Oocyte structure and ultrastructure in the Mexican silverside fish Chirostoma humboldtianum (Atheriniformes: Atherinopsidae)

the structural and ultrastructural features of gonads from endemic Mexican fish have received scarce attention. This study describes the histological and ultrastructural characteristics of the oocyte in Chirostoma humboldtianum. The ovary is asynchronic, and as such, most phases of oocyte development are found in the same ovary. The complete process of oogenesis was divided in five stages: oogonium and folliculogenesis, primary growth, cortical alveoli and lipid inclusions, vitellogenesis and maturation. The presence of big filaments, which appear at the end of primary growth, induces some common follicular adaptation. During primary growth, abundant ribosomes, rough endoplasmic reticulum, and mitochondria are grouped in the cytoplasm. At the end of this stage, the Z1 layer of the chorion is developed, while microvilli start to be evident as well. In the cortical alveoli and lipid droplets phase, intense PAS positive vesicles, some of them containing nucleoid material, are observed in the peripheral cytoplasm and the lipid droplets take a more central position. In vitellogenesis, the proteic yolk accumulates in a centripetal way while the chorion is completely formed. In maturation, the germinal vesicle migrates to the animal pole, meiosis is restored, and there is nuclear breakdown. The oocyte increases its size and holds some oil droplets and a big fluid mass of yolk. On the outside, filaments surround the oocyte completely. Rev. Biol. Trop. 56 (4): 1825-1835. Epub 2008 December 12.

Los aspectos estructurales y ultraestructrurales de las gónadas de peces mexicanos endémicos han sido poco estudiados. En el presente trabajo reportamos las características histológicas y ultraestructurales del ovocito de Chirostoma hulmboldtianum. El ovario es de tipo asincrónico, por ende, la mayoría de las fases del desarrollo del ovocito pueden ser encontradas en el mismo ovario. El desarrollo del ovocito fue dividido en cinco etapas: ovo-gonia y foliculogénesis, crecimiento primario del ovocito, inclusiones lipídicas y gránulos corticales, vitelogénesis y maduración. La presencia de grandes filamentos que aparecen al final de la etapa de crecimiento primario, inducen adaptaciones foliculares. Durante el crecimiento primario, en el citoplasma se encuentran abundantes ribosomas, retículo endoplásmico rugoso y agrupamientos de mitocondrias. Al final de esta etapa, inicia el desarrollo de la capa Z1 del corion, comenzando a ser evidentes las microvellosidades del ovocito. Durante la etapa de inclusiones lipídicas y gránulos corticales, vesículas PAS positivas, algunas de ellas con material nucleoide, se ubican en la periferia del ovocito, mientras que las que contienen material graso toman una posición más central en la célula. Durante la vitelogénesis se presenta una acumulación de vitelo protéico en un sentido centrípeto; durante esta etapa, el corion está completamente formado. En la maduración, la vesicular germinal migra hacia el polo animal, se reinicia la meiosis y se rompe la envoltura nuclear. El ovocito incrementa su tamaño y en el citoplasma se pueden observar algunas gotas de grasa y el vitelo se presenta como una gran masa acuosa. En el exterior, los filamentos rodean completamente al ovocito.

Localization of intranuclear RNA by electron microscopy in situ hybridization using a genomic DNA probe

Background. The presence of RNA in the cell nucleus is well known. However, a high resolution in situ hybridization evidence for the presence of RNA in some nuclear particles is still lacking. The aim of this work is to localize RNA in subnuclear particles using a novel ultrastructural in situ hybridization procedure. In this study, biotinylated genomic mouse DNA as a probe to localiza total RNA in the nuclei of mouse hepatocytes was used. Methods. The procedure is based on Paraformaldehyde fixation and embedding in lowicryl resin. Thin sections are mounted in formvar-coated gold grids. Hybridization is performed on non-denatured thin sections. DNA-RNA hybrids are detected with streptavidin-10 mm gold particles complex. By controlling the time of nick-translation during incorporation of biotin into the probe, labeling in the fibrillar portions of the nucleoplasm is obtained. More digested probes generate more labeling in the granular components. Nucleoli were similarly labeled. Results. As expected, no label was observed in the compact chromatin clumps. These results indicate that granular components as perichromatin granules in the nucleus contain more processed RNA than fibrillar portions. As a comparison, viral DNA sequences on denatured RNase-treated thin sections of adenovirus-2 (Ad-2)-infected human cells were detected. As previously reported, at late stages DNA was observed in the viral particles and surrounding nucleoplasm, where Ad-2 DNA is synthesized. Conclusions. The present procedure allows the study of intranuclear RNA distribution and will be useful fo the analysis of RNA processing in several types of cells