Gamete Biology

HOXBES2: A Novel Epididymal HOXB2 Homeoprotein and Its Domain-Specific Association with Spermatozoa

Abstract
The sperm from the testis acquires complete fertilizing ability and forward progressive motility following its transit through the epididymis. Acquisition of these characteristics results from the modification of the sperm proteome following interactions with epididymal secretions. In our attempts to identify epididymis-specific sperm plasma membrane proteins, a partial 2.83 kb clone was identified by immunoscreening a monkey epididymal cDNA library with an agglutinating monoclonal antibody raised against washed human spermatozoa. The sequence of the 2.83 kb clone exhibited homology to the region between 1 and 1097 bp of the homeobox gene, Hoxb2. This sequence was found to be species conserved as revealed by RT-PCR analysis. To obtain full-length clone of the sequence, 5' RACE-PCR (rapid amplification of cDNA ends PCR) was carried out using rat epididymal RNA as the template. It resulted in a full-length 1.657 kb cDNA encoding a 32.9 kDa putative protein. The protein designated as HOXBES2 exhibited homology to the conserved 61 amino acid homeodomain region of the HOXB2 homeoprotein. However, characteristic differences were noted in its amino and carboxyl termini as compared to HOXB2. A putative 30 kDa protein was detected in the tissue extracts from adult rat epididymis and caudal spermatozoa and a 37 kDa protein in the rat embryo, when probed with a polyclonal antibody against HOXB2 protein. Multiple tissue Western blot and immunohistochemical analysis further indicated its expression in the cytoplasm of the principal and basal epithelial cells with maximal expression in the distal epididymal segments. Northern analysis detected a single ~2.5 kb transcript from the adult epididymis. Indirect immunofluorescence localized the protein to the acrosome, midpiece and equatorial segment of rat caudal and ejaculated human and monkey spermatozoa, respectively. In conclusion, we have identified and characterized a novel epididymal homeoprotein different from HOXB2 protein and hereinafter referred to as HOXBES2, (HOXB2 homeodomain containing Epididymis Specific Sperm protein) with a probable role in fertilization.

Key words: Epididymis • Gene regulation • Sperm • Sperm maturation • Testosterone

This article has been cited by other articles:

				E. Prabagaran, U. C. Hegde, S. B. Moodbidri, A. H. Bandivdekar, and V. P. Raghavan Postnatal Expression and Androgen Regulation of HOXBES2 Homeoprotein in Rat Epididymis J Androl, September 1, 2007; 28(5): 755 - 771. [Abstract] [Full Text] [PDF]