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Abstract

Volume 12, Issue 6 (November 2010) 12, 853–861; 10.1038/aja.2010.52

Protein tyrosine phosphorylation of the human sperm head during capacitation: immunolocalization and relationship with acquisition of sperm-fertilizing ability

Arcangelo Barbonetti1,2, Maria Rosaria C. Vassallo1, Giuliana Cordeschi1, Dimitrios Venetis1, Andrea Carboni1, Alessandra Sperandio1, Giorgio Felzani2, Sandro Francavilla

1 Andrology Unit, Department of Internal Medicine, University of L'Aquila, Coppito 67100, L'Aquila, Italy
2 Istituto di Ricovero e Cura a Carattere Scientifico, S.Raffaele, Sulmona 67039, Italy

Correspondence: Prof. Felice Francavilla,francavi@cc.univaq.it

Received 18 February 2010; Revised 13 May 2010; Accepted 7 June 2010; Published online 9 August 2010.

Abstract

The occurrence of tyrosine phosphorylation (TP) in the sperm head during capacitation has been poorly investigated, and no data exist on the relationship of its dynamics with the acquisition of sperm fertilizing ability. This study localized TP of head proteins in human spermatozoa during capacitation and explored its relationship with acquisition of the ability to display progesterone (P)-stimulated acrosome reactions (ARs) and to penetrate zona-free hamster oocytes. By immunofluorescence, TP immunoreactivity was revealed in the acrosomal region of formaldehyde-fixed/unpermeabilized samples, whereas it was abolished in fixed/permeabilized samples, in which TP immunoreactivity was high in the principal piece. No TP immunoreactivity was detectable in unfixed spermatozoa. Head TP immunoreactivity was localized externally to the acrosome, close to the cytoplasmic membrane, as assessed by transmission electron microscopy. The increase in head TP was an early event during capacitation, occurring within 1 h in capacitating conditions. At this time, the P-stimulated ARs were also increased, whereas egg penetration was as poor as in uncapacitated spermatozoa. At 5 h of capacitation, the extent of neither head TP nor the P-induced ARs were greater than that at 1 h, whereas egg penetration had significantly increased. Seminal plasma inhibited head TP, P-induced ARs and egg penetration. None of these inhibitory effects, unlike those on tail TP, were prevented by the cAMP analogue dbcAMP (N,2-O-dibutyryladenosine 3′,5′-cyclic monophosphate). In conclusion, head TP is a subsurface event occurring early during capacitation and is closely related to acquisition of the ability to display P-stimulated ARs, whereas the ability to fuse with oolemma and to decondense is a later capacitation-related event.

Keywords: acrosome reaction; capacitation; human spermatozoa; sperm–oocyte fusion; tyrosine phosphorylation

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