Hoxd-4Expression during Pharyngeal Arch Development in Flounder (Paralichthys olivaceus) Embryos and Effects of Retinoic Acid on Expression

Abstract

Teleost fish develop seven pharyngeal arches (mandible, hyoid and five gill arches) which give rise to the jaw and gills, and skeletal cell populations which originate from the cranial neural crest. The anterior border of expression of the Deformed (Dfd) group is located in the hindbrain and pharyngeal region. To investigate pharyngeal skeletal formation in the teleost fish, we cloned the cDNA coding Hoxd-4 from a cDNA library for flounder (Paralichthys olivaceus) embryos, and analyzed gene expression pattern during embryogenesis and the effects of retinoic acid (RA) on this gene expression. Between the 21-somite and prim-5 stages, Hoxd-4 was expressed in the central nervous system from rhombomere 7 to the spinal cord, and in the pharyngeal region posterior from gill arch 2. Its expression then became restricted to cartilage precursor cells of gill arches 2-5. When embryos in the early shield stage were exposed to RA at concentrations above 10(-7) M, the anterior border of Hoxd-4 expression shifted anteriorly in a dose-dependent manner, both in the central nervous system and pharyngeal region. We propose that, during gill skeleton formation, Hoxd-4 functions in the specification of regional identity between gill arches 1 and 2, and that their identity is affected by treatment with RA.

Developmental Roles of Pufferfish Hox Clusters and Genome Evolution in Ray-Fin Fish

“…In fugu, Hoxd4a is expressed with a sharp anterior boundary at hindbrain rhombomeres r6/r7 (Fig. 5h) as it is in tetrapods, zebrafish, and flounder (van der Hoeven et al 1996;Prince et al 1998b;Suzuki et al 1998;Nolte et al 2003). The duplicate gene Hoxd4b, however, is expressed with a more caudal anterior border (Fig.…”

The duplication of the Hox gene clusters in teleost fishes*1

“…Common carp (Cyprinus carpio) [65], Trout (Oncorhynchus sp.) [43], a flounder Paralichthys olivaceus [66,67]. Finally, fragments of Hox genes of the following teleosts were found in Genbank: Ictalurus punctatus, Salvelinus alpinus.…”

Retinoic Acid Isomers Produce Malformations in Postembryonic Development of the Japanese Flounder, Paralichthys olivaceus

“…In Japanese flounder, RA treatment at the hatching period has been shown to disturb pharyngeal cartilage development by affecting the expression of sonic hedgehog ( shh ) at the pharyngeal endoderm, resulting in specific malformations (Suzuki et al ., 1998(Suzuki et al ., , 1999. Shh expression was detected in the lower jaw at the B stage by RT-PCR, but the expression level was not affected by RA (data not shown).…”

“…Exposure of embryos at later stages than those affecting hindbrain development causes cleft palate and shortening of the facial processes in rat embryos (Morriss, 1972) and shortening of the frontnasal and maxillary processes in the chick (Wedden and Tickle, 1988). And RA treatments have been shown to cause facial malformations in flounder embryos (Suzuki et al ., 1998(Suzuki et al ., , 1999(Suzuki et al ., , 2000b. However, there have been few reports on the effects of RA on postembryonic development in teleosts.…”