Differential mRNA localization of karyopherin-β2 homologs in C. elegans and humans

In Caenorhabditis elegans embryos, the nuclear transport receptor IMB-2 (Importin Beta Family-2, a karyopherin {beta}2) preferentially localizes to the nuclear envelope along with its encoding mRNA. This suggests that imb-2 mRNA is locally translated at the nuclear envelope. To test whether imb-2's two putative human orthologs, Transportin 1 (TNPO1) and Transportin 2 (TNPO2), exhibited similar mRNA localization, we performed smiFISH and microscopy in U2OS, HeLa, and human pluripotent stem cells. Neither human TNPO1 nor TNPO2 mRNA localized to the nuclear envelope in any tested human cell type. However, the human TNPO1 protein and the C. elegans IMB-2 protein both localized to the nucleus and its periphery. This suggests that despite their shared functional roles these karyopherins have different routes to expression.