Pyknosis

Pyknosis, or karyopyknosis, is the irreversible condensation of chromatin in the nucleus of a cell undergoing programmed cell death or apoptosis ^[1]. It is followed by karyorrhexis, or fragmentation of the nucleus. Pyknosis is also observed in the maturation of erythrocytes (a red blood cell) and the neutrophil (a type of white blood cell). The maturing metarubicyte (a stage in RBC maturation) will condense its nucleus before expelling it to become a reticulocyte. The maturing neutrophil will condense its nucleus into several connected lobes that stay in the cell until the end of its cell life.