Loss of the RNA-binding protein Rbm15 disrupts liver maturation in zebrafish

Abstract

Liver organogenesis begins with hepatic precursors in the foregut endoderm, followed by hepatoblast specification, differentiation, outgrowth, and maturation for the formation of functional hepatocytes. Although several signaling pathways and critical factors that regulate liver specification, differentiation, and proliferation have been identified, little is known about how liver maturation is regulated. Here, we used a screen for mutations affecting liver development in zebrafish and identified a cq96 mutant that exhibits a specific defect in liver maturation. Results from positional cloning revealed that cq96 encodes an RNA-binding protein, Rbm15, which is an evolutionarily conserved Spen family protein and known to play a crucial role in RNA m6A modification, nuclear export, and alternative splicing. However, a function of Rbm15 in embryonic liver development has not been reported. We found that Rbm15 is specifically expressed in the liver after its differentiation. CRISPR/Cas9-mediated loss of rbm15 repressed hepatic maturation, but did not affect hepatoblast specification, differentiation, and hepatocyte proliferation and apoptosis. Additional experiments disclosed that the mTOR complex 1 (mTORC1) pathway is highly activated in rbm15-deficient hepatocytes. Moreover, rapamycin treatment partially restored normal hepatic gene expression as well as the nuclear location of the transcription factor Hnf4a. Taken together, these results reveal an unexpected role of Rbm15 in liver maturation.

Uricase-Deficient Larval Zebrafish with Elevated Urate Levels Demonstrate Suppressed Acute Inflammatory Response to Monosodium Urate Crystals and Prolonged Crystal Persistence

“…Expression analysis of uox in zebrafish using whole mount in situ hybridization (WMISH) showed expression at 2 dpf in the developing liver, with weaker diffuse expression in the head and along the horizontal myoseptum ( Figure 2 A). By 4 dpf, this expression pattern remained, with strong expression in the liver and weaker expression in extrahepatic tissues ( Figure 2 A), consistent with a previous study [ 38 ]. To generate the uox knockout line, we used CRISPR/Cas9 gene editing to target exon 2 and create a premature termination codon early in the transcript ( Figure 2 B).…”

Alternative RNA Splicing in Fatty Liver Disease

“…RBM15 binds to RNA to regulate post-transcriptional modifications (106) such as alternative RNA splicing, polyadenylation, and protein translation. RBM15 is not only essential for megakaryocyte differentiation (107), but also indispensable for liver development (74). Hu et al (74) found RBM15 was expressed in the liver during its differentiation, and depletion of RBM15 specifically suppressed hepatic maturation and caused liver failure but did not affect hepatocyte proliferation and apoptosis.…”

“…RBM15 is not only essential for megakaryocyte differentiation (107), but also indispensable for liver development (74). Hu et al (74) found RBM15 was expressed in the liver during its differentiation, and depletion of RBM15 specifically suppressed hepatic maturation and caused liver failure but did not affect hepatocyte proliferation and apoptosis. More studies are needed to understand the role of RBM15 in hepatic maturation and liver diseases.…”

Analysis and identification of m6A RNA methylation regulators in metastatic osteosarcoma

“…This indicates that RBM15-mediated m 6 A RNA methylation may be implicated in the immune infiltration of OS. RBM15 is a critical methyltransferase that regulates the fate of cellular mRNA molecules by catalyzing the formation of m 6 A in mRNA; it has been previously uncovered in cortical development, 22 liver maturation, 23 and Xist-mediated X chromosome inactivation. 24,25 It is worth noting that we downloaded mutation data from TCGA for mutant processing of SARC and found that RBM15 is mainly mutated in a RNA recognition motif (RRM) with a somatic mutation rate of only 0.84%.…”