Preferential expression of osteocalcin-related protein mRNA in gonadal tissues of male mice

It was recently reported that the mouse genome contains an osteocalcin cluster formed by three genes, OG1, OG2 and ORG, in order from the 5' to the 3' end of the cluster. These three genes exhibit close structural homology. OG1 and OG2 are abundant in bone, but ORG is expressed in nonosteoid tissues, especially in kidney and lung. Previous studies using transgenic mice carrying diphtheria toxin A-chain gene linked to the rat osteocalcin (OG2) promoter have revealed that the OG2 promoter is active not only in osteoblasts, but also in testis. In this study, reverse transcription-polymerase chain reaction was used to study the expression of these three genes in mouse tissues (including testis). Here we report for the first time that mouse ORG is extensively transcribed in male gonadal tissues including seminal vesicle, preputial gland, testis, caput epididymis and cauda epididymis. These findings suggest that ORG may play a role in differentiation and/or maintenance of male gonadal tissues.