Nucleolar cycle and its correlation with chromatoid bodies in the Tilapia rendalli (Teleostei, Cichlidae) spermatogenesis.

The aim of this study was: (1) to monitor the nucleolar material distribution using cytological and cytochemical techniques and ultrastructural analysis; and (2) to compare the nucleolar material distribution with the formation of the chromatoid body (CB) in the germ epithelium of Tilapia rendalli. Nucleolar fragmentation occurred during the leptotene of prophase I and nucleolus reorganization occurred in the early spermatid nucleus. The area of the early spermatid nucleolus was significantly smaller than that of the spermatogonia nucleolus. Ultrastructural analysis showed an accumulation of nuages, which form the CB, before nucleolar fragmentation in the spermatogonia cytoplasm. The CB was observed in association with mitochondrial clusters in the cytoplasm of primary spermatocytes, as well as in those of initial and later spermatids. In conclusion, the nucleolus seems to be related to CB formation during spermatogenesis of T. rendalli, because at the moment of nucleolus fragmentation in the primary spermatocytes, the CB reaches its largest area and it is able to complete important functions during spermatogenesis. The reorganized nucleolus of the initial spermatids has a lower area due several factors, one of which is the probable migration of nucleolar fragments from the nucleus to the cytoplasm, therefore playing a role in CB formation.

Asynchronous meiosis in an interspecific hybrid of Brachiaria ruziziensis and B. brizantha.

Male meiosis is generally synchronous in higher plants. The regulation of the cell cycle is still not well understood, and a powerful tool for gaining an understanding of this regulation is the development of mutations that affect cell-cycle synchrony. We report here asynchronous microsporogenesis in an interspecific hybrid between two important tropical grasses. In young spikelets of the interspecific hybrid 49.10% of anther meiocytes entered meiosis, exhibiting typical phases of the first and second divisions, while the other 50.90% showed distinctive features of early prophase. In older spikelets, anthers containing mature pollen grains also displayed meiocytes still undergoing meiosis. At this time, the latter cells were enclosed by the exine wall. Despite asynchrony, all cells completed meiosis. Old anthers contained only pollen grains that appeared to be in the same stage of development. Pollen fertility was estimated to be 52.76% in dehiscent anthers. An independent genetic control for meiosis synchrony and meiotic stages is suggested.

Hydrogenosome behavior during the cell cycle in Tritrichomonas foetus.

The hydrogenosome is an unusual organelle found in several trichomonad species and other protists living in oxygen poor or anoxic environments. The hydrogenosome behavior in the protist Tritrichomonas foetus, parasite of the urogenital tract of cattle, is reported here. The hydrogenosomes were followed by light and transmission electron microscopy during the whole cell cycle. Videomicroscopy, immunofluorescence microscopy, and immunocytochemistry were also used. It is shown that the hydrogenosomes divide at any phase of the cell cycle and that the organellar division is not synchronized. During the interphase the hydrogenosomes are distributed mainly along the axostyle and costa, and at the beginning of mitosis migrate to around the nucleus. Three forms of hydrogenosome division were seen: (1). segmentation, where elongated hydrogenosomes are further separated by external membranous profiles; (2). partition, where rounded hydrogenosomes, in a bulky form, are further separated by a membranous internal septum and, (3). a new dividing form: heart-shaped hydrogenosomes, which gradually present a membrane invagination leading to the organelle division. The hydrogenosomes divide at any phase of the cell cycle. A necklace of intramembranous particles delimiting the outer hydrogenosomal membrane in the region of organelle division was observed by freeze-etching. Similarities between hydrogenosomes and mitochondria behavior during the cell cycle are discussed.