In mammals, spermatozoa spread from the site of insemination toward the site of fertilization in a controlled way that allows the encounter of male and female gametes in a viable and competent state, and in ratios adequate to assure fertilization with minimum risk of polyspermy.
Little is known about the regulation of the patency of the UTJ, nor about the means by which sperm enter the oviduct.
Our study was undertaken to determine why sperm from calmegin-knockout mice cannot enter the oviduct and thus to learn more about how sperm normally enter the oviduct.
Transillumination of freshly dissected oviducts 1–2 h after coitus in early estrus revealed that the initial intramural region of the UTJ had constricted, while the extramural UTJ, closer to the ovary, was patent and contained many motile sperm .
Most of those sperm were stuck by their heads to the mucosal epithelium, a phenomenon believed to be responsible for forming a sperm reservoir prior to ovulation, but which might also enable sperm to gain a foothold in the UTJ.
Chimeric ejaculates contained wild-type, nonfluorescent sperm as well as sperm with EGFP-tagged acrosomes and the defective calmegin gene.
Transgenic, wild-type, and chimeric males were mated to wild-type females; however, only wild-type sperm were ever found within the oviducts.
At least 200 sperm were analyzed per sample to evaluate the percentage of motile sperm, straight line velocity, curvilinear velocity, amplitude of lateral head displacement, and linearity. Fertilized eggs were incubated in KSOM medium until the 8-cell-morula stage, and were evaluated for X-chromosome-associated EGFP fluorescence, using a fluorescein epifluorescence filter set (U-MNIBA: BP470-490 BA515-550 DM505; Olympus, Tokyo, Japan) in an inverted microscope.
The following settings were used: temperature, 37°C; 10× negative phase-contrast optics; frames acquired, 30; frame rate, 60 Hz; minimum contrast, 60; minimum cell size, 3 pixels; minimum static contrast, 30; low average path velocity cutoff, 5.0 μm/sec; static head size, 0.32 to 2.99; static head intensity, 0.42 to 1.60; and magnification, 1.95. Embryos with no fluorescence were considered to be wild-type males and were used to produce aggregation chimeras.
Substantial numbers of sperm are found in histologic sections of the oviductal isthmus within 30 min of mating.
The ostium of the colliculus tubarius, the uterine portal to the UTJ, closes within an hour of coitus in early estrus in the mouse .
Loss of calmegin, a testis-specific putative chaperone protein of the endoplasmic reticulum, leads to male sterility because the sperm show defects in migration into the oviduct and do not bind to the zona pellucida.