Marchal J A, Acosta M J, Bullejos M, Puerma E, Díaz de la Guardia R, Sánchez A
Departamento de Biología Experimental, Facultad de Ciencias Experimentales, Universidad de Jaén, Campus Las Lagunillas s/n, E-23071, Jaén, Spain.
Chromosome Res. 2006;14(2):177-86. doi: 10.1007/s10577-006-1034-9. Epub 2006 Mar 17.
Long interspersed nuclear elements (L1 or LINE-1) are the most abundant and active retroposons in the mammalian genome. Traditionally, the bulk of L1 sequences have been explained by the 'selfish DNA' hypothesis; however, recently it has been also argued that L1s could play an important role in genome and gene organizations. The non-random chromosomal distribution of these retroelements is a striking feature considered to reflect this functionality. In the present study we have cloned and analyzed three different L1 fragments from the genome of the rodent Microtus cabrerae. In addition, we have examined the chromosomal distribution of this L1 in several species of Microtus, a very interesting group owing to the presence in some species of enlarged ('giant') sex chromosomes. Interestingly, in all species analyzed, L1-retroposons have preferentially accumulated on both the giant- and the normal-sized sex chromosomes compared with the autosomes. Also we have demonstrated that L1-retroposons are not similarly distributed among the heterochromatic blocks of the giant sex chromosomes in M. cabrerae and M. agrestis, which suggest that L1 retroposition and amplification over the sex heterochromatin have been different and independent processes in each species. Finally, we proposed that the main factors responsible for the L1 distribution on the mammalian sex chromosomes are the heterochromatic nature of the Y chromosome and the possible role of L1 sequences during the X-inactivation process.
长散在核元件（L1或LINE-1）是哺乳动物基因组中数量最多且最活跃的反转录转座子。传统上，大部分L1序列是根据“自私DNA”假说进行解释的；然而，最近也有人认为L1可能在基因组和基因组织中发挥重要作用。这些反转录元件在染色体上的非随机分布是一个显著特征，被认为反映了这种功能。在本研究中，我们从啮齿动物卡氏田鼠的基因组中克隆并分析了三个不同的L1片段。此外，我们还研究了这种L1在几种田鼠中的染色体分布，田鼠是一个非常有趣的群体，因为在一些物种中存在增大的（“巨型”）性染色体。有趣的是，在所有分析的物种中，与常染色体相比，L1反转录转座子优先在巨型和正常大小的性染色体上积累。我们还证明，L1反转录转座子在卡氏田鼠和田野鼠的巨型性染色体的异染色质区域中的分布并不相似，这表明L1在每个物种的性异染色质上的反转录和扩增是不同且独立的过程。最后，我们提出，哺乳动物性染色体上L1分布的主要因素是Y染色体的异染色质性质以及L1序列在X染色体失活过程中可能发挥的作用。
