Role of pyriform cells during the growth of oocytes in the lizard Podarcis sicula

Abstract

In order to clarify the role of follicle cells during growth of previtellogenic oocytes in lizards, an ultrastructural and autoradiographic investigation was carried out in Podarcis sicula. The evidence obtained clearly indicated that both intermediate and pyriform cells are actively involved in the synthesis of RNA that is then transferred to the oocyte, via intercellular bridges, apparently together with a variety of cytoplasmic organelles. At the end of the previtellogenic phase of growth, during the regression of the epithelium, the rate of synthesis of RNA in follicle cells is reduced, in particular in the nucleolus, but the flow of materials toward the oocyte continues. Thus, the intermediate and pyriform cells should be regarded as nurse cells even though they have characteristics rather different from those of the nurse cells described in other animals, such as insects. 0 1995 Wiley-Liss, Inc.

Local Gene Expression in Axons and Nerve Endings: The Glia-Neuron Unit

“…Together with the previous data (62,229,265), the above results provide convincing evidence that the transfer of glia-synthesized RNA into the axoplasmic domain is modulated by axonglia communication (92,117). Comparable cell-to-cell RNA transfer takes place in different eukaryotic cells, such as the follicular cells and the oocytes of insects and reptiles (29,217,238).…”

“…Such a tightly paired association of neuron size with perineuronal glial number suggests that one of the major factors of this striking outcome regards the multiplication of glial genomes. A comparable multiplication at a genomic scale occurs in the follicular cells of developing oocytes (217,238). It may be noted that the role played by multiple sets of cell genomes may not be substantially dissimilar from the amplification of more restricted DNA regions, except for the global extent of its trophic potential.…”

“…Most likely, the underlying mechanisms may be different in different systems. Starting with the cytoplasmic bridges joining the follicular cells and the oocyte (217,238) or glial cells and crayfish axons (253), a number of different mechanisms have been proposed. They include an invagination of glial cytoplasm into the axon followed by pinching off and engulfment of the glial invagination (103,195), or a combined process of trans-endocytosis leading to the formation of spinules (288).…”

“…Dendrites are known to import RNA from the neuron cell body rather than exporting it to the perikaryon, or even less likely to the neuronal nucleus. This early criticism appears to have been largely based on the lack of information on intercellular exchanges of materials, which is now well known to occur in eukaryotic cells, such as follicular cells and oocytes (217,238). The data supporting intercellular transport of glial RNA to the neuron soma have also been corroborated by cytospectrophotometric methods that may hardly be blamed for confusing a glial cell with a dendrite (260,261).…”

Previtellogenesis in Antarctic fishes: Comparison with temperate species

“…Two specimens of T. bernacchii were fixed in SPAF (2 g paraformaldehyde + 15 ml picric acid + 31 g sucrose in 100 ml distilled water), processed for embedding in Epon 812 (Reynolds, 1963) and examined by electron microscopy. Ultrathin sections were stained with uranyl acetate and lead citrate and observed using a Philips 301 microscope (Motta et al, 1995). All reagents were purchased from Sigma (Sigma Ltd, Milano, Italy).…”