A K(+)-selective CNG channel orchestrates Ca(2+) signalling in zebrafish sperm

Elife. 2015 Dec 9:4:e07624. doi: 10.7554/eLife.07624.

Abstract

Calcium in the flagellum controls sperm navigation. In sperm of marine invertebrates and mammals, Ca(2+) signalling has been intensely studied, whereas for fish little is known. In sea urchin sperm, a cyclic nucleotide-gated K(+) channel (CNGK) mediates a cGMP-induced hyperpolarization that evokes Ca(2+) influx. Here, we identify in sperm of the freshwater fish Danio rerio a novel CNGK family member featuring non-canonical properties. It is located in the sperm head rather than the flagellum and is controlled by intracellular pH, but not cyclic nucleotides. Alkalization hyperpolarizes sperm and produces Ca(2+) entry. Ca(2+) induces spinning-like swimming, different from swimming of sperm from other species. The "spinning" mode probably guides sperm into the micropyle, a narrow entrance on the surface of fish eggs. A picture is emerging of sperm channel orthologues that employ different activation mechanisms and serve different functions. The channel inventories probably reflect adaptations to species-specific challenges during fertilization.

Keywords: biophysics; cell biology; fertilization; potassium channel; sperm signalling; structural biology; zebrafish.

MeSH terms

  • Animals
  • Calcium Signaling*
  • Cyclic Nucleotide-Gated Cation Channels / metabolism*
  • Male
  • Potassium / metabolism*
  • Spermatozoa / drug effects
  • Spermatozoa / physiology*
  • Zebrafish / physiology*

Substances

  • Cyclic Nucleotide-Gated Cation Channels
  • Potassium

Grants and funding

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.