Muzzopappa Mariana, Wappner Pablo
Instituto Leloir and IIB, FCEyN-Universidad de Buenos Aires, Patricias Argentinas 435, Buenos Aires, 1405, Argentina.
Development. 2005 Jun;132(11):2561-71. doi: 10.1242/dev.01839. Epub 2005 Apr 27.
Substrate-specific degradation of proteins by the ubiquitin-proteasome pathway is a precise mechanism that controls the abundance of key cell regulators. SCF complexes are a family of E3 ubiquitin ligases that target specific proteins for destruction at the 26S-proteasome. These complexes are composed of three constant polypeptides--Skp1, Cullin1/3 and Roc1/Rbx1--and a fourth variable adapter, the F-box protein. Slimb (Slmb) is a Drosophila F-Box protein that fulfills several roles in development and cell physiology. We analyzed its participation in egg chamber development and found that slmb is required in both the follicle cells and the germline at different stages of oogenesis. We observed that in slmb somatic clones, morphogenesis of the germarium and encapsulation of the cyst were altered, giving rise to egg chambers with extra germline cells and two oocytes. Furthermore, in slmb somatic clones, we observed ectopic Fasciclin 3 expression, suggesting a delay in follicle cell differentiation, which correlated with the occurrence of ectopic polar cells, lack of interfollicular stalks and mislocalization of the oocyte. Later in oogenesis, Slmb was required in somatic cells to specify the position, size and morphology of dorsal appendages. Mild overactivation of the Dpp pathway caused similar phenotypes that could be antagonized by simultaneous overexpression of Slmb, suggesting that Slmb might normally downregulate the Dpp pathway in follicle cells. Indeed, ectopic expression of a dad-LacZ enhancer trap revealed that the Dpp pathway was upregulated in slmb somatic clones and, consistent with this, ectopic accumulation of the co-Smad protein, Medea, was recorded. By analyzing slmb germline clones, we found that loss of Slmb provoked a reduction in E2f2 and Dp levels, which correlated with misregulation of mitotic cycles during cyst formation, abnormal nurse cell endoreplication and impairment of dumping of the nurse cell content into the oocyte.
泛素 - 蛋白酶体途径对蛋白质进行底物特异性降解是一种精确的机制，可控制关键细胞调节因子的丰度。SCF复合物是一类E3泛素连接酶，可靶向特定蛋白质在26S蛋白酶体处进行降解。这些复合物由三种恒定的多肽——Skp1、Cullin1/3和Roc1/Rbx1——以及第四种可变衔接子F - 盒蛋白组成。Slimb（Slmb）是一种果蝇F - 盒蛋白，在发育和细胞生理学中发挥多种作用。我们分析了它在卵室发育中的参与情况，发现slmb在卵子发生的不同阶段在卵泡细胞和生殖系中都是必需的。我们观察到，在slmb体细胞克隆中，生殖腺的形态发生和囊肿的包封发生了改变，产生了带有额外生殖系细胞和两个卵母细胞的卵室。此外，在slmb体细胞克隆中，我们观察到异位的Fasciclin 3表达，这表明卵泡细胞分化延迟，这与异位极细胞的出现、滤泡间柄的缺乏以及卵母细胞的定位错误相关。在卵子发生的后期，体细胞需要Slmb来确定背侧附属物的位置、大小和形态。Dpp途径的轻度过度激活会导致类似的表型，而同时过表达Slmb可以拮抗这些表型，这表明Slmb可能通常在卵泡细胞中下调Dpp途径。事实上，dad - LacZ增强子陷阱的异位表达表明，Dpp途径在slmb体细胞克隆中上调，与此一致的是，记录到了共Smad蛋白Medea的异位积累。通过分析slmb生殖系克隆，我们发现Slmb的缺失导致E2f2和Dp水平降低，并与囊肿形成过程中有丝分裂周期的失调、异常的滋养细胞内复制以及滋养细胞内容物向卵母细胞倾倒的受损相关。
