A Massive System of Microtubules Associated with Cytoplasmic Movement in Telotrophic Ovarioles

The telotrophic ovary of Notonecta glauca glauca consists of 7 ovarioles. Each ovariole comprises, from front to rear, a terminal filament, a trophic region, a prefollicular region, and a series of 10-15 follicles of progressively increasing size The trophic region is largely syncytial and is made up of polyploid trophic nuclei packed around a central trophic core The cytoplasm of the trophic core is continuous with the cytoplasm of each oocyte through a system of trophic tubes. There is one trophic tube per oocyte. The trophic nuclei have large nucleoli. There are a few small nucleoli in the oocyte nuclei The cytoplasm of the trophic core, the trophic tubes, and the oocytes is rich in RNA. Autoradiographs of sections of ovarioles fixed 2 h after injection of [3H]uridine into animals show label over the trophic nuclei only. Eight-hour autoradiographs show heavy labelling of the trophic region and label over the front ends of the trophic tubes, but little label over the posterior regions of the tubes or the oocyte cytoplasm. Later autoradiographs mdicate that label gradually spreads backwards from the trophic core, along the trophic tubes, and progressively builds up in the oocyte cytoplasm These observations are thought to indicate synthesis of RNA in the trophic region and movement of RNA from the trophic core along the trophic tubes to the oocytes The trophic core and tubes show brilliant positive form birefringence with respect to their lengths. This birefringence can be reduced by keeping animals at 2 °C for 12 h, and eliminated by placing ovarioles in 1 % colchicine for 6 h. Electron micrographs of thin sections of ovarioles show that trophic core and tubes are densely and uniformly packed with ribosomes and microtubules The latter are lined up along the trophic tubes. There are about 30000 microtubules evident in a TS through a trophic tube 15µm wide. Lengths of microtubules up to 2µm have been observed. Ribosomes are packed between the microtubules but are excluded from regions where the spacing between adjacent microtubules is less than 25 nm The contribution of the trophic region to the oocytes and the role of the microtubules in maintaining or facilitating the movement of ribosomes along the trophic tubes is discussed