biostudies-literatureUnknown11Bjornestad SAUniversitetet i OsloMajor histocompatibility complex (MHC) class I and II are crucial for the adaptive immune system because they are involved in peptide presentation to T cells. Until recently, it was believed that MHC genes and their associated immune components had been conserved since their evolutionary emergence in jawed fish. However, sequencing of the Atlantic cod (<i>Gadus morhua</i>) genome revealed a loss of MHC class II genes, and an extreme expansion of MHC class I genes. These findings lead to the hypothesis that a loss of the MHC class II pathway coincided with a more versatile use of MHC class I, but so far there is no direct experimental evidence in support of this. To gain a deeper understanding of the function of the expanded MHC class I, we selected five MHC class I gene variants representiFrontiers in cell and developmental biology1050323https://www.ebi.ac.uk/biostudies/studies/S-EPMC9905690biostudies-literatureAtlantic cod (<i>Gadus morhua</i>) MHC I localizes to endolysosomal compartments independently of cytosolic sorting signals.PMC9905690Bakke OJentoft SSolbakken MHProgida CJakobsen KSBjornestad SAfalseAtlantic cod (<i>Gadus morhua</i>) MHC I localizes to endolysosomal compartments independently of cytosolic sorting signals.Major histocompatibility complex (MHC) class I and II are crucial for the adaptive immune system because they are involved in peptide presentation to T cells. Until recently, it was believed that MHC genes and their associated immune components had been conserved since their evolutionary emergence in jawed fish. However, sequencing of the Atlantic cod (<i>Gadus morhua</i>) genome revealed a loss of MHC class II genes, and an extreme expansion of MHC class I genes. These findings lead to the hypothesis that a loss of the MHC class II pathway coincided with a more versatile use of MHC class I, but so far there is no direct experimental evidence in support of this. To gain a deeper understanding of the function of the expanded MHC class I, we selected five MHC class I gene variants representi2023-01-01T00:00:00Z20232026-05-28T11:51:43.156Z2025-04-07T03:20:06.484ZS-EPMC99056903676036110.3389/fcell.2023.1050323