Characterization o f Zebrafish Mutant m erlot as a Non-Mammalian Vertebrate Model for Congenital Anemia Due to Protein 4.1 Deficiency

Abstract

The zebrafish mutant merlot (mot) is characterized by onset o f a severe anemia at 96 hours post fertilization. We performed whole mount RNA in situ hybridization and showed that the process o f primitive erythropoiesis is not interrupted in the mot embryos. Blood analysis demonstrated that mot suffers from a severe congenital hemolytic anemia. Using the TU N E L assay, we detected apoptotic erythroid progenitors in the kidneys. We performed electron microscopic analysis and detected membrane abnormalities and a loss o f the cortical membrane organization in the mot cells. We used positional cloning techniques w ith a candidate gene approach to demonstrate that mot encodes the erythroid specific isoform o f protein 4.1R, a critical component o f the red blood cell membrane skeleton. Sequence analysis o f 4.IR cD N A detected nonsense point mutations in both alleles o f mot resulting in premature stop codons. We performed linkage analysis and transgenic rescue experiments to provide further confirmation that the molecular defect in the protein 4 .1R is the underlying cause o f anemic phenotype in mot fish. This study presents the zebrafish mutant merlot as the first characterized non-mammalian vertebrate model o f congenital anemia due to a defect in protein 4.1R integrity.