Occurrence of androgen and estrogen receptor mRNAs in the Harderian gland: A comparative survey

Abstract

In Rana esculenta the presence of an androgen receptor in both the male and female Harderian gland (HG) has been demonstrated. Hybridization analysis has evidenced a high degree of homology between the rat androgen receptor cDNA and the frog androgen receptor mRNA (fARmRNA). Correspondingly the molecular size of fARmRNA is similar to those described in mammals (9.4 kb). In in vivo experiments testosterone (T) increases the levels of fARmRNA. The use of the antiandrogen alone or in combination with T prevents the increase of fARmRNA. In the control animals a loss of fARmRNA has been observed. In primary cultures of HG cells, the steady-state levels of fARmRNA increase in the cells exposed to T. These results suggest that T exerts an autoinduction on its own receptor, increasing the levels of fARmRNA. In Xenopus laevis the HG shows a sexual dimorphism of the protein pattern. The female shows two major proteins (210 and 180 kDa). Administration of estradiol to the male shifts the protein pattern into the female one. In this respect an estrogen receptor mRNA (ERmRNA) has been found in the female gland and can be induced in the male one. No ARmRNA has been detected in either sexes. A similar sex dimorphism has been found in Gallus domesticus. The female pattern is characterised by a protein fraction of about 210 kDa, the male one by a protein fraction of about 180 kDa. In 4-day-old chicks no sex differences have been found. An ERmRNA is expressed in the female, while no ARmRNA has been detected in both sexes. Neither AR nor ER mRNAs have been detected in the chick HG. Among mammals the HG of the hamster (Mesocricetus auratus) shows an androgen-dependent sex dimorphism. In in vitro experiments T 10−12 M induces a onefold increase of ARm-RNA with respect to unexposed cells. This effect reaches its maximum (4.4-fold) when cells are exposed to T 10−8 M. The size of the hamster ARmRNA is similar to that observed in other mammals (9.5 kb). The above results suggest that in the HG the phenomenon of autoinduction occurs and that there is a relationship between the androgen or estrogen dependence of the HG and the digamety of the species. © 1996 Wiley-Liss, Inc.