Although mastermind-like domain containing 1 (MAMLD1) (CXORF6) on human chromosome Xq28 has been shown to be a causative gene for
46,XY disorders of sex development with
hypospadias, the
biological function of MAMLD1/Mamld1 remains to be elucidated. In this study, we first showed gradual and steady increase of testicular Mamld1
mRNA expression levels in wild-type male mice from 12.5 to 18.5 d postcoitum. We then generated Mamld1 knockout (KO) male mice and revealed mildly but significantly reduced testicular
mRNA levels (65-80%) of genes exclusively expressed in Leydig cells (Star,
Cyp11a1, Cyp17a1, Hsd3b1, and Insl3) as well as grossly normal testicular
mRNA levels of genes expressed in other cell types or in Leydig and other cell types. However, no demonstrable abnormality was identified for
cytochrome P450 17A1 and 3β-hydroxysteroid
dehydrogenase (HSD3B)
protein expression levels, appearance of external and internal genitalia, anogenital distance, testis weight, Leydig cell number, intratesticular
testosterone and other
steroid metabolite concentrations, histological findings, in situ hybridization findings for sonic hedgehog (the key molecule for genital tubercle development), and immunohistochemical findings for anti-Müllerian
hormone (Sertoli cell marker), HSD3B (Leydig cell marker), and DEAD (
Asp-Glu-
Ala-Asp) box
polypeptide 4 (germ cell marker) in the KO male mice. Fertility was also normal. These findings imply that Mamld1 deficiency significantly reduces
mRNA expression levels of multiple genes expressed in mouse fetal Leydig cells but permits normal genital and reproductive development. The contrastive phenotypic findings between Mamld1 KO male mice and MAMLD1 mutation positive patients would primarily be ascribed to species difference in the fetal sex development.