate the egg coat without a C-terminus TMD (Sugiyama et al 1999;Hyllner et al 2001). So it seems that TMD region of fish ZP proteins does not appear to be needed for the assembly of ZP proteins that originate in the oocyte (Modig et al 2006).…”

“…For instance, medaka (Murata et al 1995), rainbow trout (Hyllner et al 2001), and gilthead seabream (Del Giacco et al 1998) synthesized ZP3 protein in liver, which is in contrast to chickens, mice, Xenopus, crucian carp, goldfish, common carp, and zebrafish. In chickens, synthesis occurs in granulose cells (Waclawek et al 1998); whereas in mouse, Xenopus, and crucian carp, it occurs in the oocyte (Fan et al 2001;Yamaguchi et al 1989;Waclawek et al 1998).…”

“…Since fish ZP3 cDNA molecules were first characterized in medaka, Oryzias latipes (Murata et al 1995), cDNA cloning and sequencing of ZP3 have been reported in a number of fish species, such as gilthead sea bream, Sparus aurata (Del Giacco et al 1998;Modig et al 2006), zebrafish, Danio rerio (Wang and Gong 1999;Del Giacco et al 2000), common carp, Cyprinus carpio (Chang et al 1996), gyno-crucian and gono-crucian carp (Fan et al 2001), rainbow trout, Oncorhynchus mykiss (Hyllner et al 2001), and half-smooth tongue sole, Cynoglossus semilaevis (Sun et al 2010). In recent years, based on available genome sequence and subtractive cDNA libraries, more ZP3 gene isoforms were characterized.…”

“…ZP proteins are synthesized mainly in the liver of some teleost species (Lyons et al 1993;Hamazaki et al 1989;Shimizu et al 1998;Kanamori et al 2003;Hyllner et al 2001) in contrast to chicken, gilthead seabream, mouse, Xenopus, carp, and zebrafish (Waclawek et al 1998;Epifano et al 1995;Yamaguchi et al 1989;Chang et al 1996Chang et al , 1997Wang and Gong 1999). In chicken, the synthesis occurs both in the granulosa cells (Waclawek et al 1998) and in the liver (Bausek et al 2000), whereas mouse, human (Epifano et al 1995;Wassarman et al 2004), and Xenopus (Yamaguchi et al 1989) synthesize ZP proteins in the oocytes.…”