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Light Microscopic Appearance of the Testis of FORKO Mice At 3 and 6 mo of age, the seminiferous tubules in the testis of FORKO mice showed smaller profile areas compared with wild-type mice (Fig. 1, a and b). In addition, while the testis of wild-type mice displayed a homogenous, compact seminiferous epithelium, where germ and Sertoli cells were closely associated with each other (Fig. 1, a and c), the FORKO mice presented a varying and vacuolated appearance (Figs. 1, b and d, and 2, a and b). Although some tubules at both ages seemed normal in cross-sectional profile (approximately 40%), nearly one half of the circumference of seminiferous epithelium of other tubules in the FORKO mice appeared disrupted, showing large dilated spaces between the epithelial cells (Figs. 1, b and d, and 2, a and b). This semilunar disruption pattern did not appear to be associated with a specific stage of the cycle of the seminiferous epithelium (Figs. 1, b and d, and 2, a and b). In areas where the FORKO tubules were abnormal, large dilated spaces often extended from the base of the epithelium toward the lumen, and at the base, these spaces at times hovered over the nuclei of Sertoli cells (Fig. 2, a and b). FIG. 1. Light micrographs of seminiferous tubules of the testis of wild-type (a, c) and FORKO (b, d) mice at 3 mo of age. Note reduction in size of the tubules of FORKO mice (b) as compared with their wild-type counterparts (a). In a and c, the seminiferous epithelium (SE) shows a close association of Sertoli cells with germ cells. The heads of the elongating spermatids (arrows) are tightly apposed to the enveloping Sertoli cells in wild-type mice (a, c). In contrast, in b and d, large empty spaces appear in the epithelium (stars), which tend on the whole to be localized to half the circumference of the affected tubules. Note that the dilated spaces (stars) in the midregion of the epithelium surround the heads of elongating spermatids (arrows). Gc, Germ cells; N, nucleus of Sertoli cell; IS, interstitial space; L, lumen. a, b) Original magnification X250; (c) original magnification X390; (d) original magnification X1000. FIG. 2. Low (a) and high (b) power light micrographs of seminiferous tubules of FORKO mice at 6 mo of age. In a and b, the highly dilated translucent spaces (stars) are situated basally in the epithelium, with some enveloping the heads of elongating spermatids (thin arrows). In a and b, some spaces (thick arrows) are confluent with areas containing the Sertoli nucleus (N). The extensive nature of the dilated spaces gives rise to anastomotic cords (arrowheads) of spherical germ cells (Gc), which themselves do not appear to be dilated. Despite the extensive epithelial dilatations, there is no suggestion of pyknosis in the nuclei of Sertoli cells or of apoptotic cells. In the dilated spaces, numerous membranous profiles of varying sizes and shapes (curved arrows) are evident, as well as small particulate and granular material (square). a) Original magnification X390; (b) original magnification X1000. FIG. 3. Light micrographs of seminiferous tubules of 3-mo-old wild-type (a) and FORKO (b) mice immunostained with anti-prosaposin antibody. Note reduction in the profile area of the tubules between wild-type and FORKO mice. Sertoli cells (arrows) are highly reactive and extend from the base of the seminiferous epithelium (SE) to the lumen (L) in both a and b; germ cells are unreactive. a, b) Original magnification X390.