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The Common Marmoset (Callithrix jacchus) Has Two Very Similar Semenogelin Genes as the Result of Gene Conversion¹

University Hospital MAS,³ Division of Clinical Chemistry, Department of Laboratory Medicine, Lund University, S-205 02 Malmö, Sweden Division of Evolutionary Molecular Systematics,⁴ Department of Cell and Organism Biology, Lund University, S-223 62 Lund, Sweden Department of Reproductive Biology,⁵ German Primate Center, Göttingen D-37077, Germany

ABSTRACT

The semen coagulum proteins have undergone substantial structural changes during evolution. In primates, these seminal vesicle-secreted proteins are known as semenogelin I (SEMG1) and semenogelin II (SEMG2). Previous studies on the common marmoset (Callithrix jacchus) showed that ejaculated semen from this New World monkey contains semenogelin, but it remained unclear whether it carries both genes or only SEMG1 and no SEMG2, like the closely related cotton-top tamarin (Saguinus oedipus). In this study we show that there are two genes, both expressed in the seminal vesicles. Surprisingly, the genes show an almost perfect sequence identity in a region of 1.25 kb, encompassing nearly half of the genes and containing exon 1, intron 1, and the first 0.9 kb of exon 2. The underlying molecular mechanism is most likely gene conversion, and a phylogenetic analysis suggests that SEMG1 is the most probable donor gene. The marmoset SEMG1 in this report differs from a previously reported cDNA by a lack of nucleotides encoding one repeat of 60 amino acids, suggesting that marmoset SEMG1 displays allelic size variation. This is similar to what was recently demonstrated in humans, but in marmosets the polymorphism was generated by a repeat duplication, whereas in humans it was a deletion. Together, these studies shed new light on the evolution of semenogelins and the mechanisms that have generated the structural diversity of semen coagulum proteins.

epididymis, male reproductive tract, seminal vesicles, sperm, sperm motility and transport

¹Supported by a grant from the Medical Faculty at Lund University and from MAS Cancer.

Correspondence: ²Camilla Valtonen-André, Wallenberg Laboratory, University Hospital MAS, S-205 02 Malmö, Sweden. FAX: 46 4033 7043; e-mail: C.Valtonen-Andre{at}med.lu.se