Mével-Ninio M, Terracol R, Kafatos F C
Centre de Génétique Moléculaire du CNRS, Gif sur Yvette, France.
EMBO J. 1991 Aug;10(8):2259-66. doi: 10.1002/j.1460-2075.1991.tb07762.x.
As defined by dominant and recessive ovo mutations, the ovo gene is required for development of the Drosophila female germ line, and does not exert any function in males or in somatic tissues. However, reversion of dominant ovo mutations can result in new phenotypes that are not related to the female germ line: the svb and lzl mutations affect cuticle and eye development, respectively. We have identified a 7.2 kb genomic fragment that rescues ovo mutations in transgenic Drosophila and thus contains all sequences necessary for ovo+ function. This fragment has been sequenced almost in its entirety, defining the ovo locus at the molecular level. Multiple copies of the same fragment also rescue the lzl mutation. They do not rescue svb mutations, in agreement with genetic evidence that the svb function requires additional, more distal sequences. Nevertheless, a number of transposable element insertions that induce a svb phenotype interrupt the coding sequence of ovo. Taken together, the genetic and molecular data indicate the existence of a complex locus, where the ovo and svb functions depend on overlapping coding sequences but distinct regulatory elements. The data also suggest a model for the lzl phenotype. Expression of ovo at the RNA level is detectable at stage 8 of oogenesis in nurse cells and persists through the rest of oogenesis and in early embryogenesis. The ovo transcript encodes a protein of at least 1209 amino acids with four zinc fingers, suggesting that ovo might be a transcription factor required for female germ line maintenance and gametogenesis.
根据显性和隐性卵突变的定义，卵基因是果蝇雌性生殖系发育所必需的，在雄性或体细胞组织中不发挥任何功能。然而，显性卵突变的回复突变可导致与雌性生殖系无关的新表型：svb和lzl突变分别影响表皮和眼睛发育。我们鉴定出一个7.2 kb的基因组片段，它能挽救转基因果蝇中的卵突变，因此包含卵+功能所需的所有序列。该片段几乎已全部测序，在分子水平上定义了卵基因座。同一片段的多个拷贝也能挽救lzl突变。它们不能挽救svb突变，这与遗传证据一致，即svb功能需要额外的、更远端的序列。然而，一些诱导svb表型的转座元件插入中断了卵的编码序列。综合来看，遗传和分子数据表明存在一个复杂的基因座，其中卵和svb功能依赖于重叠的编码序列但不同的调控元件。这些数据还提出了一个关于lzl表型的模型。在卵子发生的第8阶段，在滋养细胞中可检测到卵基因在RNA水平的表达，并在卵子发生的其余阶段以及早期胚胎发生中持续存在。卵转录本编码一种至少含有1209个氨基酸且有四个锌指的蛋白质，这表明卵可能是雌性生殖系维持和配子发生所需的转录因子。
