Evolution and human tissue expression of the Cres/Testatin subgroup genes, a reproductive tissue specific subgroup of the type 2 cystatins

Abstract

The cystatin family comprises a group of generally broadly expressed protease inhibitors. The Cres/Testatin subgroup (CTES) genes within the type 2 cystatins differs from the classical type 2 cystatins in having a strikingly reproductive tissue-specific expression, and putative functions in reproduction have therefore been discussed. We have performed evolutionary studies of the CTES genes based on gene searches in genomes from 11 species. Ancestors of the cystatin family can be traced back to plants. We have localized the evolutionary origin of the CTES genes to the split of marsupial and placental mammals. A model for the evolution of these genes illustrates that they constitute a dynamic group of genes, which has undergone several gene expansions and we find indications of a high degree of positive selection, in striking contrast to what is seen for the classical cystatin C. We show with phylogenetic relations that the CTES genes are clustered into three original groups, a testatin, a Cres, and a CstL1 group. We have further characterized the expression patterns of all human members of the subfamily. Of a total of nine identified human genes, four express putative functional transcripts with a predominant expression in the male reproductive system. Our results are compatible with a function of this gene family in reproduction.

Evolutionary analysis of the cystatin family in three Schistosoma species

“…In human, glycoproteins of the Cres/Testatin subgroup are expressed in reproductive tissues and their function may be related to reproduction (Frygelius et al, 2010). The topology of this subgroup showed in Figure 4 is consistent with the phylogeny reported by Frygelius et al (2010). Interestingly this subgroup lacks the consensus Q-x-V-x-G motif (Table 2 and Figure 3).…”

“…Figure 4 shows that these proteins have a common origin and may represent a new subgroup within I25 family. Phylogenetic and comparative analyses show that genes involved in reproduction as Cres/Testatin and host pathogen interaction are under strong positive selection (Frygelius et al, 2010). …”

“…Moreover, the secreted 125A protein was also found expressed in the prostate gland in the adult stage of F. gigantica , which suggests a regulative role of cysteine protease activity in reproductive system. Similarly, the expression of human cystatin I25B subgroup proteins, also called Cres/Testatin, was localized at the reproductive tissues and their function may be related to reproduction (Frygelius et al, 2010). Interestingly, human Cres/Testatin subgroup was placed in the same clade with the Schistosoma cystatins I25B (Figure 4).…”

Cystatin-related epididymal spermatogenic subgroup members are part of an amyloid matrix and associated with extracellular vesicles in the mouse epididymal lumen

“…Similar to CRES, CRES2, CRES3 and cystatin E2 are expressed by the principal cells in the mouse initial segment epididymal epithelium Li et al, 2003Li et al, , 2005. The human homologs of all CRES subgroup genes have been identified and the expression of four genes established, including CRES and CRES2 in the human testis and/or epididymis suggesting conserved functions in human reproduction (Wassler et al, 2002;Frygelius et al, 2010). However, except for studies showing that CRES2 and CRES3 are associated with human and mouse spermatozoa in the epididymis, respectively, little is known about the remaining CRES subgroup family members (Hamil et al, 2002;Li et al, 2005).…”

“…All eight CRES subgroup members are primarily expressed in the testis and/or epididymis implying specialized functions during spermatogenesis and epididymal sperm maturation (Cornwall et al, 1992;Frygelius et al, 2010). Subgroup members also lack consensus sites for cysteine protease inhibition suggesting their biological functions are likely distinct from the typical family 2 cystatins such as cystatin C. Indeed, CRES did not inhibit cysteine proteases in vitro but instead inhibited the serine proteases prohormone convertase 2 and prohormone convertase 4, suggesting a role in the regulation of proprotein processing Mishra et al, 2012).…”