Instituto de Investigação e Inovação em Saúde, Universidade do Porto (I3S), Porto, Portugal Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP), Porto, Portugal Department of Biochemistry and Molecular Biology-IUOPA, University of Oviedo, Oviedo, Spain Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto, Porto, Portugal.
Instituto de Investigação e Inovação em Saúde, Universidade do Porto (I3S), Porto, Portugal Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP), Porto, Portugal.
Mol Biol Evol. 2016 Jan;33(1):93-108. doi: 10.1093/molbev/msv199. Epub 2015 Sep 29.
The human kallikrein (KLK) cluster, located at chromosome 19q13.3-13.4, encodes 15 serine proteases, including neighboring genes (KLK3, KLK2, KLK4, and KLK5) with key roles in the cascades of semen liquefaction, tooth enamel maturation, and skin desquamation. KLK2 and KLK3 were previously identified as targets of adaptive evolution in primates through different mechanisms linked to reproductive biology and, in humans, genome-wide scans of positive selection captured, a yet unexplored, evidence for KLK neutrality departure in East Asians. We perform a detailed evaluation of KLK3-KLK5 variability in the 1000 Genomes samples from East Asia, Europe, and Africa, which was sustained by our own sequencing. In East Asians, we singled out a 70-kb region surrounding KLK4 that combined unusual low levels of diversity, high frequency variants with significant levels of population differentiation (FST > 0.5) and fairly homogenous haplotypes given the large local recombination rates. Among these variants, rs1654556_G, rs198968_T, and rs17800874_A stand out for their location on putative regulatory regions and predicted functional effects, namely the introduction of several microRNA binding sites and a repressor motif. Our functional assays carried out in different cellular models showed that rs198968_T and rs17800874_A operate synergistically to reduce KLK4 expression and could be further assisted by rs1654556_G. Considering the previous findings that KLK4 inactivation causes enamel malformations in humans and mice, and that this gene is coexpressed in epidermal layers along with several substrates involved in either cell adhesion or keratinocyte differentiation, we propose KLK4 as another target of selection in East Asians correlated to tooth and epidermal morphological traits.
人类激肽释放酶（KLK）簇位于 19q13.3-13.4 染色体上，编码 15 种丝氨酸蛋白酶，包括邻近基因（KLK3、KLK2、KLK4 和 KLK5），它们在精液液化、牙釉质成熟和皮肤脱屑的级联反应中起着关键作用。KLK2 和 KLK3 先前通过与生殖生物学相关的不同机制被确定为灵长类动物适应进化的靶点，而在人类中，对正选择的全基因组扫描捕获了东亚人群 KLK 中性偏离的未被探索的证据。我们对东亚、欧洲和非洲的 1000 基因组样本中的 KLK3-KLK5 变异性进行了详细评估，这些样本由我们自己的测序提供支持。在东亚人群中，我们在 KLK4 周围鉴定出一个 70kb 的区域，该区域结合了不同寻常的低多样性、高频率变异体和具有显著群体分化（FST>0.5）的高频率变异体，以及考虑到较大的局部重组率，相当同质的单倍型。在这些变体中，rs1654556_G、rs198968_T 和 rs17800874_A 因其位于假定的调控区域和预测的功能效应而引人注目，即引入了几个 microRNA 结合位点和一个抑制子基序。我们在不同的细胞模型中进行的功能检测表明，rs198968_T 和 rs17800874_A 协同作用降低 KLK4 的表达，并且可能进一步受到 rs1654556_G 的辅助。考虑到先前的发现，KLK4 的失活会导致人类和小鼠的牙釉质畸形，并且该基因与参与细胞黏附或角质形成细胞分化的几个底物一起在表皮层中共同表达，我们提出 KLK4 是与牙齿和表皮形态特征相关的东亚人群选择的另一个靶点。
