Nyström Kristina, Abrantes Joana, Lopes Ana Margarida, Le Moullac-Vaidye Béatrice, Marchandeau Stéphane, Rocher Jézabel, Ruvoën-Clouet Nathalie, Esteves Pedro J, Le Pendu Jacques
INSERM, U892; CNRS, UMR6299; Nantes University, Nantes, France; Department of Infectious Diseases, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
INSERM, U892; CNRS, UMR6299; Nantes University, Nantes, France; CIBIO, InBIO-Research Network in Biodiversity and Evolutionary Biology, Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, Vairão, Portugal.
PLoS Pathog. 2015 Apr 15;11(4):e1004759. doi: 10.1371/journal.ppat.1004759. eCollection 2015 Apr.
RHDV (rabbit hemorrhagic disease virus), a virulent calicivirus, causes high mortalities in European rabbit populations (Oryctolagus cuniculus). It uses α1,2fucosylated glycans, histo-blood group antigens (HBGAs), as attachment factors, with their absence or low expression generating resistance to the disease. Synthesis of these glycans requires an α1,2fucosyltransferase. In mammals, there are three closely located α1,2fucosyltransferase genes rSec1, rFut2 and rFut1 that arose through two rounds of duplications. In most mammalian species, Sec1 has clearly become a pseudogene. Yet, in leporids, it does not suffer gross alterations, although we previously observed that rabbit Sec1 variants present either low or no activity. Still, a low activity rSec1 allele correlated with survival to an RHDV outbreak. We now confirm the association between the α1,2fucosyltransferase loci and survival. In addition, we show that rabbits express homogenous rFut1 and rFut2 levels in the small intestine. Comparison of rFut1 and rFut2 activity showed that type 2 A, B and H antigens recognized by RHDV strains were mainly synthesized by rFut1, and all rFut1 variants detected in wild animals were equally active. Interestingly, rSec1 RNA levels were highly variable between individuals and high expression was associated with low binding of RHDV strains to the mucosa. Co-transfection of rFut1 and rSec1 caused a decrease in rFut1-generated RHDV binding sites, indicating that in rabbits, the catalytically inactive rSec1 protein acts as a dominant-negative of rFut1. Consistent with neofunctionalization of Sec1 in leporids, gene conversion analysis showed extensive homogenization between Sec1 and Fut2 in leporids, at variance with its limited degree in other mammals. Gene conversion additionally involving Fut1 was also observed at the C-terminus. Thus, in leporids, unlike in most other mammals where it became extinct, Sec1 evolved a new function with a dominant-negative effect on rFut1, contributing to fucosylated glycan diversity, and allowing herd protection from pathogens such as RHDV.
兔出血症病毒（RHDV）是一种烈性杯状病毒，可导致欧洲兔种群（穴兔）的高死亡率。它利用α1,2岩藻糖基化聚糖，即组织血型抗原（HBGA）作为附着因子，缺乏或低表达这些聚糖会产生对该疾病的抗性。这些聚糖的合成需要一种α1,2岩藻糖基转移酶。在哺乳动物中，有三个紧密相邻的α1,2岩藻糖基转移酶基因rSec1、rFut2和rFut1，它们是通过两轮复制产生的。在大多数哺乳动物物种中，Sec1显然已成为假基因。然而，在兔科动物中，它没有发生重大改变，尽管我们之前观察到兔Sec1变体的活性很低或没有活性。尽管如此，一个低活性的rSec1等位基因与RHDV爆发后的存活相关。我们现在证实了α1,2岩藻糖基转移酶基因座与存活之间的关联。此外，我们表明兔子在小肠中表达均匀的rFut1和rFut2水平。rFut1和rFut2活性的比较表明，RHDV毒株识别的2型A、B和H抗原主要由rFut1合成，并且在野生动物中检测到的所有rFut1变体活性相同。有趣的是，rSec1 RNA水平在个体之间高度可变，高表达与RHDV毒株与黏膜的低结合相关。rFut1和rSec1的共转染导致rFut1产生的RHDV结合位点减少，这表明在兔子中，无催化活性的rSec1蛋白作为rFut1的显性负性蛋白发挥作用。与兔科动物中Sec1的新功能化一致，基因转换分析表明兔科动物中Sec1和Fut2之间存在广泛的同质化，这与其他哺乳动物中其有限的同质化程度不同。在C端还观察到另外涉及Fut1的基因转换。因此，在兔科动物中，与大多数其他已灭绝的哺乳动物不同，Sec1进化出了一种对rFut1具有显性负性作用的新功能，有助于岩藻糖基化聚糖的多样性，并使兔群免受RHDV等病原体的侵害。
