The Ribosome Biogenesis Protein Nol9 Is Essential for Definitive Hematopoiesis and Pancreas Morphogenesis in Zebrafish.

Ewa Bielczyk-Maczyńska,Ana Cvejic,Derek L Stemple,Neha Wali,Steven A Harvey,Lauren Ferreira,Antonio Fernández-Pevida,Laure Lam Hung,Tobias Fleischmann,Inês Barroso,Alan J Warren,Félix Weis

doi:10.1371/journal.pgen.1005677

Abstract

Ribosome biogenesis is a ubiquitous and essential process in cells. Defects in ribosome biogenesis and function result in a group of human disorders, collectively known as ribosomopathies. In this study, we describe a zebrafish mutant with a loss-of-function mutation in nol9, a gene that encodes a non-ribosomal protein involved in rRNA processing. nol9 sa1022/sa1022 mutants have a defect in 28S rRNA processing. The nol9 sa1022/sa1022 larvae display hypoplastic pancreas, liver and intestine and have decreased numbers of hematopoietic stem and progenitor cells (HSPCs), as well as definitive erythrocytes and lymphocytes. In addition, ultrastructural analysis revealed signs of pathological processes occurring in endothelial cells of the caudal vein, emphasizing the complexity of the phenotype observed in nol9 sa1022/sa1022 larvae. We further show that both the pancreatic and hematopoietic deficiencies in nol9 sa1022/sa1022 embryos were due to impaired cell proliferation of respective progenitor cells. Interestingly, genetic loss of Tp53 rescued the HSPCs but not the pancreatic defects. In contrast, activation of mRNA translation via the mTOR pathway by L-Leucine treatment did not revert the erythroid or pancreatic defects. Together, we present the nol9 sa1022/sa1022 mutant, a novel zebrafish ribosomopathy model, which recapitulates key human disease characteristics. The use of this genetically tractable model will enhance our understanding of the tissue-specific mechanisms following impaired ribosome biogenesis in the context of an intact vertebrate.

Highlights

Ribosome biogenesis is a highly conserved and remarkably complex process that is essential for cell growth and proliferation
This study provides novel insight into the function of the ribosome biogenesis protein Nol9 in zebrafish development and presents a novel model that will help to decipher the tissue-specific mechanisms of ribosomopathies
It utilizes 60% of total cellular transcription in a growing yeast cell, with 2,000 ribosomes synthesized every minute [1]. It requires the coordinated action of all three RNA polymerases (RNAP I, II, III) and the synthesis of 4 ribosomal RNAs, 82 core ribosomal proteins (RPs), more than 200 non-ribosomal proteins and approximately 70 small nucleolar RNAs [2]

Summary

Introduction

Ribosome biogenesis is a highly conserved and remarkably complex process that is essential for cell growth and proliferation. It utilizes 60% of total cellular transcription in a growing yeast cell, with 2,000 ribosomes synthesized every minute [1]. It requires the coordinated action of all three RNA polymerases (RNAP I, II, III) and the synthesis of 4 ribosomal RNAs (rRNAs), 82 core ribosomal proteins (RPs), more than 200 non-ribosomal proteins and approximately 70 small nucleolar RNAs (snoRNAs) [2]. Ribosomopathies that present with hematological defects include Diamond Blackfan anemia (DBA), 5q- syndrome, Shwachman-Diamond syndrome (SDS) and T-cell acute lymphoblastic leukemia (T-ALL). Additional examples of ribosomopathies include Treacher Collins syndrome (TCS), isolated congenital asplenia (ICAS), aplasia cutis congenita (ACC), BowenConradi syndrome (BCS), North American Indian Childhood cirrhosis (NAIC) and alopecia, neurological defects and endocrinopathy (ANE) syndrome [4]

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