Molecular characterization of expressed DQA and DQB genes in the California sea lion ( Zalophus californianus )

Abstract

To date, there are no published MHC sequences from the California sea lion (Zalophus califomianus), a thriving species that, by feeding high on the marine food web, could be a sentinel for disturbances in marine and coastal ecosystems. In this study, degenerate primers and RACE technology were used to amplify near-fiiUThis study was supported by grants from the Office of Naval Resources (ONR), the Marine Community Foundation, the Fogarty International Center and the US National Science Foundation (#DEB-0094919) Studies were performed jointly in the laboratories of Stott and JohnsonThe nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the following accession numbers: An additional three Zaca-DQB sequences containing features compatible with pseudogenes or null alleles were also identified. Despite the identification of multiple DQA and DQB sequences, the degree of heterogeneity between them was extremely low. To confirm the limited degree of Zaca-DQ nucleotide variation between individuals, we used denaturing gradient gel electrophoresis to examine putative peptide binding region sequences from the peripheral blood leukocyte-derived RNAs of 19 wild-caught California sea lions from physically distinct populations. The pattern of Zaca-DQ sequence migration was identical between individuals and independent of geographical region. This apparent Zaca-DQ sequence identity between sea lions was confirmed by direct sequencing of individual bands. In combination, these fmdings raise important questions regarding immimogenetic diversity within this thriving species, and should prompt further research into the existence of a highly polymorphic sea lion class II MHC molecule with sequence features that support traditional peptide binding fiuictions.

Identification of the expressed MHC class II DQB gene of the Asiatic black bear, Ursus thibetanus, in Japan

“…The nucleotide sequence of the Urth-DQB coding region (to the stop codon: 798 bp) had a similarity with the California sea lion DQB (94%), dog DQB (90%) and human DQB (87%). Bowen et al (2002) reported that the California sea lion DQB amino acid sequences contained DQ-specific motifs of 3 amino acids in the exon 3 region. These motifs are especially useful for distinguishing the DQB from DRB sequences in several species of mammal.…”

“…1. Nucleotide sequences of the near full-length DQB cDNA (Urth-DQB) and DQB exon 2 region (Urth-DQB*a to Urth-DQB*e) of the Asiatic black bear (this study), California sea lion (Bowen et al, 2002) and the dog DQB sequences (Wagner, unpublished;Debenham et al, 2005). Dots indicate identity with the nucleotides of Urth-DQB.…”

“…Primer ZcDQBUEX1D, previously reported by Bowen et al (2002), was also used for 5'RACE-PCR. RACE-PCR amplification was carried out using a DNA Thermal Cycler in 25 μl reaction mixture containing 10 × Ex Taq Buffer, 2.5 mM dNTP Mixture, 2 pmol/μl of each primer and 0.625 Units of Ex Taq Hot Start Version (TaKaRa Bio Inc.).…”

Sequence Analysis of MHC Class II Genes in Cetaceans

“…Exactly how much MHC diversity is required to ensure long-term population viability remains a fundamental question in conservation genetics. A lack of variation at the MHC may increase the susceptibility of an isolated population to infectious disease epidemics, with potentially catastrophic consequences (Bowen et al, 2002). For example, a link between MHC diversity and an effective response to both pathogenic and toxicogenic challenges was proposed (Acevedo-Whitehouse et al, 2003).…”

“…The most diverse and extensively studied MHC genes are the DQB and DRB genes. Diversity of DQB or DRB genes has been characterized in many mammalian species such as primates (Bontrop et al, 1999), bank vole (Axtner & Sommer, 2004), domestic mammals (Schook & Lamont, 1996, Yuhki & O'Brien, 1997, Mikko et al, 1999, Wagner et al, 1999, and marine mammals (Murray et al, 1999, Bowen et al, 2002, 2004, Baker et al, 2006, Hayashi et al, 2006, Xu et al, 2007. After these studies on non-model free-ranging species were carried out, intriguing questions were raised about whether and how selection operates on the MHC of natural populations characterized by distinct pathogens and demographic and environmental conditions (Bernatchez & Landry, 2003;Sommer, 2005).…”