Equatorin is not essential for acrosome biogenesis but is required for the acrosome reaction.
The acrosome is a specialized organelle that covers the anterior part of the sperm nucleus and plays an essential role in mammalian fertilization. However, the regulatory mechanisms controlling acrosome biogenesis and acrosome exocytosis during fertilization are largely unknown. Equatorin (Eqtn) is a membrane protein that is specifically localized to the acrosomal membrane. In the present study, the physiological functions of Eqtn were investigated using a gene knockout mouse model. We found that Eqtn(-/-) males were subfertile. Only approximately 50% of plugged females were pregnant after mating with Eqtn(-/-) males, whereas more than 90% of plugged females were pregnant after mating with control males. Sperm and acrosomes from Eqtn(-/-) mice presented normal motility and morphology. However, the fertilization and induced acrosome exocytosis rates of Eqtn-deficient sperm were dramatically reduced. Further studies revealed that the Eqtn protein might interact with Syntaxin1a and SNAP25, but loss of Eqtn did not affect the protein levels of these genes. Therefore, our study demonstrates that Eqtn is not essential for acrosome biogenesis but is required for the acrosome reaction. Eqtn is involved in the fusion of the outer acrosomal membrane and the sperm plasma membrane during the acrosome reaction, most likely via an interaction with the SNARE complex.
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China.
Jianxiu
J
Hao
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
Min
M
Chen
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China.
Shaoyang
S
Ji
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China.
Xiaona
X
Wang
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China.
Yanbo
Y
Wang
MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center of Nanjing University, Nanjing Biomedical Research Institute, National Resource Center for Mutant Mice, Nanjing 210061, China.
Xingxu
X
Huang
State Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
Lin
L
Yang
State Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
Yaqing
Y
Wang
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
Xiuhong
X
Cui
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
Limin
L
Lv
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China. Electronic address: liuyx@ioz.ac.cn.
Yixun
Y
Liu
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China. Electronic address: gaof@ioz.ac.cn.
Fei
F
Gao
D000177:Acrosome / Q000502:physiology* / Q000648:ultrastructure; D020101:Acrosome Reaction; D000818:Animals; D005260:Female; D005306:Fertilization; D055786:Gene Knockout Techniques; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism; D050827:Syntaxin 1 / Q000378:metabolism
C512717:Eqtn protein, mouse; D008565:Membrane Proteins; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1
Acrosome reaction; Eqtn; Male infertility; SNAREs