PARENT SESSION

(35) COMPLEXIN 1 KNOCKOUT MOUSE SPERM ARE SUB-INFERTILE DUE TO A DEFECT IN ACROSOMAL EXOCYTOSIS.

Zhao, Longmei¹, Burkin, Heather¹, Reim, Kerstin², Brose, Nils², Miller, David¹, ¹ University of Illinois at Urbana-Champaign, Urbana, IL² Max-Plank-Institute for Experimental Medicine, Göttingen, Germany

ABSTRACT- Upon adhesion to the zona pellucida, mammalian sperm undergo regulated exocytosis of the acrosome. The acrosome reaction is necessary for sperm to penetrate the zona pellucida and fertilize an oocyte. Despite the difference in size, secretion dynamics and vesicle morphology, some parallels can be drawn between the sperm acrosome reaction and synaptic vesicle exocytosis. During both events, increased cytosolic calcium and the formation of a highly stable protein complex known as the SNARE complex appear important for membrane fusion and exocytosis. Complexin 1 in neurons is a cytosolic protein that binds tightly to the assembled SNARE complex and promotes exocytosis. Here we investigated the function of complexin 1 in acrosomal exocytosis. Complexin 1 was found in the acrosomal region of mammalian sperm and complexin antibodies inhibited the mouse sperm acrosome reaction in a dose dependent manner. Cell fractionation experiments demonstrated that complexins are mainly in the sperm cytosol. Complexin 1 bound sperm SNARE proteins in GST pulldown experiments. Additional studies were of complexin 1 null mice that develop severe ataxia and do not mate. Seminiferous tubules from these mice were morphologically normal and their cauda epididymal sperm had normal number, morphology and only small differences in motility, as assessed by computer assisted semen analysis. The chlortetracycline fluorescence assay results suggested that complexin 1 null sperm capacitated normally. An equal number of sperm from wild type and complexin 1 null sperm bound to the zona pellucida. Although complexin 1 null sperm acrosome reacted in response to A23187, they did not acrosome react in response to soluble zona pellucida proteins. Sperm from complexin 1 null mice had reduced fertilizing ability, as assessed by in vitro fertilization. Therefore complexin 1 is necessary for acrosomal exocytosis and normal fertility.

KEY WORDS: acrosome reaction, fertilization, SNARE, zona pellucida