Fibrillarin homologs are required for divergent cell lineage development by translational regulation in planarian homeostasis and regeneration [Ribo-seq]
Translational regulation in adult regenerative tissue remains unclear. Planarians, renowned for remarkable cell turnover and tissue regeneration capabilities, are regenerative flatworms that provide an ideal model to address the gap in knowledge between translational control and cell turnover during adult tissue homeostasis and regeneration. Fibrillarin (FBL) is an RNA 2-O'-methyltransferase crucial for rRNA processing, playing a pivotal role in translational regulation. We explored this in planarian Schmidtea mediterranea and identified two FBL homologs: Smed-fbl-1 (fbl-1) and Smed-fbl-2 (fbl-2) are essential for homeostasis and regeneration, but have distinct roles. fbl-1 is enriched in neoblasts and essential for multiple progenitor cell differentiation. Conversely, fbl-2 is expressed in egr5+ epidermal progenitors, crucial for late-stage epidermal lineage specification. Knockdown (KD) of fbl-1 and fbl-2 resulted in different 2-O'-methylation patterns, suggesting their influence on specific mRNA translation during regeneration. Riboseq analysis revealed that fbl-1 KD reduced the translation of genes associated with alternative splicing, cell cycle, and DNA replication, while fbl-2 KD reduced the translation of genes related to protein stability. Interestingly, fbl-2+ cells spatially correlated with wnt-1+ cells, hinting at fbl-2's role in its localization. Our study indicated that duplicate fbl genes may have a compensatory role in the development of specific cell lineages. This finding underscores the significance of rRNA modification in translation regulation during the maintenance and regeneration of adult tissues. Overall design: To investigate translational and transcriptional regulation upon fbl KD, we established an approach to capture the translated mRNA  in planarian. 3 biological repeats of each experimental group (egfp, egfp 2x, fbl-1, and fbl-2).