Development of gonadotropes in the chicken embryonic pituitary gland

Although a number of immunohistochemical studies have been carried out on the differentiation of chicken gonadotropes during embryogenesis, the temporal and spatial properties of appearance of gonadotropes are not clear. In this study, we studied the appearance and morphological characteristics of gonadotropes in the embryonic and adult chicken anterior pituitary glands using RT-PCR, in situ hybridization and immunohistochemistry. For this purpose, we raised specific antisera against chicken follicle-stimulating hormone beta-subunit (cFSHbeta) and chicken luteinizing hormone beta-subunit (cLHbeta) based on each putative amino acid sequence. RT-PCR analysis revealed that cFSHbeta mRNA was expressed from embryonic day 7 (E7). Chicken FSHbeta mRNA-expressing (-ex) and -immunopositive (-ip) cells started to appear in the ventral part of the caudal lobe in the anterior pituitary gland at E8. Chicken LHbeta-ip cells were also first observed there at E8, but cLH mRNA expression was confirmed from E4 by RT-PCR analysis. The distribution of these chicken gonadotropin-ex and -ip cells spread from the ventral part to dorsal part in the caudal lobe around E10 and subsequently expanded to the cephalic lobe from E12 to E20. These cells were morphologically classified into two types (round- and club-shaped cells). It was found that the density of gonadotropin-ip cells in the caudal lobe was always higher than that in the cephalic lobe throughout the period of development. To the best of our knowledge, this is the first report focusing on the differentiation of chicken gonadotropes by assessment of both protein and mRNA of chicken gonadotropin.