Evidence that lactotrophs do not differentiate directly from somatotrophs during chick embryonic development

Abstract

It is generally accepted that, in mammals, lactotrophs differentiate from somatotrophs through an intermediate cell type, the mammosomatotroph. However, little information exists about mammosomatotrophs and their relationship with lactotroph development in non-mammalian vertebrates. We reported previously that corticosterone (CORT) can induce both somatotroph and lactotroph differentiation in cultures of chicken embryonic pituitary cells. Our current objectives were to determine the abundance of mammosomatotrophs during chicken pituitary development, to identify mammosomatotrophs during CORT induction of lactotrophs, and to explore whether lactotrophs induced by CORT are derived from somatotrophs. Cells that produced prolactin (PRL) only, growth hormone (GH) only or both hormones simultaneously were detected by three approaches -dual immunofluorescence, a combination of immunofluorescence and immunocytochemistry (ICC), and by ICC using combinations of antibodies to GH and PRL. Mammosomatotrophs were not detected between embryonic day (E) 16 and E20, even though lactotrophs increased from nearly absent to greater than 10% of all pituitary cells during this period. CORT induced more than 10% of all E13 pituitary cells to produce PRL, while the percentage of mammosomatotrophs remained at less than 1% of all cells. When cells from the cephalic and caudal lobes of the anterior pituitary were treated separately, CORT increased GH cells in cultures from the caudal lobe. No PRL cells were found in the caudal lobe. In the cephalic lobe, CORT increased lactotrophs, while GH cells were barely detected. In summary, mammosomatotrophs are rare during chicken pituitary development, and CORT does not induce lactotrophs from somatotrophs. These findings indicate that, unlike in mammals, lactotrophs do not differentiate from somatotrophs during chicken embryonic development.

Somatotrophs and lactotrophs: an immunohistochemical study of Gallus domesticus pituitary gland at different stages of induced moult

“…For instance, in rats the appearance of ir-PRL occurs around birth and approximately one week after GH cell differentiation. 18 In our study there was an increase in immunoreactive cell numbers at the start of moulting, which decreased further with the passage of time. In our opinion, the decrease in ir-PRL cell numbers in the process of induced moult may be due to the effects of decreasing light in the moulting period.…”

Expression patterns of hormones, signaling molecules, and transcription factors during adenohypophysis development in the chick embryo

“…In the chick, Gh and Prl mRNA are observed in distinct subdomains of the embryonic pituitary gland from the onset of their expression. Based on the distinct localization of GH and PRL in the caudal and cephalic lobes, respectively, our data clearly support previous studies that suggest that these two cell types are unlikely to originate from a common somatolactotrope progenitor capable of producing both hormones (Fu et al, 2004;Zheng et al, 2006). However, these data do not preclude the possibility that somatotropes and lactotropes arise from a common ''pre-hormone'' progenitor that becomes distributed throughout both lobes of the pituitary gland prior to hormone expression.…”

Use of a prolactin-Cre/ROSA-YFP transgenic mouse provides no evidence for lactotroph transdifferentiation after weaning, or increase in lactotroph/somatotroph proportion in lactation

“…The latter finding was supported more recently by a GH promoter-driven Cre recombinase transgenic mouse model in which 90% of PRL cells appeared to develop entirely independently of the GH lineage (Luque et al . 2007) (as it does in some non-mammalian species (Fu et al . 2004)), and by the observation, also in mice, that estrogen can induce PRL cells to appear prior to the onset of GH gene expression on day 15 of fetal life (Matsubara et al .…”