Molecular mechanisms involved in gamete interaction: evidence for the participation of cysteine-rich secretory proteins (CRISP) in sperm-egg fusion.
Epididymal protein DE and testicular protein Tpx-1 are two cysteine-rich secretory proteins also known as CRISP-1 and CRISP-2, respectively. DE/ CRISP-1 is localised on the equatorial segment of acrosome-reacted sperm and participates in rat gamete fusion through its binding to egg-complementary sites. Recent results using bacterially-expressed recombinant fragments of DE as well as synthetic peptides revealed that the ability of DE to bind to the egg surface and inhibit gamete fusion resides in a region of 12 amino acids corresponding to an evolutionary conserved motif of the CRISP family (Signature 2). Given the high degree of homology between DE/CRISP-1 and Tpx-1/CRISP-2, we also explored the potential participation of the testicular intra-acrosomal protein in gamete fusion. Results showing the ability of recombinant Tpx-1 to bind to the surface of rat eggs (evaluated by indirect immunofluorescence) and to significantly inhibit zona-free egg penetration, support the participation of this protein in gamete fusion through its interaction with egg-binding sites. Interestingly, rat Tpx-1 exhibits only two substitutions in Signature 2 when compared to this region in DE. Together, these results provide evidence for the involvement of both epididymal DE/CRISP-1 and testicular Tpx-1/CRISP-2 in gamete fusion suggesting the existence of a functional cooperation between homologue molecules as a mechanism to ensure the success of fertilisation.
Da Ros
V
V
Instituto de Biología y Medicina Experimental (IBYME-CONICET), Vuelta de Obligado 2490, (1428) Buenos Aires, Argentina.
Busso
D
D
Cohen
D J
DJ
Maldera
J
J
Goldweic
N
N
Cuasnicu
P S
PS
D020101:Acrosome Reaction / Q000502:physiology; D000818:Animals; D015815:Cell Adhesion Molecules; D005260:Female; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D010063:Ovum / Q000378:metabolism; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013094:Spermatozoa / Q000378:metabolism
C103538:CRISP1 protein, human; C062621:CRISP2 protein, human; D015815:Cell Adhesion Molecules; D006023:Glycoproteins; D008562:Membrane Glycoproteins