Novel cellular evidence of oviduct secretions in the Chinese soft-shelled turtle Pelodiscus sinensis

The oviduct is the location of fertilization and sperm storage. We examined the ultrastructure of the oviduct epithelium and its glandular secretions in the isthmus, uterus and vagina of Chinese soft-shelled turtle Pelodiscus sinensis using light and transmission electron microscopy. The epithelium in these segments is lined with ciliated, secretory and other cells; the first two cell types span the entire epithelium, with secretory cells being predominant. The ciliated cells are characterized by the presence of a secretory vacuole that releases apocrine secretions into the lumen, whereas the secretory cells contain typical biphasic granules with both dark and light aspects. The third type of cells observed have wider proximal portion, abundant mitochondria, vacuoles, and narrow nuclei. The storage of spermatozoa is restricted to the isthmus, uterus, and vagina. In addition, the gland cells show prominent features, including the presence of granules of different shapes, sizes, and electron densities. The synthesis of these granules is described for the first time in this study. Mitochondria appear to play an important role in the formation of dense granules, the rough endoplasmic reticulum and microfilaments may also play a role in the maturation of these dense granules. After completing the maturation process, these granules are released into the lumen of the gland cells.