Germline cysts and asymmetry in early previtellogenic ovarian follicles in cultured albino females of sterlet Acipenser ruthenus L. 1758 (Chondrostei, Acipenseriformes)

Abstract

It is a first report on the structure of germline cells in ovaries of albino sterlet Acipenser ruthenus L. 1758. Ovarian nests, follicles, and germinal epithelium have been examined in gynogenetic and control specimens of this species. The structure of oogonia (named the cystoblasts) and of germline cysts in the nests has been described in detail. Also, the asymmetry in the cytoplasm and early growth of cystocytes in the cysts and of early previtellogenic oocytes has been described. In the cytoplasm of cystoblasts and in all cystocytes, a precursor of granular cytoplasm (Balbiani cytoplasm) is present and defines future vegetal region in the oocytes. Interestingly, the nuclei in cystoblasts comprise a large dense body that contains deoxyribonucleic acid (DNA). The role of this body in formation of multiple nucleoli has been explained. During the zygotene and pachytene stages, massive extrachromosomal amplification of DNA begins in the nucleoplasm of all cystocytes. As a result of the accumulation of extra DNA, an irregularly shaped DNA-body is formed. Multiple nucleoli arise in this DNA-body and around fragments of dense bodies. The asymmetry of the early previtellogenic oocyte cytoplasm is well marked by the presence of the granular cytoplasm. Moreover, the cisternae of the rough endoplasmic reticulum, dictyosomes, mitochondria, complexes of mitochondria with cement, nuage accumulations, and lipid droplets are located in specific zones in the granular cytoplasm. The follicular epithelium is composed of two subpopulations of somatic follicular cells (FCs): the main body cells and future micropylar cells.

Asymmetry in the cytoplasm of oocytes of largescale yellowfish Labeobarbus marequensis Smith 1841 (Teleostei: Cypriniformes: Cyprinidae)

“…Similar morphological changes in the nucleoplasm were observed in previtellogenic oocytes (diplotene stage) of the related species, C. carpio (Mazzoni et al, 2010) and B. barbus (Thiry & Poncin, 2005), as well as in the ovarian nests and follicles of sturgeons: A. gueldenstaedtii , A. ruthenus and A. baerii (Raikova, Steinert, & Thomas, 1979; Żelazowska & Fopp‐Bayat, 2017, 2019). In B. barbus and in sturgeons, such fibrillar material is comprised of DNA and represents extrachromosomal amplified ribosomal DNA (rDNA) containing amplified ribosomal genes (Raikova et al, 1979; Thiry & Poncin, 2005; Żelazowska & Fopp‐Bayat, 2017, 2019). It is likely that the fibrillar material in nucleoplasm of primary growth oocytes of L. marequensis may also contain rDNA cistrons.…”

“…In ooplasm of M. salmoides the lysosome‐like organelles were also described, but in their formation vesicles of the rough ER and vesicles that are released by the trans‐cisternae of Golgi apparatus are involved (Żelazowska & Halajian, 2019). The close contact between the ER and mitochondria has been described in a great diversity of animal species as sturgeons: the Russian A. gueldenstaedtii (Zelazowska, Kilarski, Bilinski, Podder, & Kloc, 2007), and A. ruthenus (Żelazowska & Fopp‐Bayat, 2019), a mouse Mus musculus (Kloc et al, 2008), and a common cellar spider Pholcus phalangioides (Jędrzejowska & Kubrakiewicz, 2007). Multilamellar bodies present in oocytes of L. marequensis during Stage 2 possibly serve as organelles in which membranes necessary to increase the size of oocytes are stored.…”

“…The Bb is assembled in contact with the centrosome, which means that it forms in the close vicinity of the outer nuclear membrane and to its side that faces intercellular bridge connecting two differentiating oocytes. Germline cysts are also polarized in developing ovaries of the immature specimens of the Siberian sturgeon Acipenser baerii and in the sterlet A. ruthenus (Żelazowska & Fopp‐Bayat, 2017, 2019).…”

Diversity of Balbiani body formation in internally and externally fertilizing representatives of Osteoglossiformes (Teleostei: Osteoglossomorpha)

“…During oogenesis, we noted a sequence of germ plasm accumulations (Figure 11), partly similar to those described in Xiphophorus helleri by Azevedo (1984). The germ plasm is formed just under the nuclear envelope after passing through the nuclear envelope as small aggregations of electron‐dense material as in P. buchholzi , O. bicirrhosum (this study) and many other fish species (Grier, 2000, 2012; Żelazowska et al, 2007; Żelazowska & Fopp‐Bayat, 2019; Żelazowska & Halajian, 2019; Żelazowska & Kilarski, 2009) or as irregularly shaped electron‐dense material, which was observed in A. gigas (this study) and in X. helleri (Azevedo, 1984). Germ plasm accumulations are visible in ooplasm in close contact with mitochondria.…”

“…Germ plasm accumulations are visible in ooplasm in close contact with mitochondria. This phenomenon was often described in the oocytes of various species (Azevedo, 1984; Grier, 2000, 2012; Żelazowska et al, 2007; Żelazowska & Fopp‐Bayat, 2019; Żelazowska & Halajian, 2019; Żelazowska & Kilarski, 2009). In all three studied osteoglossiforms, the germ plasm is present between mitochondria within the mitochondrial network.…”