Developmental changes of Islet-1 and its co-localization with pituitary hormones in the pituitary gland of chick embryo by immunohistochemistry

Although Islet-1 expression in the pituitary gland of early mouse embryo has been previously described, there are no reports concerning the correlation of Islet-1 expression with lineage restrictions in cell types at the later stages of pituitary development. The role of Islet-1 in chickens is also unknown. The purpose of this study was to follow, by using immunohistochemistry, the ontogeny of pituitary Islet-1 and the various cell types that contain Islet-1 throughout chick embryo development. A few Islet-1-immunopositive (Islet-1⁺) cells were first detected in the pituitary primordium in two out of six embryos at embryonic day 5.5 (E5.5), most of the Islet-1⁺ cells being ventrally located. As development progressed, many more Islet-1⁺ cells were observed throughout the pars distalis. The relative percentage of Islet-1⁺ cells amongst the total Rathke’s pouch cells was 4.4% at E6.5. This increased significantly, reaching 11.1% by E10.5, followed by no significant change until hatching. Dual immunohistochemistry showed that adrenocorticotrophs, somatotrophs and lactotrophs did not express Islet-1. The cellular types expressing Islet-1 included luteinizing-hormone-positive (LH⁺) gonadotrophs and thyroid-stimulating-hormone-positive (TSH⁺) thyrotrophs. The cells co-expressing LH and Islet-1 were initially detected at E6.5, the proportion of LH⁺ cells possessing Islet-1 being about 4%; this increased to 63% at E14.5, followed by no significant changes until hatching. TSH and Islet-1 co-localized cells were first observed at E10.5, with about 37% TSH⁺ cell expressing Islet-1; this increased to about 50% by E16.5, after which there was no evident change until hatching. These results suggest that Islet-1 is involved in determining the cell lineages, proliferation, differentiation and maintenance of hormone-secreting functions of pituitary gonadotrophs and thyrotrophs of chick embryo. J. Liu and Y. He contributed equally to this article. This work was supported by grants from Beijing Natural Science Foundation (6042013) and the Natural Science Foundation of China (30471264, 30325034).