Amitosis

AMITOSIS (from the Greek a - negative particle, and mitos - thread; synonyms: direct division, fragmentation). This term refers to a special form of cell division that differs from ordinary mitosis (division with fibrous metamorphosis of the nucleus) in its simplicity. According to the definition of Flemming, who established this form (1879), "amitosis is such a form of cell and nucleus division in which the formation of a spindle and properly formed chromosomes and their movement in a specific order are absent." The nucleus, without changing its character, directly or after preliminary division of the nucleolus, splits into two parts by means of strangulation or the formation of a one-sided fold. Following the division of the nucleus in some cases, the cell body also divides, also by strangulation and cleavage. Sometimes the nucleus breaks into several parts of equal or unequal size. A. has been described in all organs and tissues in both vertebrates and invertebrates; for a time it was thought that protozoa divide exclusively by direct means, but the error of this view was soon demonstrated. The main criterion for confirming A. was the finding of binucleate cells, and along with them - cells with large nuclei showing folds and constrictions; amitotic division of the cell body was observed extremely rarely, it was necessary to conclude on the basis of indirect considerations. - Various views have been expressed on the essence and significance of A.: 1. A. is the primary and simplest method of division (Strassburger, Waldeyer, Carpow); it occurs, for example, during wound healing, when cells "do not have time" to divide by mitosis (Balbiani, Henneguy), it is sometimes observed in embryos (Maksimov). 2. A. is an abnormal method of division, occurs under pathological conditions, in dying tissues, sometimes in cells with enhanced secretion and assimilation and marks the end of divisions; cells after A. can no longer divide mitotically, therefore A. has no regenerative significance (Flemming, Ziegler, Rath). 3. A. does not represent a method of cell reproduction; in one set of cases A. is simply the disintegration of the nucleus under the influence of physico-mechanical factors (pressure, compression of the cell by something, formation and deepening of folds due to changes in osmotic pressure of the nucleus), in other cases described as A., there is an abortive (not completed to the end) mitosis; depending on the stage at which mitosis is interrupted, cells with a large strangulated nucleus or binucleate cells are obtained (Karpov).'- Over the last two decades, the question of A. has been debated less frequently, with all three views being expressed: thus, unity of views on A. has not been achieved.