Poster Presentation Society for Molecular Biology and Evolution Conference 2016

Tracing the presence of an enzyme essential for de-novo biosynthesis of NAD in the avian lineage: A case study for missing sequences in bird genomes (#527)

Toni I Gossmann 1 , Ines Heiland 2 , Falk Hildebrand 3 , Marc Niere 4 , Veronika N Laine 5 , Nicola Hemmings 1 , Mathias Ziegler 4
  1. APS, University of Sheffield, Sheffield, UK
  2. Arctic University of Norway, Tromsø, Norway
  3. EMBL, Heidelberg, Germany
  4. University of Bergen, Bergen, Norway
  5. NIOO-KNAW, Wageningen, Netherlands

The crucial role of NAD as a cofactor in redox reactions has long been known, but in recent years the involvement of this dinucleotide in a multitude of important regulatory processes and its direct medical implications for cancer and diabetes has led to a vast number of NAD-related studies in molecular biology and medical research. Quinolinate (QA) phosphoribosyl transferase (QAPRT) is the enzyme that is essential for the de-novo synthesis of NAD. In contrast to other vertebrate species, to date there is no evidence for the presence of QAPRT in any bird, even though all required up- and downstream enzymes of the NAD metabolic network are present, as deduced from available avian genomes. There are at least two hypotheses that could explain this observation. (1) QAPRT encoding genes are absent from avian genomes - and QAPRT function is compensated either directly by another enzyme or absent due to regulatory plasticity. (2) QAPRT has not been identified in the avian lineage because it is encoded in a genomic region that is difficult to assemble. To address the latter hypothesis, we used available bird whole-genome and transcriptome resources to extensively scan for sequences potentially coding for QAPRT. We found evidence that indicate the genomic presence and expression of the gene. We validated our results by an in-vitro functional essay. We further identified more than two thousand human genes for which no counterpart in most bird genomes has been identified to date and show that these genes are characterized by an extreme GC sequence composition. Taken together these results suggest that there is an annotation bias of bird genomes, potentially caused by the heterogeneous karyotype and sequence features common to all bird genomes.