O. Mokady et al., OVER ONE-HALF BILLION YEARS OF HEAD CONSERVATION - EXPRESSION OF AN EMS CLASS GENE IN HYDRACTINIA-SYMBIOLONGICARPUS (CNIDARIA, HYDROZOA), Proceedings of the National Academy of Sciences of the United Statesof America, 95(7), 1998, pp. 3673-3678
We report the isolation of an empty spiracles class homeodomain-contai
ning gene, Cn-ems, from the hydrozoan Hydractinia symbiolongicarpus, t
he first gene of this class characterized in a lower metazoan, Cn-ems
was found to be expressed in the head of gastrozooids, specifically in
endodermal epithelial cells of the taeniolae of the hypostome, Cn-ems
is not expressed in gonozooids, which lack taeniolae, Experimental co
nversion of the posterior region of the planula larva into head struct
ures up-regulates expression of the gene, These findings establish tha
t the association of ems-class genes with head structures preceded the
evolution of bilateral symmetry.