Proteins of the acrosomal region in mouse sperm: immunological probes reveal post-testicular modifications.

Due to the central role the acrosomal region plays in sperm-egg interactions, monoclonal antibodies (mAbs) were used to identify components of this domain in mouse sperm. Several sperm proteins that localize specifically to the anterior acrosomal region are described here in terms of electrophoretic mobility, susceptibility to proteolytic degradation, and post-translational modification during epididymal transit. Six different mAbs were used, each recognizing a distinctive antigen (Ag) or set of Ags in cauda epididymal mouse sperm: a doublet of 185/200 Kd (M42 mAb); 150-160 Kd (M5 mAb); 105 Kd (W71 mAb); 21, 35, and 60 Kd (M41 mAb); 27 and 33 Kd (W33 mAb); and 57 and 86 Kd (W108 mAb). Previously reported work implicates two of these, M42 Ag and M5 Ag, as participants in sperm-zona interaction (Saling and Lakoski: Biol Reprod 33:527-536, 1985; Saling: Dev Biol 117:511-519, 1986; and Lakoski et al.: Biol Reprod 38:221-233, 1988). Recognition of some (M42, M5, W108), but not all (W33), of the Ags by their corresponding mAbs was affected by sperm incubation with proteases (trypsin or collagenase). Evidence of post-translational modification during epididymal maturation was suggested by altered electrophoretic mobility of several of the Ags (M42, M5, W33, and W108) accompanying sperm transit from proximal to distal epididymis. Retention of sperm within the caput epididymis prevented structural alterations for the four proteins examined, indicating that spatial rather than temporal factors are critical for Ag modification in maturing mouse sperm.