Chromatin Studies Of Schistosomes

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The schistosomes are a unique family among the trematodes in that they are fully dioecious. Several species are important human pathogens, and cytological characterization of their chromosomes was attempted as a direct means of species identification.;Hypotonic pretreatment of asexually proliferative schistosome tissue facilitated identification of centromere locations through the spreading apart of sister chromatids. A fixation procedure was developed which prevented the overextraction produced by conventional acetic methanol fixation. Permanent preparations were made which were suitable for cytological manipulations over a period of several months.;In efforts to identify late-replicating chromatin and to time cercarial development in schistosomes, the use of ('3)H-thymidine produced anomalous results which implied that this radioactive probe has deleterious effects upon the nuclear cycle. Autoradiographs of embryonic cells revealed incorporation of ('3)H-thymidine into interphase nuclei, but labeled nuclei beyond prophase could not be identified. Label incorporation in the small dense nuclei of cercarial embryos indicated that this distinctive morphology is not due to a presynthetic stage of the cell cycle.;Standard methods of mammalian chromosome banding had deleterious effects on the schistosome chromosomes. Strong banding was not achieved with attenuated protocols, but a few staining patterns were identified. The unique response of schistosome chromosomes to methods for demonstration of cytological markers in higher eukaryotes, e.g. silver nitrate staining of the nucleolar organizer region and in situ hybridization with ('3)H-rRNA, emphasize that this system departs from the karyological behavior of higher eukaryotes.;Cytological analysis of the nature of cercarial nuclei indicates that the intense staining of tail nuclei with Giemsa is derived from a major proteinaceous component, which is removable with trypsin. The small dense nuclei of early embryos--classically identified as the germinal lineage--are strongly Feulgen-positive and highly fluorescent with acridine orange and quinacrine; these nuclei are resistant to treatment with acid, base, DNase and trypsin, but their extraction in hot salt solution reveals that a salt-soluble, nonhistone protein is an integral component. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI

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