Independent differentiation of mammotropes and somatotropes in the chicken embryonic pituitary gland

Abstract

It has been reported that mammotropes in a rodent pituitary gland are derived from somatotropes via somatomammotropes (SMTs), cells that produce both growth hormone (GH) and prolactin (Prl). However, no studies have been done on the transdifferentiation of somatotropes in the chicken pituitary gland. In this study, in order to determine the origin of mammotropes, we studied detail property of appearance of chicken somatotropes, mammotropes and pit-1 cells and then evaluated the existence of SMTs in the chicken embryonic pituitary gland. Immunohistochemical analysis revealed that GH-immunopositive (GH-ip) cells appeared on embryonic day (E) 14 and were mainly distributed in the caudal lobe, while Prl-immunopositive (Prl-ip) cells appeared in the cephalic lobe of the pituitary gland on E16. In situ hybridization (ISH) and RT-PCR analysis showed that expression of GH and Prl mRNA starts at E12 in the caudal lobe and at E14 in the cephalic lobe respectively. Pit-1 mRNA was first detected on E5 by RT-PCR, and pit-1 mRNA-expressing cells were found in the cephalic lobe on E8. Then with the ontogeny of the chicken, these cells spread into both lobes. Using a double staining method with ISH and immunohistochemistry, we could not detect the existence of SMTs in the chicken embryonic pituitary gland even in the marginal region of either lobe. These results suggest that chicken somatotropes and mammotropes independently appear in different lobes of pituitary gland and that transdifferentiation from somatotropes to mammotropes is not the central route for differentiation of mammotropes in the embryonic chicken pituitary gland.

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.…”

Hypophyseal corticosteroids stimulate somatotrope differentiation in the embryonic chicken pituitary gland

“…It is well established that the chicken anterior pituitary gland can be divided into two lobes, caudal and cephalic lobes by their morphological structures. We have reported that embryonic somatotropes were diVerentiated in the caudal lobe at E12 and that the cells did not transdiVerentiate to mammotropes (Zheng et al 2006). In this study, we clearly showed that corticosteroid treatment signiWcantly increased the staining intensity and number of GH mRNA-expressing cells in not only the caudal lobe but also the cephalic lobe of the pituitary gland.…”

“…Studies on somatotropes in the embryonic chicken pituitary gland have shown that somatotropes commence diVerentiation between embryonic day (E) 14 and E16 in the caudal lobe (Thommes et al 1987;Porter et al 1995). We have reported that growth hormone (GH) mRNA-expressing cells Wrst appear in the ventral region of the caudal lobe at E12 and are located in the caudal lobe of the chicken pituitary gland until adulthood (Zheng et al 2006). We also found that mammosomatotropes, which are thought to be the intermediate cell type in transdiVerentiation of somatotropes to mammotropes in the rodent (Frawley et al 1985;Frawley and Boockfor 1991), did not appear in the embryonic chicken pituitary gland, suggesting that chicken somatotropes and mammotropes independently diVerentiate in the normal state.…”

The histochemistry and cell biology vade mecum: a review of 2005–2006

“…Zheng et al (2006) have studied the transdiVerentiation of somatotropes in the chicken pituitary gland. For this, they studied the details of appearance of chicken somatotropes, mammotropes and pit-1 cells and then evaluated the existence of SMTs in the chicken embryonic pituitary gland.…”