Runt-homologous molecules are characterized by their DNA binding runt-domain which is highly conserved within bilaterians. The three @entity1 runt-genes are master regulators in cartilage/bone formation and @entity1210 . Historically these features evolved in Craniota and might have been promoted by runt-gene duplication events. The purpose of this study was therefore to investigate how many runt-genes exist in the stem species of chordates, by analyzing the number of runt-genes in what is likely to be the closest living relative of Craniota- @entity23251 . To acquire further insight into the possible role of runt-genes in early chordate evolution we have determined the number of runt-genes in sea urchins and have analyzed the runt-expression pattern in this species. Our findings demonstrate the presence of a single runt-gene in @entity23251 and sea urchin, which makes it highly likely that the stem species of chordates harbored only a single runt-gene. This suggests that runt-gene duplications occurred later in chordate phylogeny, and are possibly also associated with the evolution of features such as @entity1210 , cartilage and bone development. In sea urchin embryos runt-expression involves cells of endodermal, mesodermal and ectodermal origin. This complex pattern of expression might reflect the multiple roles played by runt-genes in mammals. A strong runt-signal in the gastrointestinal tract of the sea urchin is in line with runt-expression in the intestine of @entity2199 and in the @entity19 gastrointestinal tract, and seems to be one of the phylogenetically ancient runt-expression domains.

A single XXXX and sea urchin runt-gene suggests that runt-gene duplications occurred in early chordate evolution.

@entity1 :: ('9606', 'Species') :: ['mammalian'] @entity2199 :: ('6239', 'Species') :: ['nematodes'] @entity19 :: ('10090', 'Species') :: ['murine'] @entity23251 :: ('7740', 'Species') :: ['amphioxus'] @entity1210 :: ('MESH:C536227', 'Disease') :: ['hematopoiesis']
@entity23251 :: (7740,Species) :: ['amphioxus']
