Yoshiakira Kanai

The cerebellar, ocular, craniofacial, and genital (COFG) syndrome is a human genetic disease that is caused by MAB21L1 mutations. A COFG mouse model with Mab21l1 ‐null mutation causes severe microphthalmia and fontanelle dysosteogenesis, similar to the symptoms in human patients. One of the typical symptoms is scrotal agenesis in male infants, while male Mab21l1 ‐null mice show hypoplastic preputial glands, a rodent‐specific derivative of the cranial scrotal fold. However, it is still unclear where and how MAB21Ll acts in the external genitalia in both mice and humans. Here we show that, at the neonatal stage, MAB21L1 expression in the external genitalia was restricted to two mesenchymal cell populations—underneath the scrotal and labial skin and around the preputial and clitoral glands (PG/CG). Morphometric analyses of the Mab21l1 −/− pups revealed a significant reduction in the external size of the scrotum, vulva, and CG, as well as PG. In the periglandular region around PG and CG, the periglandular mesenchymal cells showed a drastic reduction in both cell density and immunoreactive signals for several extracellular matrix proteins (e.g., collagen I, fibronectin, and proteoglycans), together with their reduced Ki67‐positive cell proliferation index. In the Mab21l1 −/− PG/CG, together with reduced vascularization, the glandular epithelia displayed atrophy with discontinuous basal lamina along the basal surface and defective glycogen accumulation in their cytoplasm. Under a 5‐day organ culture of the isolated PG, the Mab21l1 −/− explants showed poor outgrowth and retention of the glandular structure in vitro. However, the addition of exogenous Matrigel could partially rescue such tissue‐autonomous phenotypes, showing glandular morphology similar to that of the wild‐type explants. These findings suggest that MAB21L1+ mesenchymal cells play a crucial role in providing nutrient ECM support for glandular outgrowth and morphogenesis in the peripheral external genitalia.