Nucleolin loss of function leads to aberrant Fibroblast Growth Factor signaling and craniofacial anomalies

Abstract

Ribosomal RNA (rRNA) transcription and ribosome biogenesis are global processes required for growth and proliferation of all cells, yet perturbation of these processes in vertebrates leads to tissue-specific defects termed ribosomopathies. Mutations in rRNA transcription and processing proteins often lead to craniofacial anomalies; however, the cellular and molecular reasons for these defects are poorly understood. Therefore, we examined the function of the most abundant nucleolar phosphoprotein, Nucleolin (Ncl), in vertebrate development. ncl mutant (ncl−/−) zebrafish present with craniofacial anomalies such as mandibulofacial hypoplasia. We observed that ncl−/− mutants exhibited decreased rRNA synthesis and p53-dependent apoptosis, consistent with a role in ribosome biogenesis. However, we found that Nucleolin also performs functions not associated with ribosome biogenesis. We discovered that the half-life of fgf8a mRNA was reduced in ncl−/− mutants, which perturbed Fgf signaling, resulting in misregulated Sox9a-mediated chondrogenesis and Runx2-mediated osteogenesis. Consistent with this model, exogenous FGF8 treatment significantly rescued the cranioskeletal phenotype in ncl−/− zebrafish, suggesting that Nucleolin regulates osteochondroprogenitor differentiation. Our work has therefore uncovered tissue-specific functions for Nucleolin in rRNA transcription and post-transcriptional regulation of growth factor signaling during embryonic craniofacial development.

Quantitative proteomics reveals the dynamic proteome landscape of zebrafish embryos during the maternal-to-zygotic transition

“… 59 Nucleolin (Ncl) involved in RNA binding modulates ribosomal RNA (rRNA) transcription and post-transcriptional regulation in zebrafish embryos. 60 Zc3h14 is a polyadenosine [poly(A)] RNA-binding protein and controls the proper length of poly(A) tails. 61 Zc3h14 also regulates pre-mRNA processing of some mRNA transcripts and modulates cellular energy levels.…”