Why do penetrating sperm create an oblique path in the zona pellucida?

Acrosin antibodies and infertility. I. Detection of antibodies towards proacrosin/acrosin in women consulting for infertility and evaluation of their effects upon the sperm protease activities

“…Evidence has accumulated supporting the participation of the proacrosin/ acrosin system in eutherian fertilization: the enzymatic activity of acrosin is involved in the dissolution of the acrosomal matrix and the regulated release of the acrosomal contents during the acrosomal reaction (41). In addition, it was previously suggested that proacrosin/acrosin would participate in sperm-zona pellucida (ZP) binding by interaction with ZP glycoproteins (36,(42)(43)(44)(45), and the mature enzyme would help sperm penetration by limited and specific proteolysis of ZP glycoproteins (34), although the latter role is currently under revision (46). Specific antibodies to human proacrosin/acrosin have been developed in animal models (44,47,48), demonstrating the ability of this protein system to trigger an immune response.…”

Influence of sperm impact angle on successful fertilization through mZP oscillatory spherical net model

“…Bedford [14] speculates that sperm impact angle of π/2 will probably provide holes in the ZP during its stretching during growth of the embryo. Angle 2π/3, according to the form of generalized Lissajous curves, provides asynchronous dynamical state of the knot molecules (see Figs.…”

“…This process should have particular timing as ZP dynamically changes its mechanical properties during the processes of oogenesis, fertilization, and preimplantation development [6][7][8][9][10][11][12]. Ultrastructural analysis of mammal ZP by using transmission electronic microscopy (TEM) showed that the spermatozoid penetrated ZP by an oblique path [13,14], but the specific angle is still not known. "Binding of the sperm head by its flat surface could initiate the oblique angle of its subsequent penetration through the eutherian zona.…”

“…"Binding of the sperm head by its flat surface could initiate the oblique angle of its subsequent penetration through the eutherian zona. The tangential trajectory of that path ensures that it then closes as the zona stretches and thins during expansion of the blastocyst, so preventing the development of a hole(s)" [14]. Neither in vivo nor in vitro conditions of fertilization are always successful.…”

Mysteries and unsolved problems of mammalian fertilization and related topics

“…Spermatozoa of many species (e.g., hamster, rabbit, guinea pig, pig, sheep) pass through the zona pellucida obliquely (e.g., see Dickmann and Dziuk [ 175 ]). Bedford [ 176 ] tried to explain why it must be that way. However, rat and human spermatozoa can penetrate the zona perpendicularly [ 69 , 177 ].…”