Forum de Estudantes de Biologia da Universidade do Porto

Estágio no Cibio - Genes MHC em tartarugas


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Estágio no Cibio - Genes MHC em tartarugas

Mensagem por Exaurido em Ter 27 Set 2011, 00:20

Title: Characterization of MHC genes and their variability in different species of turtles

Ylenia Chiari


The goal of this project is to characterize and study inter- and intra-specific variation in
the major histocompatibility complex (MHC) genes in distinct species of turtles (Phrynops
hilarii, Emys orbicularis, Caretta caretta, Chelonoidis nigra, Mauremys leprosa, Trachemys
scripta). The MHC plays a central role in the host immune response, and the level of diversity of
MHC genes is determined by both natural selection (i.e. the influence of disease) and
demography (i.e. population size, migration). MHC genes are among the most variable
functional genes known in vertebrates (Piertney & Oliver, 2006). The number of MHC genes and
their organization in the genome differs greatly among vertebrate lineages and species (i.e.
Kelley et al., 2005). Due to their role in the immune response, parasites serve as a selective
force, driving the differentiation of these genes even in closely related species (reviewed in
Kelley et al., 2005). In general, decreased variation at MHC loci has been observed in
endangered species that have undergone genetic drift or inbreeding due to severe reductions in
population size. However, studies on other threatened species show that natural selection
maintains a surprisingly high level of diversity in MHC genes (reviewed in Altizer et al., 2003).
Due to their utility for understanding the influence of disease in populations, numerous
studies of MHC genes have been conducted in a range of vertebrates. But, to this point, no
studies have been published on MHC in turtles and only a few in non-avian reptiles in general
(Grossberger & Parham, 1992; Madsen et al., 2000; Miller et al., 2006; Radtkey et al., 1996;
Wittzell et al., 1999).

To obtain MHC genes from turtles, genomic data (transcriptomes) already obtained by
next-generation sequencing from the above mentioned species will be used. A first screening of
all the genes recovered with this technique will be carried out for each species. As the MHC is
characterized by many genes and gene complexes, advanced laboratory work (RNA extraction,
RACE, PCR, and cloning) will be required to characterize the distinct genes and alleles for each
of the studied species. A comparison with MHC data already available for other vertebrates will
allow us to study the evolution of the MHC genes in reptiles and more specifically in turtles.
Furthermore, as for two of the selected species (Emys orbicularis and Chelonoidis nigra), a
population sampling is already available, investigation on the within species variation at the
studied genes will be carried out.

1) Isolate and characterize the MHC of distinct species of turtles from expressed mRNA. This
will allow us to target specific MHC genes in order to assess their level of variability in
populations of two of the studied species. In addition, basic information on MHC gene sequences
will facilitate future studies on MHC in other turtle species, especially those experiencing decline
due to pathogens (e.g. Gopherus or in Chelonia mydas).
2) Study the evolution of MHC genes in reptiles and turtles, looking at sites and genes under
selection, possible presence of gene rearrangements, and sites of high variability.
Methods and analyses that the student will learn and apply for this project
- RNA and DNA extraction
- 3’ and 5’ RACE
- Cloning
- Sequencing
- Sequence cleaning and alignment
- Phyologenetic analyses
- Analyses to identify genes and sites under selection

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    Data/hora atual: Qui 21 Mar 2019, 13:49