Meeting Abstract
S1.8 Monday, Jan. 4 Midline signaling and the evolution of the lamprey forebrain RETAUX, S*; OSORIO, J; GUERIN, A; XIAO, JH; KANO, S; CNRS Institut A. Fessard, Gif sur Yvette, France; CNRS Institut A. Fessard, Gif sur Yvette, France; CNRS Institut A. Fessard, Gif sur Yvette, France; CNRS Institut A. Fessard, Gif sur Yvette, France; CNRS Institut A. Fessard, Gif sur Yvette, France retaux@inaf.cnrs-gif.fr
The forebrain is the brain region which has undergone the most dramatic changes through vertebrate evolution. Analyses conducted in lampreys are essential to gain insight into the broad ancestral characteristics of the forebrain at the dawn of vertebrates, and to understand the molecular basis for the diversifications that have taken place in cyclostomes and gnathostomes following their splitting. We have studied the embryonic expression patterns of 43 lamprey genes, coding for factors involved in cell proliferation, stemcellness, neurogenesis, patterning and regionalization in the developing forebrain. Systematic comparisons with model organisms highlight conservations likely to reflect shared features present in the vertebrate ancestors. They also point to changes in midline signaling systems –pathways which control the growth and patterning of the neuroepithelium-, which may have been crucial in the evolution of forebrain anatomy at the origin of vertebrates. We have therefore investigated further the regulation one of them, the Hedgehog (Hh) system. Genomic analyses in the river lamprey L. fluviatilis and the sea lamprey P. marinus were performed. Long-distance alignments and phylogenetic footprinting, together with local alignment of putative regulatory motifs show that lamprey Hhs do share non-coding regulatory elements with other vertebrates Hhs, however with significant divergence. Thus, lamprey Hh genes have evolved in a “lamprey-specific” way ever since the split between the last common ancestor of cyclostomes and gnathostomes, and allow discussing the emergence of conserved non coding regulatory sequences in vertebrate genomes.
