Abstract
The ultrastructure of the follicular wall in primordial, previtellogenic and vitellogenic follicles of the sexually immature ostrich is described in the present study. The follicular wall consists of a zona radiata, granulosa cell layer, basal lamina and thecal layer. Cytoplasmic processes from the plasma membranes of the granulosa cell layer and the ovocyte form the zona radiata in previtellogenic and vitellogenic follicles. The granulosa cell layer transforms from simple cuboidal epithelium in primordial follicles to simple columnar or pseudostratified columnar epithelium in previtellogenic and vitellogenic follicles. Transosomes were observed along the apical and lateral plasma membranes of granulosa cells. The thecal layer in previtellogenic and vitellogenic follicles consists of interna and externa components. The fibroblasts in the theca externa contain microfilaments, which are thought to be actin filaments. The study revealed ultrastructural features, which are associated with the transportation of yolk precursors and nutrients into the ovoplasm. In addition, the study indicates that, although the cells in the theca externa contain microfilaments, they do not possess the ultrastructural characteristics of smooth muscle cells.
Highlights
IntroductionAccepted for publication 6 April 2006—Editor quail (Ito, Kihara, Nakamura, Yonezawa & Yoshizaki 2003)
The follicular wall enclosing the ovocyte was composed of four layers: the zona radiata; granulosa cell layer; basal lamina and thecal layer
Based on the structure of the follicular wall it is evident that its primary function is the transportation of yolk precursors to the ovocyte
Summary
Accepted for publication 6 April 2006—Editor quail (Ito, Kihara, Nakamura, Yonezawa & Yoshizaki 2003). These studies have highlighted marked developmental changes in the ultrastructure of the zona radiata, perivitelline, granulosa and thecal components of the follicular wall. The precocious development of the ovary and oviduct in the sexually immature ostrich has been described (Madekurozwa 2002a, b, 2004, 2005). A more recent histological and immunohistochemical study demonstrated the presence of primordial, previtellogenic and vitellogenic developing follicles in the active ovary of the sexually immature ostrich (Madekurozwa & Kimaro in press). Primordial follicles are composed of an oocyte surrounded by a layer of flat granulosa cells. The granulosa cells are enclosed in a single layer of squamous thecal cells
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