Expansion of MHC-IIB Has Constrained the Evolution of MHC-IIA in Passerines
Ruesink-Bueno, Iris Liesbeth LU ; Drews, Anna LU ; O’Connor, Emily Amelia LU
and Westerdahl, Helena
LU
(2024)
In Genome Biology and Evolution
16(11).
- Abstract
The major histocompatibility complex (MHC) is central in adaptive immunity, with the highly polymorphic MHC genes encoding antigen-presenting molecules. Two MHC class II (MHC-II) loci, DA1 and DA2, predate the radiation of extant birds and persist throughout much of the avian phylogeny. Within each locus, the MHC-II molecules are encoded by A-genes (DAA) and B-genes (DAB), which are arranged in A–B dyads. However, in passerines (order Passeriformes), the DA2 locus has been lost, and the ancestral A–B dyad at the DA1 locus has been replaced by a putatively single A-gene (DAA1) and an array of highly polymorphic B-genes (DAB1). In this study, we genotyped the DAA1 gene of 15 passerine species and confirmed that passerines possess just one... (More)
The major histocompatibility complex (MHC) is central in adaptive immunity, with the highly polymorphic MHC genes encoding antigen-presenting molecules. Two MHC class II (MHC-II) loci, DA1 and DA2, predate the radiation of extant birds and persist throughout much of the avian phylogeny. Within each locus, the MHC-II molecules are encoded by A-genes (DAA) and B-genes (DAB), which are arranged in A–B dyads. However, in passerines (order Passeriformes), the DA2 locus has been lost, and the ancestral A–B dyad at the DA1 locus has been replaced by a putatively single A-gene (DAA1) and an array of highly polymorphic B-genes (DAB1). In this study, we genotyped the DAA1 gene of 15 passerine species and confirmed that passerines possess just one copy of DAA1. We then compared selection patterns in DAA1 between passerines and nonpasserines and found that exon 2, which encodes the antigen-presenting domain, has been subject to weaker positive selection and stronger negative selection in passerines compared with nonpasserines. Additional comparisons showed that the patterns of selection in the passerine DAA1 gene are unlikely to be related to the loss of the DA2 locus. Instead, our findings suggest that the expansion of DAB1 (MHC-IIB) has imposed an evolutionary constraint on the passerine DAA1 (MHC-IIA) gene. We speculate that this constraint may be the result of each DAA1 chain forming heterodimers with many different DAB1 chains.
(Less)
- author
- Ruesink-Bueno, Iris Liesbeth
LU
; Drews, Anna
LU
; O’Connor, Emily Amelia
LU
and Westerdahl, Helena
LU
- organization
- publishing date
- 2024-11-01
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- macroevolution, major histocompatibility complex (MHC), MHC-IIA, negative selection, Passeriformes, positive selection
- in
- Genome Biology and Evolution
- volume
- 16
- issue
- 11
- article number
- evae236
- publisher
- Oxford University Press
- external identifiers
-
- pmid:39462092
- scopus:85209479318
- ISSN
- 1759-6653
- DOI
- 10.1093/gbe/evae236
- language
- English
- LU publication?
- yes
- additional info
- Publisher Copyright: © The Author(s) 2024.
- id
- ef119733-0248-4d2d-9291-bc92510c3f45
- date added to LUP
- 2025-01-13 17:18:28
- date last changed
- 2025-07-01 07:18:40
@article{ef119733-0248-4d2d-9291-bc92510c3f45,
abstract = {{<p>The major histocompatibility complex (MHC) is central in adaptive immunity, with the highly polymorphic MHC genes encoding antigen-presenting molecules. Two MHC class II (MHC-II) loci, DA1 and DA2, predate the radiation of extant birds and persist throughout much of the avian phylogeny. Within each locus, the MHC-II molecules are encoded by A-genes (DAA) and B-genes (DAB), which are arranged in A–B dyads. However, in passerines (order Passeriformes), the DA2 locus has been lost, and the ancestral A–B dyad at the DA1 locus has been replaced by a putatively single A-gene (DAA1) and an array of highly polymorphic B-genes (DAB1). In this study, we genotyped the DAA1 gene of 15 passerine species and confirmed that passerines possess just one copy of DAA1. We then compared selection patterns in DAA1 between passerines and nonpasserines and found that exon 2, which encodes the antigen-presenting domain, has been subject to weaker positive selection and stronger negative selection in passerines compared with nonpasserines. Additional comparisons showed that the patterns of selection in the passerine DAA1 gene are unlikely to be related to the loss of the DA2 locus. Instead, our findings suggest that the expansion of DAB1 (MHC-IIB) has imposed an evolutionary constraint on the passerine DAA1 (MHC-IIA) gene. We speculate that this constraint may be the result of each DAA1 chain forming heterodimers with many different DAB1 chains.</p>}},
author = {{Ruesink-Bueno, Iris Liesbeth and Drews, Anna and O’Connor, Emily Amelia and Westerdahl, Helena}},
issn = {{1759-6653}},
keywords = {{macroevolution; major histocompatibility complex (MHC); MHC-IIA; negative selection; Passeriformes; positive selection}},
language = {{eng}},
month = {{11}},
number = {{11}},
publisher = {{Oxford University Press}},
series = {{Genome Biology and Evolution}},
title = {{Expansion of MHC-IIB Has Constrained the Evolution of MHC-IIA in Passerines}},
url = {{http://dx.doi.org/10.1093/gbe/evae236}},
doi = {{10.1093/gbe/evae236}},
volume = {{16}},
year = {{2024}},
}