Germ cell loss is associated with fading Lin28a expression in a mouse model for Klinefelter's syndrome

Klinefelter's syndrome is a male sex-chromosomal disorder (47,XXY), causing hypogonadism, cognitive and metabolic deficits. The majority of patients are infertile due to complete germ cell loss after puberty. As the depletion occurs during development, the possibilities to study the underlying causes in humans are limited. In this study, we used the 41,XX(Y*) mouse model to characterise the germ line postnatally. We examined marker expression of testicular cells focusing on the spermatogonial stem cells (SSCs) and found that the number of germ cells was approximately reduced fivefold at day 1pp in the 41,XX(Y*) mice, indicating the loss to start prenatally. Concurrently, immunohistochemical SSC markers LIN28A and PGP9.5 also showed decreased expression on day 1pp in the 41,XX(Y*) mice (48.5 and 38.9% of all germ cells were positive), which dropped to 7.8 and 7.3% on 3dpp, and were no longer detectable on days 5 and 10pp respectively. The differences in PCNA-positive proliferating cells in XY* and XX(Y*) mice dramatically increased towards day 10pp. The mRNA expression of the germ cell markers Lin28a (Lin28), Pou5f1 (Oct4), Utf1, Ddx4 (Vasa), Dazl, and Fapb1 (Sycp3) was reduced and the Lin28a regulating miRNAs were deregulated in the 41,XX(Y*) mice. We suggest a model for the course of germ cell loss starting during the intrauterine period. Neonatally, SSC marker expression by the already lowered number of spermatogonia is reduced and continues fading during the first postnatal week, indicating the surviving cells of the SSC population to be disturbed in their stem cell characteristics. Subsequently, the entire germ line is then generally lost when entering meiosis.