Identification of the major rabbit and guinea pig semen coagulum proteins and description of the diversity of the REST gene locus in the mammalian clade Glires.

Åke Lundwall,Karin Hansson,Magnus Jonsson,Margareta Persson,Rajakumar Anbazhagan

doi:10.1371/journal.pone.0240607

Abstract

The seminal vesicle secretions of guinea pig and rabbit were analyzed for semen coagulum proteins. Using SDS-PAGE we discovered a previously not fully recognized semen coagulum protein, Svp5, in the guinea pig and a single predominant component, SVP200, in the rabbit. Potential genes of these proteins were identified in genome databases by their homology with human and murine genes. The structure of their fullength transcripts was determined using seminal vesicle cDNA and sequencing primers based on genomic sequences. Homology searching indicated that both Svp5 and SVP200 were synthesized from composite genes that were the result of merger between two genes showing homology with human SEMG2 and PI3. For a deeper understanding of the evolution of the genes, we retrieved and analyzed genome sequences from the REST gene loci, encompassing genes of semen coagulum proteins and related rapidly evolving seminal vesicle-transcribed genes, of 14 rodents and 2 lagomorphs. The analysis showed that rodents of the suborders myomorpha, hystricomorpha, and castorimorpha had unique sets of REST genes, whereas sciuromorpha seemed to be lacking such genes. It also indicated a closer relationship between myomorpha and castorimorpha than to rodents of the two other analyzed suborders. In the lagomorph species, the pika appeared to be devoid of REST genes, whereas the rabbit had a single expressed REST gene, SVP200, and two pseudogenes. The structural similarity of semen coagulum proteins in rabbit and hystricomph species suggests that they are closely related. This was also supported by other similarities at their REST gene loci, e.g. the finding of a PI3-like gene in the rabbit that also had features in common with caltrin2 of hystricomorph rodents. The homologies indicate that hystricomorpha may have separated from myomorpha and castorimorpha before the separation of hystricomorpha from lagomorpha.

Highlights

The semen of male mammals is formed at ejaculation by the mixing of spermatozoa-rich epididymal fluid with secretions from accessory sex glands
The rabbit seminal vesicle tissue was filled with a semisolid mass, assumed to consist of seminal vesicle secretion (SVS), which was solubilized by the high pH/urea buffer
The myomorph rodents carried 6 REST genes with close similarity to mouse Svs2-Svs6; the hystricomorph rodents carried 3 REST genes with close similarity to guinea pig Svp1, Svp2, and Svp5; in the kangaroo rat, a castorimorph rodent, we identified 4 previously not described REST genes based on their similarity to human semenogelin 2 (SEMG2); the ground squirrel, a sciuromorph rodent, carried a pseudogene homologous with human SEMG2, but no functional REST gene

Summary

Introduction

The semen of male mammals is formed at ejaculation by the mixing of spermatozoa-rich epididymal fluid with secretions from accessory sex glands. The newly ejaculated semen appears as a coagulum of varying consistency, which may subsequently liquefy within minutes, as in humans [1], or become stabilized and develop into a post copulatory vaginal plug following mating, as in some rodents [2]. Studies on the molecular properties of these proteins, and components related to them, have shown that there are two homologous coagulum proteins, denoted semenogelin 1 (SEMG1) and semenogelin 2 (SEMG2), in semen of humans and many primates [1, 5]. In the SVS of rat and mouse, there are 6 major proteins, denoted Svs1-Svs, of which Svs1-Svs are reported to be coagulum proteins, with Svs as the predominating component [4, 6, 7]. The guinea pig seminal vesicles are reported to yield 4 protein components from two major transcripts, one of which generates Svp2 [8], while the other transcript generates a polyprotein precursor of 43 kDa, which is processed to three secreted components; the major coagulum protein Svp and the overlapping and almost identical Svp and Svp4 [9]

Methods

Results

Discussion

Conclusion