CRM1-mediated nuclear export is present during porcine embryogenesis, but is not required for early cleavage

Regulated movement of cellular factors between the cytoplasm and nucleus is required for fundamental cellular processes ranging from cell cycle control to transcriptional regulation. CRM1 is a nuclear export factor whose function is to actively transport nuclear cargos that bear nuclear export sequences to the cytoplasm. Because CRM1 likely plays a role in the intracellular regulation of many cellular processes, we set out to characterize CRM1 function during early mammalian embryogenesis. A series of embryo culture experiments that employed a specific inhibitor of CRM1, leptomycin B, indicated that CRM1 function is not required for development until after the 4-cell stage of porcine embryo development. Immunolocalization of CRM1 in fixed embryos revealed that CRM1 is localized in a unique pattern during the period of time when the embryo does not have a developmental requirement for CRM1. Despite these findings, a microinjection assay showed that CRM1 function persists during this period of development. This demonstrates that although CRM1 is present in a functional form throughout mammalian embryo development, its function is not required for early cleavage.