Graduate Thesis Or Dissertation
 

The incidence and development of somatic polyploidy in the marine isopod Idothea wosnesenskii

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  • (Brandt) were surveyed for the presence of polyploid cells. Large polyploid cells were found in the hepatic cecum, gut and sheath of the testis. The relative DNA content of the polyploid nuclei was measured by means of two wavelength cytophotometry. Histograms plotted from the data provide information on the level and range of the nuclear DNA, and on changes during the course of development. Nuclei from the adult hepatic cecum range from 32C to 256C and do not conform to discrete DNA multiples. In juveniles, the hepatic cecum nuclei vary from 16C to 64C. In emergers, however, they are arranged in distinct classes of 2C. 4C, and 8C nuclei. The incidence and development of ploidy in the midgut are similar to the hepatic cecum of both adults and juveniles. The hepatic cecum cells of newly emerged specimens, however, all have 2C nuclei. Nuclei of testis sheath cells form a doubling series corresponding to discrete nuclear classes. In adults, 75 percent of the nuclei are 16C, and the remainder 32C. A bimodal distribution is also found in juvenile specimens, but the DNA values are lower. The frequency of nuclei in each class shifts as the animals grow. Simultaneous measurements of nuclear volume and DNA content were made on nuclei of the hepatic cecum. It was found that the correlation between these two factors is high, enabling a reasonably accurate estimation of the nuclear DNA content from a measurement of the nuclear diameter. Autoradiographic evidence indicates that adult testis sheath nuclei continue to synthesize DNA, while adult hepatic cecum and midgut nuclei do not. In juvenile specimens, nuclei of all three tissues synthesize DNA. Cells of the hepatic cecum and midgut do not respond to crustecdysone, whether exposed in vitro or in vivo. Testis sheath cells, however, respond to the molting hormone when exposed in vitro.
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