Molecular Genetics of the Drosophila Triplo-lethal Locus

基因剂量的改变往往对生物体的发育和/或生存有深远的影响，但对基因剂量效应的分子基础却知之甚少。果蝇三重致死基因(TPL)是理解基因剂量效应的一个独特而有趣的模型。TPL是已知的唯一一个当存在两个拷贝以外的任何拷贝时都是致命的遗传基因座。携带零、一、三或四个TPL拷贝的二倍体动物会死于晚期胚胎或早期一龄幼虫。第三方物流也可能有一种不寻常的遗传结构。虽然TPL的复制和缺陷很容易分离，但从未发现消除TPL功能的点突变，这表明TPL可能由冗余信息组成，或者它可能编码非翻译的RNA分子。最近的数据表明，TPL功能所必需的DNA已经被克隆。这一区域将通过标准的分子技术进行分析，包括克隆和测序以确定转录单位。候选基因将用于果蝇的转化实验，以鉴定TPL。在不久的将来，伯克利果蝇基因组计划将对这一基因组的这一区域进行测序，这将极大地帮助分析这一新的遗传位点。还将对TPL基因的抑制子SU(TPL)进行克隆和测序。SU(TPL)突变胚胎即使有三种剂量的TPL仍能存活，这表明这两个基因是相互作用的。目前已获得SU(TPL)的基因组克隆，并将对克隆进行分离和分析。了解SU(TPL)将使我们更好地理解为什么TPL如此剂量敏感以及导致癫痫的基础。TPL有两个使其新颖的特征。其一是其极高的剂量敏感性。另一个是它对突变的抵抗力，这表明了一种不同寻常的结构。这两种基因都使它的研究特别具有挑战性，但这样的基因在细胞中可能并不罕见。可能只是它们不容易被发现。非蛋白质编码基因也不容易通过DNA序列分析来识别。了解TPL可能会导致更多这类基因的发现，并进一步了解基因剂量的重要性。

Christensen9808209Alterations in gene dosage often have profound effects on the development and/or viability of organisms, yet little is known about the molecular basis of gene dosage effects. The Triplo-lethal locus of Drosophila (Tpl) is a unique and interesting model for understanding gene dosage effects. Tpl is the only genetic locus known that is lethal when present in anything other than two copies. Diploid animals with either zero, one, three or four copies of Tpl die as late embryos or early first-instar larvae. Tpl may also have an unusual genetic structure. While duplications and deficiencies of Tpl are readily isolated, point mutations that eliminate Tpl's function have never been found, suggesting that Tpl may consist of redundant information or it may code for a non-translated RNA molecule. Recent data suggest that the DNA that is necessary for Tpl function has been cloned. This region will be analyzed by standard molecular techniques, including cDNA cloning and sequencing to identify transcription units. Candidate genes will be used in Drosophila transformation experiments to identify Tpl. This region of the genome will be sequenced in the near future by the Berkeley Drosophila Genome Project, which will greatly aid the analysis of this novel genetic locus. Cloning and sequencing the Suppressor-of Tpl locus, Su(Tpl), will also be done. Su(Tpl) mutant embryos survive in spite of having three doses of Tpl, which shows an interaction of these two genes. Genomic clones of Su(Tpl) have already been obtained and cDNA clones will be isolated and analyzed. Understanding Su(Tpl) will lead to greater understanding of why Tpl is so dosage sensitive and the basis for the lethality.Tpl has two features that make it novel. One is its extreme dosage sensitivity. The other is its resistance to mutagenesis, suggesting an unusual structure. Both make its study especially challenging, but such genes may not be rare in the cell. It may only be that they are not easily discovered. Non-protein-coding genes will also not easily be identified via DNA sequence analysis. Understanding Tpl may lead to the discovery of many more genes of this type, and a further understanding of the importance of gene dosage.