GFP::MAI-1 (xmSi32) and MAI-1::mCherry (xmSi31) showed the same tissue localization. GFP::MAI-1 is expressed in specific somatic tissues in the nuclei and in the cytoplasm through specific tissues, including the cuticle, hypodermis, rectum, vulva and neurons. Although the expression pattern did not suggest a mitochondria network and MAI-1 does not carry a mitochondrial transport sequence, we tested whether MAI-1 was expressed in the mitochondria by incubating GFP:: MAI-1 with Mitotracker Red CMXRos and found no co-localization between the mitochondrial probe and GFP::MAI-1. These results demonstrate that MAI-1 is indeed not expressed in mitochondria but in the cytoplasm, as previously suggested Ichikawa et al. Additionally, we observed that GFP::MAI-1 is expressed in the nuclei.
MAI-2::GFP expression was observed in the cytoplasm at all the embryonic and post-embryonic stages in what seems to be a mitochondrial pattern. The expression of MAI-2::GFP was observed in the germline and all somatic tissues, including neurons, pharynx, the intestine, body wall muscle and the hypodermis, during C. elegans development. MAI-2::GFP co-localized with mitochondria in the gonad and embryos. We found a clear co-localization of MAI-2::GFP with the mitochondrial probe in the hypodermis and muscle.