Abstract:The mitochondrial population of sustentacular cells in the testis of the amphibian, Xenopus laevis, has been examined by electron microscopy. Three distinct types of mitochondria have been observed. The first and most common mitochondrial type is a "typical" organelle with a rod-like profile containing tubular to plate-like cristae. The second mitochondrial form is characterized externally by irregular bulbous protrusions and internally by increased numbers of tubular cristae. The third mitochondrial type, whi… Show more
“…In the male gonad, the expression of SOX9 is first observed after metamorphosis and restricted to the somatic cells that support germ cells. In amphibians different nomenclatures have been used to designate these supporting cells: follicle cells (Lofts,1974; Sàez et al,1999,2004), follicular cells (Burgos et al, 1956; Chavadej et al,2000), sustentacular cells (Kalt et al,1975), and Sertoli cells (Penrad‐Mobayed,1983; Risley,1990; Risley and Morse‐Gaudio,1992). Our ultrastructural study shows that these supporting cells exhibit several of the morphological characteristics of mammalian Sertoli cells, such as a close association with the developing germ cells and the presence of ectoplasmic specializations that are formed by tight junctions and parallel‐arranged laminae of r‐ER (Meyer et al,1977).…”
To investigate the role of SOX9 gene in amphibian gonadogenesis, we analyzed its expression during male and female gonadogenesis in Xenopus tropicalis. The results showed that in both sexes SOX9 mRNA and protein were first detectable after metamorphosis when the gonads were well differentiated and remained present until the adult stage. In the testis, SOX9 expression was restricted to the nucleus of Sertoli-like cells, similarly to what has been observed in other vertebrates suggesting a conserved role in vertebrate testicular differentiation. In the ovary, in sharp contrast with what has been observed in all vertebrates examined so far, the SOX9 protein was localized in the cytoplasm of previtellogenic oocytes before being translocated into the nucleus of vitellogenic oocytes suggesting an unexpected role during oogenesis. These results suggest that the SOX9 gene may not be a sex-determining gene in X. tropicalis and may play different functions in testicular and ovarian differentiation. Developmental Dynamics 237:2996 -3005, 2008.
“…In the male gonad, the expression of SOX9 is first observed after metamorphosis and restricted to the somatic cells that support germ cells. In amphibians different nomenclatures have been used to designate these supporting cells: follicle cells (Lofts,1974; Sàez et al,1999,2004), follicular cells (Burgos et al, 1956; Chavadej et al,2000), sustentacular cells (Kalt et al,1975), and Sertoli cells (Penrad‐Mobayed,1983; Risley,1990; Risley and Morse‐Gaudio,1992). Our ultrastructural study shows that these supporting cells exhibit several of the morphological characteristics of mammalian Sertoli cells, such as a close association with the developing germ cells and the presence of ectoplasmic specializations that are formed by tight junctions and parallel‐arranged laminae of r‐ER (Meyer et al,1977).…”
To investigate the role of SOX9 gene in amphibian gonadogenesis, we analyzed its expression during male and female gonadogenesis in Xenopus tropicalis. The results showed that in both sexes SOX9 mRNA and protein were first detectable after metamorphosis when the gonads were well differentiated and remained present until the adult stage. In the testis, SOX9 expression was restricted to the nucleus of Sertoli-like cells, similarly to what has been observed in other vertebrates suggesting a conserved role in vertebrate testicular differentiation. In the ovary, in sharp contrast with what has been observed in all vertebrates examined so far, the SOX9 protein was localized in the cytoplasm of previtellogenic oocytes before being translocated into the nucleus of vitellogenic oocytes suggesting an unexpected role during oogenesis. These results suggest that the SOX9 gene may not be a sex-determining gene in X. tropicalis and may play different functions in testicular and ovarian differentiation. Developmental Dynamics 237:2996 -3005, 2008.
“…A practically unambiguous identification of projections of all members of all three families of cubic membranes have been performed in manifold cases reporting various, hitherto perplexing membrane morphologies [1]. These are exemplified by a SER G-type of single balanced cubic membrane [8], an unbalanced plasma G-type membrane [9], a multicontinuous mitochondrial G-type [10], a single balanced D-type in mitochondria [11], the unbalanced D-type of the prolamellar body (PLB) [1], a SER multicontinuous D-type [12], an intranuclear single membrane balanced P-type [13], the unbalanced P-type [14], and, finally, a mitochondrial multicontinuous P-type cubic membrane [15]. The lattice parameter of a cubic membrane seems to be highly controlled, and is often maintained constant within a certain cell type at a given time.…”
The identification of evolutionary conserved membrane morphologies whose architecture is governed by cubic symmetry -cubic membranes -adds a new dimension to cell membrane functions and, perspicuously, to their role in subcellular space organization. Through analysis of electron micrographs, three families of cubic membranes have been unequivocally identiffed in which one or more (parallel) membranes, described by periodic cubic surfaces, partition space into two or more independent, albeit convoluted, subspaces of membrane potential determined dimensions. The choice of a particular cubic symmetry is suggested to be due to its activity. Here the architecture and function of multiple (---3) subspace organization in classical membrane bound organelles is addressed. As it can be precisely determined with cubic membranes suggests that they can be employed as a reference morphology.
“…Some examples of extraordinary shapes of mitochondrial cristae can be found (e.g. [ 19 – 24 ]). Figure 1 Mitochondrial cristae have varied morphologies.…”
Mitochondria are complex organelles with two membranes. Their architecture is determined by characteristic folds of the inner membrane, termed cristae. Recent studies in yeast and other organisms led to the identification of four major pathways that cooperate to shape cristae membranes. These include dimer formation of the mitochondrial ATP synthase, assembly of the mitochondrial contact site and cristae organizing system (MICOS), inner membrane remodelling by a dynamin-related GTPase (Mgm1/OPA1), and modulation of the mitochondrial lipid composition. In this review, we describe the function of the evolutionarily conserved machineries involved in mitochondrial cristae biogenesis with a focus on yeast and present current models to explain how their coordinated activities establish mitochondrial membrane architecture.
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