Muhammad Usman Ghani1, Shakeel
Hussain2, Anboyang3, Yan Chun
Xu4 and Dr Li Bo5*
1College of Wildlife Resources and Protected Area,
Northeast Forestry University, Harbin 150040, China;
drblouch18@gmail.com
2College of Wildlife Resources and Protected Area,
Northeast Forestry University, Harbin 150040, China;
shakil-alhusaini@hotmail.com
3Department of stem cell biology and medicine,
Graduate school of medical science, Kyushu University, Fukuoka 810-0000,
Japan; anboyang@med.kyushu-u.ac.jp
4State Forestry and Grassland Administration Research
Center of Engineering Technology for Wildlife; College of Wildlife
Resources and Protected Area, Harbin 150040, China; xu_danial@163.com
5College of Wildlife Resources and Protected Area,
Northeast Forestry University, Harbin 150040, China;
LIBO_770206@126.com
*Correspondence:
drblouch18@gmail.com;Tel:(+92-333-602-2399),
LIBO_770206@126.com; Tel: (+86-180-451-60508).
Abstract: In vertebrate animals, the molecules encoded by major
histocompatibility complex (MHC) genes play an essential role in the
adaptive immunity. MHC class I deal with intracellular pathogens (Virus)
in birds. MHC class I diversity depends on the consequence of local and
global environment selective pressure and gene flow. Here, we evaluated
the MHC class I gene in four species of Turdidae family from a
broad geographical area of northeast China. We isolated 77 MHC class I
sequence, including 47 putatively functional sequences and 30 pseudo
sequences from 80 individuals. Method based on analysis of cloned
amplicons (n=25 ) for each species, we found two and seven MHC I
sequence per individual indicates more than one MHC I loci identified in
all sampled species. Results revealed an overall elevated genetic
diversity at MHC class I, evidence of different selection patterns among
the domains of PBR and non-PBR. Alleles found to be divergent with
overall polymorphic sites per species ranging between 58 to 70 (out of
291 sites). Moreover, trans-species alleles were evident due to
convergent evolution or recent speciation for the genus. Phylogenetic
relationships among MHC I show an intermingling of alleles clustering
among Turdidae family rather than between other passerines.
Pronounced MHC I gene diversity is essential for existence of species.
Our study signifies a valuable tool for the characterization of
evolutionary relevant difference across a population of birds with high
conservational concerns.
Keywords: MHC class I; Turdidae ; Adaptive immunity; Gene
flow; Genetic diversity; Polymorphic; Convergent evolution
1 INTRODUCTION
Major Histocompatibility Complex (MHC) are molecules encoded by certain
genes that are most polymorphic to have been described in vertebrates’
genomes [1]. Two types of MHC gene families, class I and class II,
which are useful cell surface glycoproteins that regulate the immune
response. MHC class II molecules are
heterodimers consists on α chain and a β chain, both contribute to
presenting peptides from the processing of extracellular pathogens such
as bacteria to the CD4+ T-helper cells [2].
Heterodimers molecules of MHC class
I are made up of an α chain and a non-MHC molecule, the β2
microglobulin. The α chain
constitutes a cytoplasmic tail, a transmembrane domain, and three
extracellular domains named α1, α2
and α3 [3] that are encoded by exons 2, 3 and 4. The MHC class I
molecules are expressed in almost all somatic cells and trigger an
adaptive immune response by presenting endogenously derived peptides of
viral protein and an individual’s own body cells to CD8+ cytotoxic
T-cells [4]. Polymorphism is largely confined within the region
encoding the ABS (Antigen Binding Site) of the MHC class I [5].
Maintenance of surprising diversity is supposed to be take place by two
types of selection: heterozygote advantage and frequency-dependent
selection. Heterozygotes could recognize a broader range of antigens
from multiple pathogens and therefore have more fitness than either
individual having homozygote [6]. Other is frequency-dependent
selection, in which rare alleles deliver a selective advantage where
pathogens have found a means to escape against common immune defensive
alleles in the population. Thus
alteration in pathogens community with time and locality result in MHC
variation in the host population. Generally, an individual possessing
huge numbers and diverse MHC alleles; more pathogens it can recognize
[1].
Structural diversity and immune response has been explored in numerous
research, including genomics [7, 8], ailment [9-11], mate choice
[12-14]. Sequence similarity at PBR based assignment to the locus is
frequently hampered by various evolutionary indicators due to current
recombination, duplication and/or concerted evolution as well as
positive selection mediated by a variety of pathogens [15]. Thus,
numerous studies emphasized MHC genes as important markers to evaluate
the adaptive potential and evolutionary status of threatened population
[16].
The emerging scenario inspires researchers to collect statistics from a
group of wild taxa to enlarge our understanding of the evolution of MHC
gene [17]. Despite significant efforts, protocols for locus-specific
MHC genotyping in avian are still difficult to achieve and remarkably
rare [18]. MHC studies in population of wild birds remain neglected
possibly due to complications in amplifying gene sequences from bird
species not closely related to systematically studied chicken [19,
20].
A significant decline in habitats and fragmentation of available
habitats are predisposing factors for dramatic deterioration in
population sizes [21].The avian genus Turdus is one of the
broadly distributed passerine genera, with 65 documented extant species.
The genus is listed wild territorial birds that are beneficial to china
having economic and research value. Birds of this genus are strongly
migratory thus experiencing a variety of environments. Up to the
present, there are no studies on MHC class I genes in Turdidaespecies, which is the first step towards exploring the role of selection
mediated by pathogens in the maintenance of MHC class I diversity.
Precisely, this study aims to (1) characterize locus-specific variation
in MHC I exon 3 genes across the Turdidae family and to examine
the mode of evolution by which such variation comes about. To achieve
this, we have measured the diversity and selection at MHC I genes to
make available the variations that exist across Turdidae family.
(2) We investigate the numbers of alleles possessed by each species and
the general features of alleles in terms of functional genetic
diversity. (3) Phylogenetic analyses to assess evolutionary
relationships and processes driving avian MHC I diversity among four
species of Turdidae family and other avian species. Results of
this study provide us an insight into the evolutionary processes
involved in avian MHC diversity, an important path for detailed studies
on avian MHC evolution.