Studies on Zebrafish Thrombocytes

Zebrafish thrombocytes exhibit characteristics of human platelets and megakaryocytes, making them valuable for studying megakaryopoiesis and thrombopoiesis. Using single-cell RNA sequencing, we analyzed gene expression in young and mature zebrafish thrombocytes. We identified 394 protein-coding genes unique to young thrombocytes, many corresponding with human orthologs, suggesting shared regulatory mechanisms in zebrafish and humans. We hypothesized knocking down these 394 genes should identify the novel regulatory genes that control thrombocyte maturation. To address this, we used the piggyback knockdown method to knock down these genes to study their biological functions in zebrafish thrombopoiesis. We first found the knockdown of nfe2, nfe2l1a, and nfe2l3 reduced both young and mature thrombocyte counts, confirming their role in thrombopoiesis. A comprehensive knockdown screening of the uniquely expressed genes in young thrombocytes identified 7 candidate genes associated with thrombopoiesis. We selected the spi1b gene for further mutant characterization, which revealed its critical role in young thrombocyte development, with homozygous mutations leading to embryonic lethality. Considering megakaryocyte properties in thrombocytes, we studied the potential for polyploidization in zebrafish thrombocytes. The inhibition of AURKA led to the development of polyploid thrombocytes resembling mammalian megakaryocytes, suggesting the retention of genetic programs for megakaryocyte development in zebrafish thrombocytes and providing insights into the evolutionary basis of thrombopoiesis. Thus, our study reveals critical gene expression patterns and regulatory factors in zebrafish thrombocyte development, offering insights into conserved mechanisms relevant to developmental biology and research in thrombosis and hemostasis disorder.