Ribosomal proteins in zebrafish haematopoiesis and human disease

Abstract

Several congenital disorders of human haematopoiesis including Diamond- Blackfan anaemia result from heterozygous loss of genes involved in ribosome biogenesis. Further, hemizygosity for ribosomal protein gene RPS14 has been implicated in the pathogenesis of myelodysplastic syndrome with loss of 5q, suggesting that genes involved in ribosome biogenesis may act as both haploinsufficient tumour suppressors and regulators of normal haematopoiesis. Ribosome biogenesis is highly conserved through evolution and readily studied in simple organisms such as yeasts. However the zebrafish provides a wellestablished genetic model system which is ideally suited to rapid assessment of vertebrate haematopoiesis. I have therefore used the zebrafish to study genes involved in ribosome biogenesis and their effects on developmental haematopoiesis relevant to human disease. Presented in this work is investigation of the effect of disruption of 4 genes known to be involved in ribosome biogenesis on zebrafish haematopoiesis. Firstly, I describe a gene, Dead-box 18 (ddx18), identified in a forward genetic screen, whose disruption results in defective haematopoiesis and embryonic lethality. Secondly, I have studied the effects of loss of zebrafish orthologues of the human nucleophosmin gene (NPM1), the most frequently mutated gene in human acute myeloid leukaemia. Loss of Npm1 resulted in aberrant numbers of myeloid cells. Heterologous overexpression of mutated NPM1(NPMc+) resulted in increased production of haematopoietic stem cells suggesting a role for NPMc+ in pathogenesis of AML. Finally, I have shown that loss of Rps14 and Rps19 result in anaemia in developing zebrafish and have investigated p53-independent mechanisms for this effect. The findings described herein demonstrate that disruption of normal ribosome biogenesis frequently results in abnormal developmental haematopoiesis. Further genetic assessment of these tissue-specific pathways deregulated by loss of normal ribosome function may represent an important common mechanism underlying the pathogenesis of congenital and acquired disorders of haematopoiesis, and may provide novel pathways for therapeutic targeting.