Establishment of cellular polarity is one of the key events during oocyte maturation. Inscuteable (Insc) has been identified as a key regulator of cell polarity during asymmetric division in Drosophila. However, the function of its evolutionarily conserved mammalian homologue, mInscuteable (mInsc), in mouse meiotic maturation is not clear. In this study, we investigated the roles of mInsc in mouse oocyte maturation. mInsc was detected at all stages of oocyte maturation. The protein level of mInsc was slightly higher at the germinal vesicle breakdown (GVBD) stage and remained constant during mouse oocyte maturation. The subcellular localization of mInsc overlapped with spindle microtubules. Disruption of microtubules and microfilaments caused changes in the localization of mInsc. Depletion or overexpression of mInsc significantly decreased the maturation rates of mouse oocytes. Depletion of mInsc significantly affected asymmetric division, spindle assembly, alignments of chromosomes and actin cap formation. Taken together, our results demonstrated that mInsc regulates meiotic spindle organization during mouse meiotic maturation.

The ultrastructural analysis of human oocytes at different maturation stages has only been descriptive. The aim of this study was to use a stereological approach to quantify the distribution of organelles in oocytes at prophase I (GV). Seven immature GV oocytes were processed for transmission electron microscopy and a classical manual stereological technique based on point-counting with an adequate stereological grid was used. The Kruskal–Wallis test and Mann–Whitney U-test with Bonferroni correction were used to compare the means of the relative volumes occupied by organelles in oocyte regions: cortex (C), subcortex (SC) and inner cytoplasm (IC). Here we first describe in GV oocytes very large vesicles of the smooth endoplasmic reticulum (SER), vesicles containing zona pellucida-like materials and coated vesicles. The most abundant organelles were the very large vesicles of the SER (6.9%), mitochondria (6.3%) and other SER vesicles (6.1%). Significant differences in organelle distribution were observed between ooplasm regions: cortical vesicles (C: 1.3% versus SC: 0.1%, IC: 0.1%, P = 0.001) and medium-sized vesicles containing zona pellucida-like materials (C: 0.2% versus SC: 0.02%, IC: 0%, P = 0.004) were mostly observed at the oocyte cortex, whereas mitochondria (C: 3.6% versus SC: 6.0%, IC: 7.2%, P = 0.005) were preferentially located in the subcortex and inner cytoplasm, and SER very large vesicles (IC: 10.1% versus C: 0.9%, SC: 1.67%, P = 0.001) in the oocyte inner cytoplasm. Further quantitative studies are needed in immature metaphase-I and mature metaphase-II oocytes, as well as analysis of correlations between ultrastructural and molecular data, to better understand human oocyte in vitro maturation.

The development of auxospores and initial cells of the freshwater chain-forming diatom Ellerbeckia arenaria forma arenaria was studied using light and electron microscopy. Whether the auxospore mother cell is formed vegetatively (parthenogenesis) or through autogamy is still a matter for speculation. Because no signs of spermiogenesis could be detected in our material, we exclude oogamy. Further development involves retraction of the protoplast from the epivalve and the formation of a featureless siliceous cap with a central opening on its free surface. The homology and function of this cap remain uncertain. At the other end of the cell the protoplast remains tightly attached to the hypovalve throughout its further development. This hypovalve always has a concave valve face. An organic wall bearing many layers of overlapping, small silica scales begins to be formed while the cell is still enclosed within the mother cell wall, and allows the auxospore to swell, thus breaking the siliceous cap and girdle bands. External and internal surfaces of scales can be distinguished morphologically. Initial valves are formed internal to the scales at an oblique angle to the parent chain. The initial epivalve always faces the hypotheca of the auxospore mother cell, and the initial valves already show elements of the heterovalvy manifest in the vegetative cells. The significance of the observations in terms of ecology and phylogeny is discussed. The combinations Ellerbeckia arenaria (Moore ex Ralfs) R. M. Crawford, and E. arenaria forma teres (Brun ex Schmidt) R. M. Crawford are made.