Membrane-Mediated Regulation of Sperm Fertilization Potential in Poultry

Abstract

Fertilization requires successful completion of molecular events taking place at different spatiotemporal scales. Transcriptionally and translationally inactive sperm need to rely on pre-assembled pathways modulated by extracellular signals that traverse the plasma membranes. However, species differences in how sperm respond to them delay the progress toward a comprehensive understanding of how activation of the signaling cascades is coordinated in poultry sperm. In chickens, recent studies have found that membrane rafts are present on the sperm surface and play important roles in regulating multistage fertilization. In this review, we focus on three steps in which membrane alteration plays a key role. The first is post-testicular maturation, in which bird sperm acquire fertilization functions through biochemical changes. The second part of this review concerns membrane regulation of sperm-egg binding and the acrosome reaction. Finally, we extend our discussion to the translation of membrane raft theory into a technical principle for the commercial production and genetic preservation of poultry.

Keywords: acrosome reaction; membrane rafts; signaling pathway; sperm; sterol.

Fig. 1.

Organization of membrane rafts in chicken sperm. G_M1 and sterols were labeled with Alexa 488-conjugated cholera toxin B subunit (CTB) and filipin (A and B). The plasma membrane overlying sperm head has specific membrane domains. Bright field (C). Bars=10 µm.

Fig. 2.

Detection of acrosome-reacted sperm. Acrosome reaction in chicken sperm was visualized by labelling with FITC-conjugated peanut aggulutinin (A). White arrows indicate AR. Merged image (B). Bars=10 µm.

Fig. 3.

The distribution of sterols in chicken sperm. Fresh and cryopreserved (Cryo) sperm were labelled with filipin (A and B). 22-(N(-7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino)-23,24-bisnor-5-cholen-3β-ol (NBD-cholesterol) was loaded into the plasma membrane of fresh chicken sperm (C). Bright field (D). Bars=10 µm.