SNS Marker Genes in Lamprey Embryonic Development Figure 4. Expression of Ascl1 during embryonic development of the lamprey. (A) Phylogenetic analysis places the putative lamprey Ascl1 ortholog with gnathostome Ascl1 genes. (B) Onset of Ascl1 expression is apparent at day 7, when transcripts are detected in the anterior lip mesoderm. Shortly afterwards (C), faint expression is observed in the lens (arrow). (D) On day 12, lens expression is elevated (arrow), and staining on the hypophysis and trigeminal ganglia (red arrow) are also observed. (E) Finally, on day 14, Ascl1 expression is observed in the notochord (red arrow). doi:10.1371/journal.pone.0026543.g004 give rise to the cardiac SIF cell aggregation [26]. Indeed, there is expression of Hand in ganglia adjacent to the heart (figure 3F), although Phox2 is not present in the same structures. However, at the stages examined, we failed to observe migratory precursors that might give rise to the scattered chromaffin cells that are said to occur throughout the lamprey body. PLoS ONE | www.plosone.org 6 October 2011 | Volume 6 | Issue 10 | e26543