Amino acid sequence analysis showed that Bin1b corresponds to SPAG11 variant E.
The amplification of the predicted SPAG11 variant C transcript by RTPCR has been also reported in the rat and mouse epididymis.
Interestingly, Bin1b was not expressed in any other major organs, such as the lung or kidney, except the epididymis.64) RTPCR examination showed that hBD-4, hBD-5, hBD6, and SPAG11 variant D were expressed predominantly in the human epididymis (Table 1).
SPAG11 variant E expression was also most prominent in the caput region, but a comparable level of expression was detected in the corpus region.
In humans, the former group includes SPAG11 variant D, hBD-4, hBD-5, and hBD-6, and the latter group includes hBD-1, hBD-2, and hBD-3.
Immunostaining for SPAG11 family proteins indicated the binding of SPAG11 to the sperm head, suggesting a possible role in sperm maturation.61) Furthermore, Zhou et al.