Enkurin was identified initially in mouse sperm where it was suggested to act as an intracellular adaptor protein linking membrane calcium influx to intracellular signaling pathways. In order to examine the function of this protein, a targeted mutation was introduced into the mouse Enkurin gene. Males that were homozygous for this mutated allele were subfertile. This was associated with lower rates of sperm transport in the female reproductive tract, including reduced entry into the oviduct and slower migration to the site of fertilization in the distal oviduct, and with poor progressive motility in vitro. Flagella from wild-type animals exhibited symmetrical bending and progressive motility in culture medium, and demembranated flagella exhibited the “curlicue” response to Ca²⁺ in vitro. In contrast, flagella of mice homozygous for the mutated allele displayed only asymmetric bending, nonprogressive motility, and a loss of Ca²⁺-responsiveness following demembrantion. We propose that Enkurin is part of a flagellar Ca²⁺-sensor that regulates bending and that the motility defects following mutation of the locus are the proximate cause of subfertility.

Summary Sentence

The protein Enkurin is essential for control of flagellar bending and for sperm transport through the female reproductive tract.