Sperm GIRK2-Containing K⁺ Inward Rectifying Channels Participate in Sperm Capacitation and Fertilization

Abstract

The GIRK2-containing inward-rectifying K⁺ ion channels have been implicated in mammalian spermatogenesis. While the Girk2 null mice are fertile, the male weaver transgenic mice carrying a gain-of-function mutation in the Girk2 gene are infertile. To establish the exact period of spermatogenesis affected by this mutation, we performed StaPut isolation and morphological characterization of the germ cells present in the weaver testis. Germ cells representing all periods of spermatogenesis were identified. However, no spermatozoa were present, suggesting that this mutation only affected the haploid phase of spermatogenesis. Real-time PCR studies performed on StaPut purified germ cells from wild-type mice indicated that the Girk2 transcripts were exclusively expressed in spermatids. Immunofluorescence studies of mouse and boar spermatids/spermatozoa localized the GIRK2 K⁺ containing channels to the acrosomal region of the sperm plasma membrane. During porcine in vitro fertilization (IVF), GIRK2-containing channels remained associated with the acrosomal shroud following zona-induced acrosome reaction. Fertilization was blocked by tertiapin-Q (TQ), a specific inhibitor of GIRK channels, and by anti-GIRK2 antibodies. Altogether, studies in two different mammalian species point to a conserved mechanism by which the GIRK2 inward-rectifying K⁺ ion channels support sperm function during fertilization.

Keywords:

• GIRK2
• in vitro fertilization
• mouse
• pig
• sperm

Acknowledgments

We thank Ms. Cheryl Jensen, Ms. Melainia McLain, and Mr. Randy Tindall (Electron Microscopy Core, University of Missouri) for EM sample processing, and Ms. Kathy Craighead for clerical assistance. Special thanks go to Ms. Doris Pitts and Ms. Kathy Craighead for preparing this manuscript for publication. We also gratefully acknowledge Dr. Peter MacLeish for reviewing the manuscript and the free loan of Guava instrument by IMV Technologies, Mineneapolis, MN.

Declaration of Interest: These studies were supported by grants HD41749 from National Institutes of Child Health and Human Development, Minority Biomedical Research support grant S06GM08248, and Research Centers in University Institutions grant RRA03034 to K.T. and W.T. Y-J Y was in part supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MEST) (No. 2010-0001356). In addition, this work was supported by funding from the Food for the 21st Century Program of the University of Missouri-Columbia, the USDA-CREES National Research Initiative Competitive Grant No. 2002-35203-12237 and National Research Initiative Competitive Grant No. 2007-35203-18274 from the USDA National Institute of Food and Agriculture, to P.S. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.