The embryological development and cytodifferentiation of the anterior pituitary in the marsupial, Isoodon macrourus

Abstract

Light and electron microscopy were used to study the development of the anterior pituitary gland from fetal stages to the end of pouch life in the marsupial I. macrourus. The early morphological development of the anterior pituitary in I. macrourus follows a similar pattern of events to that described for eutherians. Rathke's and Seessel's pouches were present in 10 1/2 day old embryos. At birth these pouches had formed a multi-chambered vesicle which was still connected to the stomodeum by a thin cord of tissue. A small number of granules (200-400 nm dia.) were found in cells at birth. These cells could not be classified on ultrastructural features but alcian blue-periodic acid Schiffs-orange G staining suggested one cell type was possibly a presumptive thyrotroph. There were no capillaries in the pars distalis at birth. The cords connecting Rathke's and Seessel's pouches to the stomodeum were located at the site of the periosteal bud of the developing basisphenoid which commenced to ossify at 7 days. At this stage presumptive thyrotrophs, gonadotrophs, and somatotrophs could be distinguished using alcian blue-periodic acid Schiffs-orange G staining. However, five cell types could be categorised at the same age using ultrastructural characteristics alone. Precise names for these cells are unavailable but two closely resemble presumptive mammotrophs and thyrotrophs described for another marsupial M. eugenii. By 13 days after birth the anterior pituitary of I. macrourus had become vascular and acidophils were concentrated in a posterior zone. There was little gross morphological change from 13 to 66 days after birth by which the time weaning has occurred. Cilia were seen in cells of the anterior pituitary and mitosis of granulated cells was observed from birth onwards. There is a considerable range of variation in pituitary cytogenesis amongst marsupials, and its functional significance awaits further investigation.

Thyroid hormones during development of a marsupial, the tammar wallaby, Macropus eugenii

“…We do not know what initiates the surge of T4, but it may be that it is preceded by a surge of plasma thyrotrophin (TSH) that is responsible for activating secretion from the thyroid gland. Such a surge in TSH has been reported in the fetal rat (Morreale de Escobar et al 1987) and is consistent with the early appearance of thyrotrophs in the anterior pituitary of the bandicoot (Hall & Hughes, 1985).…”

“…Thyrotrophs are the first cell types to appear in the anterior pituitary of the bandi¬ coot and are present in pouch young on day 7 (Hall & Hughes, 1985). Although a presumptive thyroid gland is present in newborn bandicoots, the first signs of active hormone secretion are not seen until day 30, and a peak in secretory activity is present around day 50 (Johnston & Gemmell, 1987).…”

Origin of Adenohypophysial Lobes and Cells from Rathke’s Pouch in Swiss Albino Mice. Proliferation and Expression of Pitx 2 and Calbindin D28K in Corticotropic and Somatotropic cell Differentiation

“…The development of RP in mice occurs halfway through ontogenesis, as described for other vertebrate groups such as fish and amphibians (Zuber‐Vogeli and Bihoues‐Louis, 1971; Schreibman et al., 1973; Grandi and Chicca, 2004), reptiles (Pearson et al., 1983), birds (Wignstrand, 1951) and in other mammals (Hall and Hughes, 1985). For this reason, it was during ontogeny that we studied the three proliferative regions from which the adenohypophysial lobes originate.…”

Origin of Adenohypophysial Lobes and Cells from Rathke’s Pouch in Chicken (Gallus gallus) and Japanese Quail (Coturniz coturniz japonica). Expression of Calcium‐Binding Proteins

“…The development of the hypophysis in birds has been studied by several authors (Wingstrand, 1951, 1966) although most point to an exclusively ectodermic origin from RP, in Japanese quail we observed the participation of SP, of endodermic origin in the morphogenesis of the rostral part of the adenohypophysis. There are studies on some species that refer to the participation of SP in morphogenesis of the adenohypophysis (Gorbman, 1983; Hall and Hughes, 1985), nevertheless in most vertebrate species it has not been observed to participate.…”