Expression of Crisp-1 mRNA splice variants in the rat epididymis, and comparative analysis of the rat and mouse Crisp-1 gene regulatory regions

The rat Crisp-1 gene encodes Protein DE (acidic epididymal glycoprotein; AE G), a glycoprotein secreted by the epididymal epithelium that associates wi th maturing sperm and has been implicated in the process of sperm-egg fusio n. Previous characterization of the Crisp-1 messenger RNA in the rat epidid ymis has demonstrated the presence of 3 splice Variants (Klemme et al, 1999 ). This study was undertaken to determine if expression of the Crisp-1 spli ce Variants in the rat epididymis is region-specific and correlates with th e region-specific pattern of synthesis of the D and E forms of the Crisp-1 protein. Expression of each of the splice variants was shown by RNase prote ction assays to be under the control of androgens, but they are not differe ntially regulated either within the epididymal segments or along the length of the organ. The reported structure of the mouse Crisp-1 gene does not in clude an exon that is equivalent to the rat exon 1, suggesting that the rat splice Variants cannot exist in the mouse and may be specific to the rat. Furthermore, the mouse transcription start site is situated in a different region of the gene than in the rat. In this study, a comparison of the mous e and rat genes in the region flanking the mouse exon 1 and the rat exon 2 (within the rat intron 1) shows greater than 80% sequence identity, includi ng the conservation of several putative androgen receptor binding sites. In addition, the rat gene is shown to have a corrupted TATA box in intron 1 t hat corresponds to the TATA box located in the mouse gene. These observatio ns explain the preferential transcription for the mouse gene in this region , while the predominant start site for the rat gene is 5' of the upstream e xon 1. Although an exon corresponding to the rat exon 1 has not been found in the mouse gene, reverse transcription-polymerase chain reaction experime nts using mouse epididymal RNA suggest that such an exon exists in the mous e gene and is transcribed at low frequency.