Molecular characterization of the prostaglandin E receptor subtypes 2a and 4b and their expression patterns during embryogenesis in zebrafish

The molecular expression profiles of zebrafish ep2aand ep4bhave not been defined to-date. Phylogenetic treesof EP2a and EP4b in zebrafish and other speciesrevealed that human EP4and zebrafish EP4b were more closely related than EP2a. ZebrafishEP2a is a 281amino acid protein with high identity to that of human (43%), mouse (44%), rat (43%),dog(44%), cattle(41%), and chicken (41%). ZebrafishEP4bencoded a precursor of 497amino acids with high amino acid identity to that of mammals, including human (57%), mouse (54%), rat (55%), dog (55%), cattle (56%), and chicken (54%). Whole-mount in situ hybridizationrevealed that ep2awas robustly expressed in the anterior four somitesat the 10-somites stages, but was absent in the somites at 19 hpf.Itwas observedagainin the pronephric duct at 24 hpf, in the intermediate cell masslocated in the trunk, and in the rostral blood island at 30 hpf. Ep2awas also expressed in the notochordat 48 hpf. During somitogenesis, ep4bwas highly expressed in the eyes, somites, and the trunk neural crest. From 30 to 48 hpf, ep4bcould be detected in the posterior cardinal vein and the neighboring ICM. From these data, we conclude that ep2aand ep4bare conserved in vertebrates and that the presence of ep2aand ep4btranscripts during developmental stages infers their role during early zebrafish larval development. In addition, the variable expression of the two receptor isoforms wasstrongly suggestive of divergent roles of molecular regulation.