Lisachov Artem, Andreyushkova Daria, Davletshina Guzel, Prokopov Dmitry, Romanenko Svetlana, Galkina Svetlana, Saifitdinova Alsu, Simonov Evgeniy, Borodin Pavel, Trifonov Vladimir
Institute of Environmental and Agricultural Biology (X-BIO), University of Tyumen, Lenina str. 23, 625003 Tyumen, Russia.
Institute of Cytology and Genetics SB RAS, Acad. Lavrentiev Ave. 10, 630090 Novosibirsk, Russia.
Genes (Basel). 2021 May 20;12(5):779. doi: 10.3390/genes12050779.
Heteromorphic W and Y sex chromosomes often experience gene loss and heterochromatinization, which is frequently viewed as their "degeneration". However, the evolutionary trajectories of the heterochromosomes are in fact more complex since they may not only lose but also acquire new sequences. Previously, we found that the heterochromatic W chromosome of a lizard (Lacertidae) is decondensed and thus transcriptionally active during the lampbrush stage. To determine possible sources of this transcription, we sequenced DNA from a microdissected W chromosome sample and a total female DNA sample and analyzed the results of reference-based and de novo assembly. We found a new repetitive sequence, consisting of fragments of an autosomal protein-coding gene ATF7IP2, several SINE elements, and sequences of unknown origin. This repetitive element is distributed across the whole length of the W chromosome, except the centromeric region. Since it retained only 3 out of 10 original ATF7IP2 exons, it remains unclear whether it is able to produce a protein product. Subsequent studies are required to test the presence of this element in other species of Lacertidae and possible functionality. Our results provide further evidence for the view of W and Y chromosomes as not just "degraded" copies of Z and X chromosomes but independent genomic segments in which novel genetic elements may arise.
异形的W和Y性染色体常经历基因丢失和异染色质化，这通常被视为它们的“退化”。然而，异染色体的进化轨迹实际上更为复杂，因为它们不仅可能丢失基因，还可能获得新序列。此前，我们发现一种蜥蜴（蜥蜴科）的异染色质W染色体在灯刷期会解聚，因此具有转录活性。为了确定这种转录的可能来源，我们对从显微切割的W染色体样本和雌性全基因组DNA样本中提取的DNA进行了测序，并分析了基于参考序列组装和从头组装的结果。我们发现了一种新的重复序列，它由常染色体蛋白质编码基因ATF7IP2的片段、几个短散在核元件（SINE）以及来源不明的序列组成。这种重复元件分布在W染色体的全长上，除了着丝粒区域。由于它在10个原始的ATF7IP2外显子中只保留了3个，所以尚不清楚它是否能够产生蛋白质产物。后续研究需要测试这种元件在其他蜥蜴科物种中的存在情况以及可能的功能。我们的结果为以下观点提供了进一步的证据：W和Y染色体不仅仅是Z和X染色体的“退化”副本，而是独立的基因组片段，其中可能会出现新的遗传元件。
