The arrest gene is required for germline cyst formation during Drosophila oogenesis

In Drosophila, oogenesis is initiated when a germline stem cell produces a differentiating daughter cell called the cystoblast. The cystoblast undergo es four rounds of synchronous divisions with incomplete cytokinesis to gene rate a syncytial cyst of 16 interconnected cystocytes, in which one cystocy te differentiates into an oocyte, Strong mutations of the arrest (aret) gen e disrupt cyst formation and cause the production of clusters of ill-differ entiated germline cells that retain cellular and molecular characteristics of cystoblasts. These mutant germ cells express high levels of BAM-C and SX L proteins in the cytoplasm but do not accumulate markers for advanced cyst ocytes or differentiating oocytes, such as the nuclear localization of SXL or the accumulation of osk mRNA, orb mRNA, and cytoplasmic dynein, However, the mutant germ cells do not contain spectrosomes, the cytoplasmic structu re that objectifies the divisional asymmetry of the cystoblast. The aret mu tant germ cells undergo active mitosis with complete cytokinesis, Their mit osis is accompanied by massive necrosis, so that the number of germ cells i n a stem cell-derived cluster ranges from one to greater than 70. These def ects of aret mutants reveal a novel function of aret as the first gene with a defined function in the cystoblast to cyst transition during early oogen esis. (C) 2001 Wiley-Liss, Inc.