Functional analysis of mitogen-activated protein kinase-3 (MAPK3) and its regulation of the promoter region in zebrafish.

Mitogen-activated protein kinase (MAPK) plays a pivotal role in intracellular actions in response to a variety of extracellular stimuli. Real-time reverse-transcription polymerase chain reaction analysis of MAPK3 tissue distribution in zebrafish showed significant differences in the fin and liver compared with muscle. A 1.2-kilobase (kb) pair and a 2.3-kb fragment of the 5'-flanking region displayed minimal promoter activity in the zebrafish liver (ZFL) and HeLa cell lines after treatment with insulin-like growth factors (IGF-I and IGF-II). Targeted knockdown of the MAPK3 gene by two antisense morpholino oligonucleotides revealed that although the zebrafish MAPK3 MO 1-targeted sequence was located at 5' untranslated region and the zebrafish MAPK3 MO 2-targeted sequence was located in the mature peptide region, similar results were shown in zebrafish for disruption of notochord development, with the whole body exhibiting distortion. From a comparative point of view, this study of the MAPK3 gene in zebrafish might not correlate well with previously published studies on mice. These molecular results suggest that MAPK3 plays an important role in whole-body development and is required for general embryonic development. Finally, MAPK3 may play important roles in fish cell growth.