Regulation of a Bovine Nonclassical Major Histocompatibility Complex Class I Gene Promoter1

Abstract

Studies have shown in humans and other species that the major histocompatibility complex class I (MHC-I) region is involved at a number of levels in the establishment and maintenance of pregnancy. The aim of this study was to characterize how a bovine nonclassical MHC-I gene (NC1) is regulated. Initial serial deletion experiments of a 2-kb fragment of the NC1 promoter identified regions with positive regulatory elements in the proximal promoter and evidence for a silencer module(s) further upstream that cooperatively contributed to constitutive NC1 expression. The cytokines interferon tau (IFNT), interferon gamma (IFNG), and interleukin 4 (IL4) significantly increased luciferase expression in NC1 promoter reporter constructs and endogenous NC1 mRNA levels in a bovine endometrial cell line. In addition, IFNG, IL3, IL4, and progesterone significantly increased Day 7 bovine blastocyst NC1 mRNA expression when supplemented during in vitro embryo culture. Site-directed mutagenesis analysis identified a STAT6 binding site that conferred IL4 responsiveness in the NC1 proximal promoter. Furthermore, methylation treatment of the proximal promoter, which contains a CpG island, completely abrogated constitutive NC1 expression. Overall, the findings presented here suggest that constitutive NC1 expression is regulated positively by elements in the proximal promoter, which are further controlled by upstream silencer modules. The promoter is responsive to IFNT, IFNG, and IL4, suggesting possible roles for these cytokines in bovine preimplantation embryo survival and/or maternal-fetal tolerance. Our studies also suggest that methylation of the proximal promoter, in particular, could play a significant role in regulating NC1 expression.

Characterization of the Th Profile of the Bovine Endometrium during the Oestrous Cycle and Early Pregnancy

“…Studies in cattle have identified enhanced expression of classical MHC-I transcripts in endometrial tissue [6,19-21] from Day 18 of pregnancy, while non-classical MHC-I transcripts have been detected in early cleavage stage bovine embryos [22] and in first and second trimester and term trophoblast tissues [23-25]. Furthermore, studies in our laboratory indicate that the expression of MHC class I mRNA by bovine embryos is both transcript- and embryo stage-specific [22] and can be regulated by a number of cytokines including IFNG, IL-4 and LIF [26,27]. Thus, although there is considerably less information relating to the mechanisms modulating the maternal immune response to the semi-allogenic conceptus in cattle, and although implantation and placentation in cattle is quite superficial in contrast to the invasive nature of these events in human, the large body of descriptive data from studies in bovine indicate that the maternal immune response is regulated during early pregnancy in this species.…”

Modulation of Maternal Immune System During Pregnancy in the Cow

“…2004). Additionally, the treatment of in vitro produced embryos with IL4, IL3, IFNG and progesterone increased the expression of NC1 (O’Gorman et al. 2010).…”

Major Histocompatibility Complex I Mediates Immunological Tolerance of the Trophoblast during Pregnancy and May Mediate Rejection during Parturition

“…Unlike in humans, classical BoLA with paternal antigens are known to be expressed during physiological pregnancy, in addition to nonclassical BoLA with “zero” antigens [36–38]. Throughout all of pregnancy, the paternal antigens are expressed on binuclear cells, which have a role in supporting pregnancy.…”