RESUMO
In mammals and flies, only one cell in a multicellular female germline cyst becomes an oocyte, but how symmetry is broken to select the oocyte is unknown. Here, we show that the microtubule (MT) minus end-stabilizing protein Patronin/CAMSAP marks the future Drosophila oocyte and is required for oocyte specification. The spectraplakin Shot recruits Patronin to the fusome, a branched structure extending into all cyst cells. Patronin stabilizes more MTs in the cell with the most fusome material. Our data suggest that this weak asymmetry is amplified by Dynein-dependent transport of Patronin-stabilized MTs. This forms a polarized MT network, along which Dynein transports oocyte determinants into the presumptive oocyte. Thus, Patronin amplifies a weak fusome anisotropy to break symmetry and select one cell to become the oocyte.
Assuntos
Proteínas de Drosophila/metabolismo , Células Germinativas/fisiologia , Proteínas Associadas aos Microtúbulos/metabolismo , Oócitos/fisiologia , Animais , Anisotropia , Drosophila melanogaster , Dineínas/metabolismo , Feminino , Células Germinativas/ultraestrutura , Proteínas dos Microfilamentos/metabolismo , Centro Organizador dos Microtúbulos/metabolismo , Microtúbulos/metabolismo , Microtúbulos/ultraestrutura , Oócitos/ultraestrutura , Organelas/metabolismo , Organelas/ultraestruturaRESUMO
The essential amino acid requirement of cultured mammalian cells can be satisfied by 19 amino acid derivatives. This finding (a) confirms the results of animal nutritional studies and (b) identifies 19 essential amino acid derivatives and should permit the isolation of a new class of auxotrophic mutants. Five naturally occurring auxotrophic markers have been detected in this survey; namely, inability to utilize cystathionine and citrulline in Chinese hamster ovary (CHO) cells, inability to metabolize citrulline by HTC+hepatoma cells, and confirmation of Eagle's observation that KB cells can utilize homocystine in place of methionine or cystine and D-cystine in place of L-cystine.