Ovine HSP90AA1 Expression Rate Is Affected by Several SNPs at the Promoter under Both Basal and Heat Stress Conditions

The aim of this work was to investigate the association between polymorphisms located at the HSP90AA1 ovine gene promoter and gene expression rate under different environmental conditions, using a mixed model approach. Blood samples from 120 unrelated rams of the Manchega sheep breed were collected at three time points differing in environmental conditions. Rams were selected on the basis of their genotype for the transversion G/C located 660 base pairs upstream the gene transcription initiation site. Animals were also genotyped for another set of 6 SNPs located at the gene promoter. Two SNPs, G/C−660 and A/G−444, were associated with gene overexpression resulting from heat stress. The composed genotype CC−660-AG−444 was the genotype having the highest expression rates with fold changes ranging from 2.2 to 3.0. The genotype AG−522 showed the highest expression levels under control conditions with a fold change of 1.4. Under these conditions, the composed genotype CC−601-TT−524-AG−522-TT−468 is expected to be correlated with higher basal expression of the gene according to genotype frequencies and linkage disequilibrium values. Some putative transcription factors were predicted for binding sites where the SNPs considered are located. Since the expression rate of the gene under alternative environmental conditions seems to depend on the composed genotype of several SNPs located at its promoter, a cooperative regulation of the transcription of the HSP90AA1 gene could be hypothesized. Nevertheless epigenetic regulation mechanisms cannot be discarded.本研究旨在通过混合模型方法，探究绵羊热休克蛋白90α1（HSP90AA1）基因启动子区域的多态性与不同环境条件下该基因的表达水平之间的关联。研究共采集120只无亲缘关系的曼彻格绵羊公羊的血液样本，采样时点共3个，各时点的环境条件存在差异。研究对象根据该基因转录起始位点上游660个碱基对处的G/C颠换基因型进行筛选，同时对该基因启动子区域内的另外6个单核苷酸多态性（Single Nucleotide Polymorphism, SNP）位点进行基因分型。结果显示，G/C−660与A/G−444这两个SNP位点与热应激诱导的基因过表达显著相关。其中组合基因型CC−660-AG−444的基因表达水平最高，其表达倍数变化范围为2.2至3.0。在对照条件下，基因型AG−522的基因表达水平最高，对应表达倍数变化为1.4。基于基因型频率与连锁不平衡（Linkage Disequilibrium, LD）值分析，在对照条件下，组合基因型CC−601-TT−524-AG−522-TT−468有望与该基因更高的基础表达水平相关联。研究人员针对上述SNP位点所在的结合区域预测了若干潜在转录因子。鉴于该基因在不同环境条件下的表达水平似乎取决于其启动子区域内多个SNP的组合基因型，因此可推测绵羊HSP90AA1基因的转录存在协同调控机制，但表观遗传调控机制仍不能被排除。