Identification of Rat Cysteine-Rich Secretory Protein 4 (Crisp4) as the Ortholog to Human CRISP1 and Mouse Crisp4

Abstract

Cysteine-rich secretory proteins (CRISPs) are present in a diverse population of organisms and are defined by 16 conserved cysteine residues spanning a plant pathogenesis related-1 and a C-terminal cysteine-rich domain. To date, the diversification of mammalian CRISPs is evidenced by the existence of two, three, and four paralogous genes in the rat, human, and mouse, respectively. The current study identifies a third rat Crisp paralog we term Crisp4. The gene for Crisp4 is on rat chromosome 9 within 1 Mb of both the Crisp1 and Crisp2 genes. The full-length transcript for this gene was cloned from rat epididymal RNA and encodes a protein that shares 69% and 91% similarity with human CRISP1 and mouse CRISP4, respectively. Expression of rat Crisp4 is most abundant in the epididymis, with the highest levels of transcription observed in the caput and corpus epididymis. In contrast, rat CRISP4 protein is most abundant in the corpus and cauda regions of the epididymis. Rat CRISP4 protein is also present in caudal sperm extracts, appearing as a detergent-soluble form at the predicted MWR (26 kDa). Our data identify rat Crisp4 as the true ortholog to human CRISP1 and mouse Crisp4, and demonstrate its interaction with spermatozoa in the epididymis.

Cysteine‐rich secretory proteins are not exclusively expressed in the male reproductive tract

“…Epididymosomes are transport vesicles involved in the transfer of epididymal proteins onto sperm (Sullivan et al, 2007). In accordance with the mRNA expression reported by Nolan et al (2006), CRISP1 staining intensity increased in a proximal to distal direction (Fig. 3B,C).…”

“…In the human, these genes are found in chromosome 6. Based on sequence homology, mouse Crisp1 appears to be a duplication of Crisp3, and Crisp4 is the mouse orthologue of human CRISP1 (Nolan et al, 2006).…”

“…It has been suggested that CRISP3 (and indeed other CRISPs) may have a role in innate immunity by virtue of their presence in exocrine secretions, e.g., in saliva and tears, and in immune cells, e.g., in pre-B lymphocytes and neutrophils (Haendler et al, 1993(Haendler et al, , 1999Kjeldsen et al, 1996;Kratzschmar et al, 1996;Pfisterer et al, 1996). CRISP4 was only recently identified and it was at this time that the extent of confusion in naming between species became clear (Jalkanen et al, 2005;Nolan et al, 2006). Published data to date suggest that Crisp4 was almost exclusively produced in the epididymis under androgen control.…”

“…Published data to date suggest that Crisp4 was almost exclusively produced in the epididymis under androgen control. Within both the mouse and rat epididymis, Crisp4 is expressed more proximally, i.e., primarily within the caput and corpus, whereas Crisp1 is expressed in distal segments, i.e., corpus and cauda (Nolan et al, 2006). Similar to CRISP1, CRISP4 is secreted by epididymal principal cells and attaches loosely to maturing sperm (Nolan et al, 2006).…”

“…Within both the mouse and rat epididymis, Crisp4 is expressed more proximally, i.e., primarily within the caput and corpus, whereas Crisp1 is expressed in distal segments, i.e., corpus and cauda (Nolan et al, 2006). Similar to CRISP1, CRISP4 is secreted by epididymal principal cells and attaches loosely to maturing sperm (Nolan et al, 2006). The function of mouse CRISP4 is unknown, but based on its loose membrane association and 42% identity to CRISP1 it may act as a decapacitation factor.…”