Possible participation of mitochondria in lipid yolk formation in oocytes of paddlefish and sturgeon

Abstract

The ovary of paddlefish and sturgeons (Acipenseriformes) is composed of discrete units: the ovarian nests and ovarian follicles. The ovarian nests comprise oogonia and numerous early dictyotene oocytes surrounded by somatic prefollicular cells. Each ovarian follicle consists of a spherical oocyte and a layer of follicular cells situated on a thick basal lamina, encompassed by thecal cells. The cytoplasm of previtellogenic oocytes is differentiated into two distinct zones: the homogeneous and granular zones. The homogeneous cytoplasm is organelle-free, whereas the granular cytoplasm contains numerous organelles, including mitochondria and lipid droplets. We have analyzed the cytoplasm of early dictyotene and previtellogenic oocytes ultrastructurally and histologically. In the cytoplasm of early dictyotene oocytes, two morphologically different types of mitochondria can be distinguished: (1) with well-developed cristae and (2) with distorted and fused cristae. In previtellogenic oocytes, the mitochondria of the second type show various stages of cristae distortion; they contain and release material morphologically similar to that of lipid droplets and eventually degenerate. This process of mitochondrial transformation is accompanied by an accumulation of lipid droplets that form a single large accumulation (lipid body) located in the vicinity of the oocyte nucleus (germinal vesicle). The lipid body eventually disperses in the oocyte center. The possible participation of these mitochondria in the formation of oocyte lipid droplets is discussed.

Ovarian nests in cultured Russian sturgeon Acipenser gueldenstaedtii and North American paddlefish Polyodon spathula comprised of previtellogenic oocytes

“…They were present in several ovarian nests in the ovaries of both species. The main difference between EP 1 oocytes described in this study and the early previtellogenic oocytes previously described (identically referred to as the early stage 1 previtellogenic oocytes, Żelazowska & Kilarski, ) was that all oocytes developed in ovarian nests [Fig. (b), (d)] and not within the ovarian follicles.…”

“…In the ovarian nests of both A. gueldenstaedtii and P. spathula , early previtellogenic oocytes (previously termed the early dictyotene oocytes, Żelazowska & Kilarski, ) were located [Fig. ].…”

“…The cystoblasts divided by mitoses to produce cysts (Quagio‐Grassiotto et al , ). Structures similar to germ cell nests were also present in the ovaries of sexually immature sturgeons and in the North American paddlefish Polyodon spathula (Walbaum 1792), and were termed ovarian nests (Żelazowska & Kilarski, ).…”

Ultrastructural observation on genesis and morphology of cortical granules in Macrobrachium nipponense (Crustacea, Caridea)

“…Also, the mitochondria of L. vannamei become the compartments for the contents of yolk granules through a similar process of phagocytosis. In addition, the research indicated similar transformation of mitochondria participation in yolk formation (Weakley, 1976;Pfannenstiel and Grunig, 1982;Thiaw and Mattei, 1992;Reunov et al, 2000;Zelazowska and Kilarski, 2009). Whether mitochondria, like vitellogenesis, are involved in the formation of cortical granules may require further study apart from TEM technique, however, we suggest that it is possible that some organelles, like mitochondria, take part in the origin of cortical granules.…”

Detection of SNPs in the Cathepsin D Gene and Their Association with Yolk Traits in Chickens

“…Yolk formation involves cholesterol uptake and transport mediated by the very low-density lipoprotein receptor on the membrane, and CTSD is the key enzyme in this process [17], [18]. Thus, it has been suggested that CTSD may be a candidate gene associated with egg yolk quality traits.…”