RNA-seq Reveals Transcriptomic Shock Involving Transposable Elements Reactivation in Hybrids of Young Lake Whitefish Species
RNA-seq Reveals Transcriptomic Shock Involving Transposable Elements Reactivation in Hybrids of Young Lake Whitefish Species
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DOI：
10.1093/molbev/msu069
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发表时间：
2014-05-01
影响因子：
10.7
通讯作者：
Bernatchez, Louis
中科院分区：
文献类型：
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作者：
Dion-Cote, Anne-Marie;Renaut, Sebastien;Bernatchez, Louis
确定不同谱系间生殖隔离的分子基础是理解自然种群物种形成的重要一步。合子后屏障可导致杂交破裂，这是一种已在几个系统中记录的综合征，可能涉及转座因子的再激活。在北美东北部，两种湖泊白鱼谱系在类似于1.2万年前的冰川后湖泊中反复定居，一种矮沼泽物种从正常的底栖物种进化了多次。它们之间的生殖隔离是不完全的；在实验室中可以产生有活力的杂交种，但在回交胚胎中发生明显的死亡率，并与畸形表型有关，从而揭示了杂交破裂综合征。通过RNA-seq分析，本研究的目的是确定哪些基因在杂交中被错误调控，并严格检验转座因子再激活的假设。我们比较了纯胚、f1杂交种、健康回交和畸形回交在胚胎后期的转录组景观。在纯正常胚胎和矮胚之间首次发现了广泛的表达差异，与先前记录的适应性差异一致。在畸形回交中观察到明显的转录组范围内的放松，在所有比较中，超过15%的转录本差异表达，而纯亲本形式的差异表达为1.5%。有说服力的证据表明，转座因子和非编码转录物在畸形回交中重新激活。我们提出，杂交分解可能是由于广泛的基因组不相容，似乎包括转座因子。结合以往的研究，这些结果揭示了许多生殖障碍之间的协同作用，从而保持了这两个幼白鱼物种之间的差异。
Identifying the molecular basis of reproductive isolation among diverging lineages represents an essential step toward understanding speciation in natural populations. Postzygotic barriers can lead to hybrid breakdown, a syndrome that has been documented in several systems, potentially involving the reactivation of transposable elements. In northeastern North America, two lake whitefish lineages have repeatedly colonized postglacial lakes similar to 12,000 years ago, and a dwarf limnetic species has evolved multiple times from the normal benthic species. Reproductive isolation is incomplete between them; viable hybrids can be generated in the laboratory but significant mortality occurs and is associated with a malformed phenotype in backcross embryos, thus revealing a hybrid breakdown syndrome. By means of RNA-seq analyses, the objective of this study was to determine which genes were misregulated in hybrids and rigorously test the hypothesis of transposable element reactivation. We compared the transcriptomic landscape in pure embryos, F1-hybrids, and healthy and malformed backcrosses at the late embryonic stage. Extensive expression differences consistent with previously documented adaptive divergence between pure normal and dwarf embryos were identified for the first time. Pronounced transcriptome-wide deregulation in malformed backcrosses was observed, with over 15% of transcripts differentially expressed in all comparisons, compared with 1.5% between pure parental forms. Convincing evidence of transposable elements and noncoding transcripts reactivation in malformed backcrosses is presented. We propose that hybrid breakdown likely results from extensive genomic incompatibilities, plausibly encompassing transposable elements. Combined with previous studies, these results reveal synergy among many reproductive barriers, thus maintaining divergence between these two young whitefish species.