Morphogenesis and histochemistry of the developing mouse kidney

A morphological and histochemical investigation was conducted on the pronephros and mesonephros of the mouse embryo from 8.5 through 16.5 days. The pronephros appeared between days 8.5 and 9.5 as a thickening of the somatic layer of the intermediate cell mass. It consisted of three small clusters of cells on either side of the midline dorsally between the somite and the coelom, at the level of somites 8 and 9. The mesonephros arose during day 9 and persisted until day 16. In the male the anterior three tubules were incorporated into the testis at 15.5–16.5 days. The mesonephros consisted of approximately 11 tubules located between somites 10–17. The tubules possessed lumina and connected with the Wolffian duct. Indications of internal and external glomeruli were noted on day 11. The Wolffian duct reached the cloaca at ten days. Strong alkaline phosphatase activity was noted in the differentiating tubules. Cytoplasmic and luminal enzyme activity was observed between 9.3 and 12.5 days indicating possible function at this time. Acid phosphatase was demonstrable in the tubules and duct only on day 11. Ribonucleic acid was observed in the nuclei and cytoplasm of the mesodermal cells as they differentiated into tubules and duct. A decrease in RNA was noted after differentiation was complete. Periodic acid-Schiff material (diastase-stable) was localized in the basement membrane of the tubule and duct cells. A faint positive reaction was also found at the luminal border of the tubules. The strongest reaction was noted in the luminal border at 11.5–12.5 days. Those tubules being incorporated into the genital system in the male were also PAS positive. Morphological and histochemical evidence suggested that the mouse mesonephros, though quasi vestigial, may function for a short time.