A point mutation of aSNAP causes impaired acrosome reaction and reduced male fertility

BÁTIZ LF; DE BLAS GA; MICHAUT MA; RAMÍREZ AR; RODRÍGUEZ JF; RATTO MH; OLIVER C; TOMES CN; RODRÍGUEZ EM; MAYORGA LS

PLoS ONE

Public Library of Science (PLoS)

Lugar: San Francisco, CA; Año: 2009 vol. 4 p. 1 - 10

1932-6203

Hydrocephalus with hop gait (hyh) is a recessive inheritable disease that arose spontaneously in a mouse strain. A missense mutation in the Napa gene that results in the substitution of a methionine for isoleucine at position 105 (M105I) of αSNAP has been detected in these animals. αSNAP is a ubiquitous protein that plays a key role in membrane fusion and exocytosis. In this study, we found that male hyh mice with a mild phenotype produced morphologically normal and motile sperm, but had a strongly reduced fertility. When stimulated with progesterone or A23187 (a calcium ionophore), sperm from these animals had a defective acrosome reaction. It has been reported that the M105I mutation affects the expression but not the function of the protein.Consistent with an hypomorphic phenotype, the testes and epididymides of hyh micehad low amounts of the mutated protein. In contrast, sperm had αSNAP levels indistinguishable from those found in wild type cells, suggesting that the mutatedprotein is not fully functional for acrosomal exocytosis. Corroborating this possibility, addition of recombinant wild type αSNAP rescued exocytosis in streptolysin O17permeabilized sperm, while the mutant protein was ineffective. Moreover, addition ofrecombinant αSNAP.M105I inhibited acrosomal exocytosis in permeabilized human and wild type mouse sperm. We conclude that the M105I mutation affects theexpression and also the function of αSNAP, and that a fully functional αSNAP is necessary for acrosomal exocytosis, a key event in fertilization