A voltage-gated ion channel expressed specifically in spermatozoa

Calcium ions play a primary role in the regulation of sperm cell behavior. We report finding a voltage-gated ion channel (CatSper2) that is expressed in male germ cells but not in other cells. The putative channel contains 6 transmembrane segments, making it more similar to the voltage-gated potassi um channels, but the ion selectivity pore domain sequence resembles that of a Ca-v channel. The mRNA is expressed during the meiotic or post-meiotic s tages of spermatogenesis, and the protein is localized to the sperm flagell um, suggesting a role in the regulation of sperm motility. The mRNA for the channel is present in mouse, rat, and human sperm cells, and the gene is f ound on chromosome 2 E5-F1 in the mouse and 15q13 in the human. Recently, a nother voltage-gated channel (CatSper) that has features similar to the one reported here was discovered. It also is expressed within the flagellum an d is required for normal fertility of mice. However, expression of CatSper2 alone or coexpression with CatSper in cultured cells, or attempts to coimm unoprecipitate the two proteins from germ cells failed to demonstrate that these two unique but similar alpha -like subunits form either a homo- or he terotetramer. It is possible, therefore, that two independent a subunits, d ifferent from other known voltage-gated channels, regulate sperm motility.