Fuzzy Unheritance: A Novel Form Of Somatic Cell Inheritance That Regulates Cell Population Heterogeneity

Multi-level heterogeneity is a characteristic feature of cancer cell populations. However, how a cell population regulates and maintains its cell population heterogeneity is not well understood. Based on conventional theories of genetic inheritance, cell division is precise, where a daughter cell inherits an identical karyotype from its mother cell. Therefore, errors that are generated during cell division occur at low frequencies that take prolonged time periods to accumulate. However, the overwhelming heterogeneity found in unstable cancers is largely inconsistent with current models of genetic inheritance. In order to determine the mechanism of how heterogeneity is regulated, the pattern of inherited traits, including karyotype and growth rate, are compared in cell lines with different degrees of genome instability. Single cell and population-based assays were conducted and illustrate the following: 1) single unstable cells cannot pass a specific karyotype or growth rate and instead pass a heterogeneous array of karyotypes and growth rates; 2) genome heterogeneity is linked to other heterogeneous features of the system, like growth heterogeneity; 3) cells that are outliers dominate cell population dynamics when the cell population is unstable; and 4) the statistical average does not give an accurate portrayal of unstable cell populations. Altogether, this suggests that genome instability leads to genome replacement-mediated macro-cellular evolution that precludes the clonal expansion of a few abnormal cells; and 2) a given degree of heterogeneity can be inherited from a single cell. Because a given degree of heterogeneity is inherited, and the specific variants change between cell passages, this inheritance is termed fuzzy inheritance. According to fuzzy inheritance, rather than passing specific changes, the potential to generate genomic variation is passed. Fuzzy inheritance provides a cell population with the necessary evolvability and explains how heterogeneity is regulated and maintained in normal tissue and in cancer cells

Comparison of mitotic cell death by chromosome fragmentation to premature chromosome condensation

Mitotic cell death is an important form of cell death, particularly in cancer. Chromosome fragmentation is a major form of mitotic cell death which is identifiable during common cytogenetic analysis by its unique phenotype of progressively degraded chromosomes. This morphology however, can appear similar to the morphology of premature chromosome condensation (PCC) and thus, PCC has been at times confused with chromosome fragmentation. In this analysis the phenomena of chromosome fragmentation and PCC are reviewed and their similarities and differences are discussed in order to facilitate differentiation of the similar morphologies. Furthermore, chromosome pulverization, which has been used almost synonymously with PCC, is re-examined. Interestingly, many past reports of chromosome pulverization are identified here as chromosome fragmentation and not PCC. These reports describe broad ranging mechanisms of pulverization induction and agree with recent evidence showing chromosome fragmentation is a cellular response to stress. Finally, biological aspects of chromosome fragmentation are discussed, including its application as one form of non-clonal chromosome aberration (NCCA), the driving force of cancer evolution

Micronuclei and Genome Chaos: Changing the System Inheritance

Micronuclei research has regained its popularity due to the realization that genome chaos, a rapid and massive genome re-organization under stress, represents a major common mechanism for punctuated cancer evolution. The molecular link between micronuclei and chromothripsis (one subtype of genome chaos which has a selection advantage due to the limited local scales of chromosome re-organization), has recently become a hot topic, especially since the link between micronuclei and immune activation has been identified. Many diverse molecular mechanisms have been illustrated to explain the causative relationship between micronuclei and genome chaos. However, the newly revealed complexity also causes confusion regarding the common mechanisms of micronuclei and their impact on genomic systems. To make sense of these diverse and even conflicting observations, the genome theory is applied in order to explain a stress mediated common mechanism of the generation of micronuclei and their contribution to somatic evolution by altering the original set of information and system inheritance in which cellular selection functions. To achieve this goal, a history and a current new trend of micronuclei research is briefly reviewed, followed by a review of arising key issues essential in advancing the field, including the re-classification of micronuclei and how to unify diverse molecular characterizations. The mechanistic understanding of micronuclei and their biological function is re-examined based on the genome theory. Specifically, such analyses propose that micronuclei represent an effective way in changing the system inheritance by altering the coding of chromosomes, which belongs to the common evolutionary mechanism of cellular adaptation and its trade-off. Further studies of the role of micronuclei in disease need to be focused on the behavior of the adaptive system rather than specific molecular mechanisms that generate micronuclei. This new model can clarify issues important to stress induced micronuclei and genome instability, the formation and maintenance of genomic information, and cellular evolution essential in many common and complex diseases such as cancer