A Comparative Study of Adrenal Gland Development in Mouse and Chick Embryos

Ba-Omar, Taher A. O (1989) A Comparative Study of Adrenal Gland Development in Mouse and Chick Embryos. PhD thesis, University of Glasgow.

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In this work, I describe in detail the development of cellular patterns in mouse and chick adrenals, in an attempt to discover the morphogenetic mechanisms that produce these patterns. Mouse adrenal gland tissues (chromaffin and cortical) are intermingled during embryonic life, but sort-out near the end of gestation into a central mass (medulla) of chromaffin tissue and a surrounding cortex. Once sorting out has occurred, the cells assemble into cortical zones and medullary cords. Chick adrenal gland tissues (chromaffin and cortical) are intermingled with each other during embryonic and post-hatching life. In mouse, the zona glomerulosa develops at day 1 and by day 4 both zona glomerulosa and fasciculata are obvious. By the end of the first week postnatal the cortex possesses three zones: zona glomerulosa, fasciculata and the developing X-zone. X-zone cells start to appear on the 4th day postnatal. The zona reticularis starts to develop while the X-zone is degenerating, about 32 days postnatal. An inner capsule is formed between the medulla and cortex of the male adrenal by 35 days postnatal (this process occurs later in females, during first pregnancy). Chromaffin cells start to be arranged in groups by 4 days postnatal and assume their final position in the centre of the gland (medulla) by 7 days postnatal. Different iation of chromaffin cells into A and NA cell types takes place in postnatal life. In chick, light and dark cortical cells are seen from 15 days of incubation up to and including 19 days. Zonation of cortical tissues is not seen. Differentiation of chromaffin cells into A and NA cell types takes place during post-hatching life. Sympathetic ganglion cells may contribute to the increased number of chromaffin cells by means of differentiation. At TEM level the cell surface of mouse adrenal tissues is smooth with little sign of elongated cellular processes, throughout the period when sorting out of the tissue types is occurring. Some elongated cells are seen during sorting out stages, but not later. The cell surfaces of chick adrenal cells were similar, but were not studied during stages when significant cell sorting was occurring. No obvious changes occur with respect to cell junctions (between like and unlike cells) in all stages studied in both mouse and chick adrenals. The distribution of fibronectin was analysed in embryonic mouse and chick by means of immunofluorescent labelling. Fibronectin was found in both mouse and chick embryonic adrenals at all stages studied, within the capsule, within blood vessels, around and between cortical cells, but only around groups of chromaffin cells, not within groups. There was no evidence for any quantitative variation in fibronectin that might have created an adhesive gradient to guide cell movement. An unexpected results of this work was the discovery of cell death in both cortical and chromaffin tissues in embryonic adrenals of mouse and chick. These findings have not been reported before. Morphometric analysis showed that mouse cortical tissue grows more rapidly than chromaffin during embryonic life and that mitosis is higher among corticals than chromaffins. It showed also that the medulla does not always form precisely in the centre of the gland. In a final discussion chapter, I consider the role of cell death in the embryonic adrenal, and suggest this may be to maintain a loose enough structure to allow active cell sorting. This chapter also discusses the possible mechanisms of cell sorting and concludes that the most likely process to be involved is differential adhesion. Suggestions are also made for further work on adrenal morphogenesis.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Developmental biology, Endocrinology
Date of Award: 1989
Depositing User: Enlighten Team
Unique ID: glathesis:1989-77947
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:47
Last Modified: 30 Jan 2020 15:47
URI: https://theses.gla.ac.uk/id/eprint/77947

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