Differential expression of the glyceraldehyde-3-phosphate dehydrogenase gene family in the nematode Caenorhabditis elegans
The differential expressions of the glyceraldehyde-3- phosphate dehydrogenase (GAPDH) gene family and their mRNA localizations in the nematode Caenorhabditis elegans were studied. Two tandemly linked direct-repeat GAPDH genes, gpd- 2 and gpd-3 , were isolated and sequenced. Compared with the two identical previously cloned GAPDH genes gpd-1 and gpd-4, gpd-2 and gpd-3 have slightly different structures regarding the locations of introns and the encoded amino acids. Northern blot analysis of total RNAs isolated from worms at different developmental stages shows that gpd-1 and gpd-4 are coordinately expressed and their transcripts are enriched in embryos which are predominantly composed of non-muscle cells. gpd-2 and gpd-3 are also coordinately transcribed, but show greater post-embryonic expression. Results of in situ hybridization with biotinylated asymmetrical DNA probes indicate that gpd-1 and gpd-4 mRNAs are present in all cells in small amounts. In contrast, gpd-2 and gpd-3 mRNAs are specifically localized within the actin-containing zones of body-wall muscle cells. These results suggest that gpd-1 and gpd-4 encode for the embryo-enriched minor isoenzyme GAPDH-I, while gpd-2 and gpd-3 encode for the body-wall muscle specific isoenzyme GAPDH-2. In addition, the actin genes act-1 and act-3 were shown to encode body-wall specific mRNAs that were also localized to the thin myofilaments.