Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Nuclei in the giant silk gland cells of Calpodes ethlius grow continuously to form highly branched, regionally characteristic shapes. These cells were studied in an attempt to correlate the arrangement of nuclear and cytoskeletons with nuclear shape.;Nuclear matrices, examined in situ by SEM, have filament meshworks with shapes similar to those of Feulgen stained nuclei. Isolated nuclear matrices, examined by TEM, have parallel filaments within the nuclear branches. Hoechst stained DNA has a similar alignment. Immunofluorescence microscopy indicated that, although extraordinary in shape, these nuclei have some of the same matrix antigens found in smaller, spherical nuclei. SDS-PAGE of the nuclear-associated (nuclear matrix) fraction revealed few polypeptides, including a nuclear isoform of actin (43 kD, pI 6.45). Nuclear branches label at their periphery with antibodies to actin and myosin and with rhodaminyl-phalloin which is specific for f-actin. The nuclear-associated fraction contains a lamina-like structure that binds heavy meromyosin and antibodies to actin and myosin. This suggests that actin and myosin are components of a layer at the nucleocytoplasmic boundary called the nuclear shell which may correspond to a cytoplasmic zone containing filaments associated with the nuclear envelope.;During larval moults, globules, which label with antibodies to actin, form in the cytoplasm. Similar globules co-isolate with the nuclear matrix fractions from moulting larvae and label with antibodies to actin, but not to nuclear matrix antigens. The globules may be reserves of g-actin for growth of the perinuclear actin shell.;Labelling of silk glands with rhodaminyl-phalloin shows cytoskeletal f-actin in parallel bundles around the lumen. The bundles dissociate when larval feeding stops during the moults, and the f-actin forms coats around vacuoles. After the moult, f-actin reforms in periluminal bundles. Regional differences exist in the density of these bundles. The greatest density occurs in the narrower anterior regions of the gland and may be correlated with the increased hoop stress resulting from the reduced luminal diameter. F-actin coated vacuole formation during larval moults occurs in all but the duct and green regions.;As the formation of cytoplasmic actin-coated vacuoles occurs, the f-actin in the nuclear shell maintains its location. Thus, two kinds of f-actin deployment take place concurrently within these cells.



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