Genes for 5'mRNA cap binding proteins, eif4ea and eif4eb, have alternative roles during heart regeneration

All eukaryotes possess the essential mRNA cap-binding protein eIF4E, which initiates translation. This protein is highly conserved, with versions from zebrafish and humans able to rescue yeast. All fish also have an additional eIF4E family, called eif4e1c, which is crucial for heart regeneration. Deletion of eif4e1c leads to growth defects and impaired heart regeneration, but its unclear if similar effects occur when canonical translation mechanisms are disrupted. In this study, we deleted the two zebrafish paralogs of eIF4E, eif4ea and eif4eb. While individual deletions of these genes do not show the same phenotypes as eif4e1c deletion, compound mutants enhanced eif4e1c phenotypes, suggesting partial compensation by canonical eIF4E proteins in eif4e1c mutants. Surprisingly, unlike other eukaryotes, deleting both canonical mRNA cap-binding proteins did not result in lethality, and eif4e1c could fully compensate for eIF4E function. Although we anticipated that double mutants would regenerate hearts better since they contain eif4e1c alone, no improvement was observed in the double mutant. Interestingly, single deletions of eif4ea or eif4eb did improve heart regeneration. This supports a model where the balance between the eif4e1c and canonical pathways is crucial for stimulating heart regeneration.