Sex-determining region Y (Sry) triggers testis development in mammals, and the presence or absence of testicular secretion determines their sex-specific brain phenotype. Mice with Y chromosome replaced by that of Mus domesticus poschiavinus (Y^POS) frequently display sex reversal due to delayed Sry expression. However, brain sexual dimorphism under conditions of disorders of sex development remains unclear. Here, we report sex differences in the sexually dimorphic nucleus of the preoptic area, delineated by cells positive for calbindin D28k, a male-predominant neuronal marker (CALB-SDN), in Y^POS mice. The mice were divided into females and males according to gonadal phenotype. Cells immunoreactive (ir) for calbindin D28k (CALB) were more extensively distributed in male Y^POS mice, compared with females. The CALB-ir cell numbers in the CALB-SDN were significantly higher in Y^POS males than in Y^POS females, which had numbers comparable to wild type females. No left-right differences in CALB-ir cell numbers were observed in the CALB-SDN. Collectively, these results demonstrate that sexual dimorphism of the CALB-ir cell cluster in the CALB-SDN strongly correlates with the gonadal sex phenotype rather than with the chromosomal sex in the Y^POS mice, suggesting the effect of testicular secretion on the brain sexual differentiation with aberrant Y-linked gene expression.

Prostate cancer is one of the most common malignancies in men and remodeling of extracellular collagen, especially collagen type I immensely contributes to the progress of prostate cancer. Discoidin domain receptor 2 (DDR2) is a receptor of collagen type I and transmits intracellular signaling in not only normal cells but also malignant cells, facilitating tumor progression. However, clinical and biological significance of DDR2 has not been well examined in prostate cancer. We therefore immunolocalized DDR2 and collagen type I in 117 prostate carcinoma tissues and correlated their immunoreactivity with clinicopathological characteristics of prostate cancer. We also conducted in vitro experiments using human prostate cancer cell lines to confirm the findings from immunohistochemical study. DDR2 immunoreactivity was positively associated with an aggressive phenotype of prostate cancer, partially in association with dense collagen I tissues which consisted of thin fibers. In addition, DDR2 immunoreactivity was significantly correlated with adverse clinical outcomes of prostate cancer. In vitro experiments revealed that DDR2 promoted proliferation and migration of PC-3 and DU-145 prostate cancer cell lines. It is therefore speculated that DDR2 promoted prostate cancer progression by interacting with collagen I, serving as a potent prognostic factor in prostate cancer.