Long isoform. We generated strains that express either long
(ex7+) or short
(ex7-) MBL-1 protein isoforms, tagged with mCherry, under both endogenous promoters together, and investigated their subcellular localization at the L4 larval stage (when most tissue development is complete). Expression of MBL-1 was detected in various tissues in a pattern consistent with previous studies [38, 39], specifically in the head and tail ganglia, the ventral nerve cord (VNC), the spermatheca, and the posterior gut. Consistent with the human longer MBNL isoform, mCherry signals showed a distinct nuclear localization when linked with long
(ex7+) isoforms, most noticeably in, but not limited to, cells of the gut and the head region. In contrast, short
(ex7-) isoforms showed a more diffuse pattern, consistent with localization both in the nucleus and cytoplasm. We note that the expression in the gut might be ectopic and a possible consequence of the presence of the
unc-54 30-UTR, as reported before [43].