Meeting Abstract

S1.11  Monday, Jan. 4  Early vertebrate chromosome duplications and the evolution of the neuropeptide Y receptor gene regions LARHAMMAR, D; Uppsala Univ., Uppsala, Sweden Dan.Larhammar@neuro.uu.se

The early stages of vertebrate evolution involved major genomic events, namely two tetraploidizations before the gnathostome radiation. The time points for divergence of hagfishes and lampreys relative to the two tetraploidizations are still unclear. We have investigated several gene families that expanded in early vertebrate evolution, particularly the neuropeptide Y (NPY) family of peptides and the corresponding receptors (NPYR). The NPY peptide genes are located close to the homebox (Hox) gene clusters that quadrupled as a result of the tetraploidizations. The observation that lampreys have three NPY-family genes and probably more than two Hox clusters indicates that they have undergone two tetraploidizations, either the same ones as the gnathostomes or perhaps one shared and one independent. We are presently analyzing additional Hox/NPY-linked gene families that may shed light on lamprey divergence: voltage-gated sodium channels (SCN), insulin-like growth factor binding proteins (IGFBP), and activin receptors. The NPYR family is located in a different quartet of related chromosomes and has a more complex evolutionary history due to a local triplication before the tetraploidizations. We have shown that the ancestral gnathostome had seven NPYR genes, a situation still prevailing in sharks and amphibians. Other lineages have lost one or more NPYR genes. In lampreys only two NPYRs have so far been identified. Amphioxus does possess an NPY-like peptide but its receptor has not yet been confirmed. Tunicates seem to have lost the NPY system. More detailed studies of chromosomal locations in conjunction with sequence-based phylogenies are expected to elucidate the genomic events in early chordate evolution. (Supported by the Swedish Research Council and Carl Trygger’s Foundation.)