Pandey Shova, Nguyen An Tri, Maricle Audrey K, DiMario Patrick J
Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
Int J Mol Sci. 2025 Jun 7;26(12):5480. doi: 10.3390/ijms26125480.
retrotransposons reside exclusively within the regions of 10-20% of all rDNA genes comprising the nucleolar organizer loci on the X and Y chromosomes of . These -inserted genes are normally silent and heterochromatic. When expressed, however, the transcript is co-transcribed with the rRNA. Self-cleavage releases a 3.6 kb mature transcript that encodes a single protein with endonuclease and reverse transcriptase activities that facilitate element transposition by target-primed reverse transcription. While we know the molecular details of transposition, we know little about the genetic mechanisms that initiate transcription. Here, we examine expression in wild type versus mutant backgrounds. expression in stage 1-4 wild type egg chambers was variable depending on the stock. expression was silent in wild type stages 5-10 but was consistently active during nurse cell nuclear breakdown in stages 12-13 regardless of the genetic background. Massive expression occurred in stages 5-10 upon loss of Udd, an RNA Pol I transcription factor. Similarly, loss of Nopp140, an early ribosome assembly factor, induced expression more so in somatic tissues. Interestingly, over-expression of the Nopp140-RGG isoform but not the Nopp140-True isoform induced expression in larval somatic tissues, suggesting Nopp140-RGG could potentially affect rDNA chromatin structure. Conversely, mutations in genes encoding ribosomal proteins had minor positive effects on expression. We conclude that expression is largely controlled by factors regulating RNA Pol I transcription and early ribosome assembly.
逆转座子仅存在于所有rDNA基因中10 - 20%的区域内，这些区域构成了[物种名称]X和Y染色体上的核仁组织区位点。这些插入的基因通常是沉默且异染色质化的。然而，当它们表达时，[逆转座子名称]转录本会与rRNA一起被共转录。自我切割释放出一个3.6 kb的成熟[逆转座子名称]转录本，该转录本编码一种具有内切核酸酶和逆转录酶活性的单一蛋白质，通过靶标引发的逆转录促进[逆转座子名称]元件的转座。虽然我们了解[逆转座子名称]转座的分子细节，但对于启动[逆转座子名称]转录的遗传机制却知之甚少。在这里，我们研究了野生型与突变背景下[逆转座子名称]的表达情况。在1 - 4期野生型卵室中，[逆转座子名称]的表达因品系而异。在野生型5 - 10期，[逆转座子名称]表达沉默，但在12 - 13期的滋养细胞核解体过程中始终活跃，无论遗传背景如何。在RNA聚合酶I转录因子Udd缺失时，5 - 10期会出现大量[逆转座子名称]表达。同样，早期核糖体组装因子Nopp140的缺失在体细胞组织中更易诱导[逆转座子名称]表达。有趣的是，Nopp140 - RGG异构体而非Nopp140 - True异构体的过表达在幼虫体细胞组织中诱导了[逆转座子名称]表达，这表明Nopp140 - RGG可能潜在地影响rDNA染色质结构。相反，编码核糖体蛋白的基因突变对[逆转座子名称]表达有轻微的正向影响。我们得出结论，[逆转座子名称]的表达在很大程度上受调节RNA聚合酶I转录和早期核糖体组装的因子控制。
