The In Vivo Inactivation of MASTL Kinase Results in Thrombocytopenia.

Previously in our lab, a missense mutation in the MASTL (FLJ14813) gene on human chromosome 10 was linked to an autosomal dominantly inherited thrombocytopenia in a single pedigree. The mutation results in an amino acid change from glutamic acid at position 167 to aspartic acid and correlates with the inheritance of the disorder in all the affected individuals. The patients present with mild thrombocytopenia with an average platelet count of 60,000 platelets per microliter of blood. Northern blot analysis indicates that MASTL mRNA is restricted in its expression to hematopoietic and cancer cell lines. Functional studies presented here demonstrate a direct relationship between the transient knockdown of the Microtubule Associated Serine/Threonine Like (MASTL) kinase expression and the reduction of circulating thrombocytes in zebrafish (Danio rerio) while erythrocytes development normally. This transient knockdown of MASTL in zebrafish correlates with a decrease in the expression of the thrombopoietin receptor, c-mpl, and the CD41 platelet adhesion GpIIb protein but has no effect on essential housekeeping zebrafish gene, EF1α. The transient expression of a fluorescent protein fused to MASTL and E167D MASTL kinase demonstrates that MASTL localizes to the nucleus of cells as determined by confocal microscopy and TO-PRO-3 counterstain.