Ectopic expression of the Aspergillus nidulans mitotic inducer, nimA kinase, in megakaryocytes:: Effect on polyploidization

Aspergillus nidulans nimA gene encodes a serine/threonine protein kinase (NIMA) whose activity is essential for mitotic entry and chromatin condensation. Both the activity and the abundance of NIMA protein increase at the G2/M transition of the fungal cell cycle. In this study, He report the effects elicited by ectopic expression of nimA on polyploidization in a mouse megakaryocytic line, Y10 which is undergoing an endomitotic cell cycle. A pool of Y10 stable transfectants that hale been induced to express nimA displayed a decrease in cell number and an elevated DNA content per cell. NIMA also dramatically, enhanced the activity of phorbal 12-myristate 13-acetate ton ard polyploidization. Analysis of individual nial. transfectants revealed that the DNA content per cell rose in tells expressing high levels of nimA and that the level of cyclin B nas reduced as compared to the mock-transfected cells. These effects observed in polyploidizing megakaryocytes are in contrast to those found in A. nidulans and HeLa cells, in which induced nimA expression caused abnormal chromatin condensation and cell cycle arrest. We conclude that high-level expression of nimA in cells programmed to undergo endomitosis could potentiate polyploidization. The challenge non resides in the isolation of the authentic megakaryocyte counterpart of the fungal nimA. (C) 1999 International Society for Experimental Published by Elsevier Science Inc.