Institute of Genome Biology, Research Institute for Farm Animal Biology (FBN), Dummerstorf, Germany.
Institute of Nutritional Physiology, Research Institute for Farm Animal Biology (FBN), Dummerstorf, Germany.
Sci Rep. 2022 Aug 5;12(1):13469. doi: 10.1038/s41598-022-17798-5.
The insertion of an endogenous retroviral long terminal repeat (LTR) sequence into the bovine apolipoprotein B (APOB) gene is causal to the inherited genetic defect cholesterol deficiency (CD) observed in neonatal and young calves. Affected calves suffer from developmental abnormalities, symptoms of incurable diarrhoea and often die within weeks to a few months after birth. Neither the detailed effects of the LTR insertion on APOB expression profile nor the specific mode of inheritance nor detailed phenotypic consequences of the mutation are undisputed. In our study, we analysed German Holstein dairy heifers at the peak of hepatic metabolic load and exposed to an additional pathogen challenge for clinical, metabolic and hepatic transcriptome differences between wild type (CDF) and heterozygote carriers of the mutation (CDC). Our data revealed that a divergent allele-biased expression pattern of the APOB gene in heterozygous CDC animals leads to a tenfold higher expression of exons upstream and a decreased expression of exons downstream of the LTR insertion compared to expression levels of CDF animals. This expression pattern could be a result of enhancer activity induced by the LTR insertion, in addition to a previously reported artificial polyadenylation signal. Thus, our data support a regulatory potential of mobile element insertions. With regard to the phenotype generated by the LTR insertion, heterozygote CDC carriers display significantly differential hepatic expression of genes involved in cholesterol biosynthesis and lipid metabolism. Phenotypically, CDC carriers show a significantly affected lipomobilization compared to wild type animals. These results reject a completely recessive mode of inheritance for the CD defect, which should be considered for selection decisions in the affected population. Exemplarily, our results illustrate the regulatory impact of mobile element insertions not only on specific host target gene expression but also on global transcriptome profiles with subsequent biological, functional and phenotypic consequences in a natural in-vivo model of a non-model mammalian organism.
牛载脂蛋白 B（APOB）基因中内源性逆转录病毒长末端重复（LTR）序列的插入是导致新生和幼牛中观察到的遗传性胆固醇缺乏（CD）遗传缺陷的原因。受影响的小牛患有发育异常、无法治愈的腹泻症状，并且经常在出生后数周到数月内死亡。LTR 插入对 APOB 表达谱的详细影响、特定的遗传模式以及突变的详细表型后果均存在争议。在我们的研究中，我们分析了处于肝代谢负荷高峰期的德国荷斯坦奶牛小母牛，并在面临额外病原体挑战时，比较了野生型（CDF）和突变杂合子携带者（CDC）的临床、代谢和肝转录组差异。我们的数据表明，在杂合子 CDC 动物中，APOB 基因的等位基因偏倚表达模式导致 LTR 插入上游的外显子表达增加十倍，而 LTR 插入下游的外显子表达减少，与 CDF 动物的表达水平相比。这种表达模式可能是 LTR 插入诱导的增强子活性的结果，除了之前报道的人工聚腺苷酸化信号之外。因此，我们的数据支持移动元件插入的调节潜力。就 LTR 插入产生的表型而言，杂合子 CDC 携带者显示胆固醇生物合成和脂质代谢相关基因的肝表达存在显著差异。表型上，CDC 携带者的脂肪动员明显受到影响，与野生型动物相比。这些结果拒绝了 CD 缺陷的完全隐性遗传模式，这在受影响的人群中应考虑用于选择决策。例如，我们的结果说明了移动元件插入不仅对特定的宿主靶基因表达，而且对自然非模型哺乳动物体内模型中的全局转录组谱具有调节作用，随后具有生物学、功能和表型后果。
