RNA in Cecropia moth ovaries: Sites of synthesis, transport, and storage

Abstract

Azure B staining of Cecropia moth ovarian follicles indicated that the pattern of RNA concentrations characteristic of vitellogenic oocytes is disrupted by a gross redistribution and dispersion, beginning with the final discharge of the cytoplasm of the nurse cells into the oocyte. The cytoplasmic redistribution is largely complete two days later when chorion formation begins, the germinal vesicle breaks down, and the first meiotic spindle forms.At this stage the follicle contains 30 pg of RNA, of which 27 pg are in the follicle cells and only 3 p g in the oocyte itself. The proportionately large amount of follicle cell RNA apparently reflects the synthetic functions of these cells in the formation of yolk and the secretion of chorion. Of the 3 pg in the oocyte, only 1 pg is incorporated into the early embryo while the remainder is found in the yolk cells and serosa.Autoradiography of follicles labeled with H3-uridine either i n vivo or by a "pulsechase" procedure in vitro indicated that, as in other polytrophic insect ovaries, the nurse cell nuclei are the most conspicuous source of oocyte RNA. The germinal vesicle incorporated labeled uridine in previtellogenic follicles. In vitellogenic and later stages neither a germinal vesicle nor a follicle cell contribution to oocyte RNA was detected by the procedures used.In the large, yolky oocytes produced by most arthropods and lower vertebrates, cytoplasmic RNA originates primarily either in the lamp-brush chromosomes and multiple nucleoli of the germinal vesicle (Gall and Callan, '62; Davidson, Allfrey and Mirsky, '64; Brown, '66) or, as in several orders of insects, in the polyploid nuclei of a set of nurse cells which arise as mitotic siblings of the oocyte (King and Burnett, '59; Sirlin and Jacob, '60; Zalokar, '60; Bier, '63).While it once seemed plausible to assume that the RNA from these sources served primarily as the machinery for the synthesis of yolk, more recent developments have rendered any prejudgment concerning such a function uncertain. In both insects and vertebrates extraovarian tissues are now known to synthesize much of the yolk protein (Telfer, '54, '60; Knight and Schectman, '54; Wallace and Dumont, in press), and the intuitive demand that yolk deposition requires unusual amounts of RNA in the oocyte itself has accordingly diminished. At the same time an alternative function has become apparent with the finding that protein synthesis following fertilization in these eggs is SUP-J. EXP. ZOOL., 170: 1-24.ported by stable RNA's deposited in the oocyte during its development in the ovary (Brown and Littna, '64; Brown and Gurdon, '64; Smith and Ecker, '65; Lockshin, '66; Crippa, Davidson and Mirsky, '67).Sorting out the vitellogenic and embryogenic functions of oocyte RNA will require coordinated analysis of both the origins and classes of RNA and the synthetic functions it serves in the cytoplasm. Such an approach would seem particularly practical in the Cercropia moth, in which a study of the synthetic requirements of egg formation is al...

Optimization of conditions for in situ hybridization and determination of the relative number of ribosomes in the cells of the mature embryo sac of maize

“…In many insects the oocyte is cytoplasmically connected to polyploid nurse cells. Ribosomes synthesized in the nurse cells are transferred to the oocyte (Pollack and Telfer 1969;Hughes and Berry 1970;Telfer 1975;Davidson 1986). The mechanism(s) by which the very large numbers of ribosomes are synthesized by the cells of the embryo sac are unknown.…”

Specific Protein Synthesis in Cellular Differentiation

“…Finally, as the last step in their differentiation, they secrete a proteinaceous eggshell, the chorion, around the vitelline membrane . At maturity, the chorion accounts for approximately 30 0/0 of the dry weight of the egg (Pollack and Telfer, 1969) .…”

Large electrical currents traverse developing Ceropia follicles

“…Like follicles in earlier stages, these post-collapse follicles show a relatively large current entering their most anterior accessible point. By this stage, however, the anterior pole current enters a region over the shrunken remnants of the nurse cells, which are supposed to be disconnected from the oocyte (16,17). Moreover, as before, less intense currents leave most of the rest of the oocyte.…”

“…Moreover, the intensity of this forward current grows steadily as one moves forward, with much of the change occurring near the furrow. Thus it rises slowly from a density of 0.4 ,A/cm2 near the rear pole to 1 gA/cm2 at a point 80 ,gm behind the furrow, jumps to 6 ,gA/cm2 at a point 40 ,um in front of the furrow, then rises further to 17 ,iA/cm2 at the most forward point explored. Altogether, this tangential pattern is fully consistent with the inferences drawn from the normal one: current flows forward from the oocyte and furrow sources towards the nurse cell sinks; the forward current jumps near the furrow as current from the furrow joins it; it is quite concentrated and still rising en route to the inferred main sink at the front pole.…”