A new sex dimorphism in the Harderian gland of the frog Rana esculenta.

The Harderian gland (hg) is the only gland found in the orbits of the frog Rana esculenta, and it has the primary role of lubricaing the eyes. The secretory activity of the frog hg is seasonal, showing the highest value in summer. To date, there is little information on frog hg gene expression, previously we identified a novel mRNA named "harderin" whose deduced protein has no significant homology with other proteins. This transcript was detected only in the RNA of frog hg suggesting a tissue specific expression of the protein. The present study reports, for the first time, that harderin transcript is differentially expressed in the hg of both sexes of R.esculenta during the whole annual secretory cycle, suggesting a sexual dimorphism. RT-PCR analysis, performed throughout the annual secretory cycle, revealed that harderin transcript is expressed during the whole year in the hg of both sexes, showing a higher level of expression in the female glands at anytime. In particular, two peaks of expression, in February and in June, were observed in the female glands, while only the February peak was observed in those of males. In situ hybridization indicated thar harderin mRNA was expressed in the cytoplasm of the majority of acinar secretory cells and confirmed that female glands had significantly higher levels of expression than those of males. Experiments of castration and/or replacement therapy performed inn June, when estradiol peaks only in females, evidenced a significant decrease of harderin expression in the hg of females; this effect is counteracted by estradiol (testosterone dministration had no effect), suggesting that this new sexual dimorphism is under estradiol control.