Rat caltrin protein modulates the acrosomal exocytosis during sperm capacitation.
Caltrin is a small and basic protein of the seminal vesicle secretion that inhibits sperm calcium uptake. The influence of rat caltrin on sperm physiological processes related to fertilizing competence was studied by examining its effect on 1) spontaneous acrosomal exocytosis, 2) protein tyrosine phosphorylation, and 3) sperm-egg interaction. Results show that the presence of caltrin during in vitro capacitation both reduced the rate of spontaneous acrosomal exocytosis without altering the pattern of protein tyrosine phosphorylation, and enhanced the sperm ability to bind to the zona pellucida (ZP). The significantly higher proportion of sperm with intact acrosome observed in the presence of caltrin was accompanied by a strong inhibition in the acrosomal hyaluronidase release. Enhancement of sperm-ZP binding was evident by the increase in the percentage of eggs with bound spermatozoa as well as in the number of bound sperm per egg. Similar results were obtained when the assays were performed using spermatozoa preincubated with caltrin and then washed to remove the unbound protein, indicating that the sperm-bound caltrin was the one involved in both acrosomal exocytosis inhibition and sperm-ZP binding enhancement. Caltrin bound to the sperm head was partially released during the acrosomal exocytosis induced by Ca-ionophore A23187. Indirect immunofluorescence and immunoelectron microscopy studies revealed that caltrin molecules distributed on the dorsal sperm surface disappeared after ionophore exposure, whereas those on the ventral region remained in this localization after the treatment. The present data suggest that rat caltrin molecules bound to the sperm head during ejaculation prevent the occurrence of the spontaneous acrosomal exocytosis along the female reproductive tract. Consequently, more competent spermatozoa with intact and functional acrosome would be available in the oviduct to participate in fertilization.
Cátedra de Bioquímica y Biología Molecular, Facultad de Ciencias Médicas, Universidad Nacional de Córdoba, Córdoba, Argentina.
Andrea
A
Dematteis
Sabrina D
SD
Miranda
Maria L
ML
Novella
Cristina
C
Maldonado
Ruben H
RH
Ponce
Julieta A
JA
Maldera
Patricia S
PS
Cuasnicu
Carlos E
CE
Coronel
D000177:Acrosome / Q000187:drug effects / Q000378:metabolism*; D020101:Acrosome Reaction / Q000187:drug effects; D000818:Animals; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005260:Female; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D029607:Seminal Vesicle Secretory Proteins / Q000494:pharmacology / Q000502:physiology*; D013075:Sperm Capacitation / Q000187:drug effects / Q000502:physiology*; D013084:Sperm-Ovum Interactions / Q000187:drug effects; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism; D015044:Zona Pellucida / Q000378:metabolism
D029607:Seminal Vesicle Secretory Proteins; D011505:Protein-Tyrosine Kinases