Caracterização dos ciclos replicativos nas células foliculares e nutridoras no ovário de <i>Rhynchosciara americana</i> e perfil de expressão de ciclinas A e B.

Abstract

Study of the diptera Rhynchosciara americana has provided important information about chromosome biology, for it displays polytene chromosomes and gene amplification in different organs. Among the organs that possess cell cycle specializations, the ovary is one of the most interesting ones, showing unique characteristics, such as the synchronous development of follicles and the presence of a single giant nurse cell connected to the oocyte through a cytoplasmic channel. This organ gathers: meiosis in the oocyte, nurse cell with polyploidy followed by polyteny, and follicle cells in mitosis. Polyploid and polytene cells have extra copies of genomic DNA obtained via sequential cycles of S phase not followed by cell division, a process called endoreplication. Cell cycles are driven by the oscilation in the activation of different cyclin/CDK complexes. Studies have shown that Cyclin A acts in endoreplicating cells in Drosophila and Cyclin B inhibits endoreplicative cycles, inducing cell division. Thus, it is relevant to investigate the association between these cell cycle-regulating proteins and the endoreplication cycles that occur during the oogenesis of R. americana. Expression profiles of cyclins A and B were evaluated in the ovary via RT-PCR throughout the development. Thymidine nucleoside incorporation assays showed high proliferative activity in follicle cells to build the follicle and the end of endoreplicative activity in nurse cells of 4-day-old pupae. Protein immunolocalization in ovary at the stage of pupa has shown accumulation of Cyclin A in the cytoplasm of nurse cells and oocytes, and accumulation of Cyclin B in the cytoplasm and germinal vesicle of the oocyte, acting on meiosis mechanisms. The study of proteins related to cell cycle in this model is important for a better understanding of uncommon cell cycle in different insect organ.