Differentiation trajectories in normal and malignant cells

Age dependent and cellular origin (stem versus progenitor) of a selected group of spontaneous brain tumors in humans

The origin of spontaneous human brain tumors has been recently debated as originating from a stem rather than a progenitor cell. Based on the statistical distribution of a selected group of primary brain tumors, and on the clonality and field theory for cancer growth, we propose as plausible the contribution of progenitor cells in the origin of the most common brain tumors such as, pediatric, mixed (glial and neuronal), and the aggressive glioblastoma multiforme in adults. Operationally, stem cell is defined as having a renewal probability of p=1, a progenitor 0<p<1, and a terminally differentiated cell as p=0. The space-time field location (microenvironment, cell-cell interactions...) and mitotic potential of a cell limits the distinguishability between stem and progenitors, due to the interconvertibility of these states via the process of retrodifferentiation (dedifferentiation). If excessively iterated retrodifferentiation of a mitotically competent cell prompts such a cell to organize programs that are atypical vis-à-vis the standard ones. Regarding specifically malignant cells, aperiodic cycles of dedifferentiation favour emergence of subclonal populations whose anachronistic evolution might become idiosyncratically resistant to therapies previously efficient against the initial tumoral mass. Unfortunately the "ab initio" identification of such subclonal "drifters" is impaired by systematic uncertainties as quali-quantified in appendix.

Euchromatinization of mammalian nuclei

This paper discusses a mechanism for converting heterochromatin into the more relaxed state of euchromatin. Actuation of such state conversion stems from disassembly of internal vesicles that are incapable of surviving when trapped within the inner chamber of mammalian nuclei.

Go and chemoresistance of malignant cells

In general terms the paper discusses the relevance of mitotically quiescent, malignant cells for increasing resistance to chemotherapy. Detailed are some routes to Go for malignancies either dependent or autonomous for their mitotic potential.

Transformation of myeloid cells with atypical renewal

The paper discusses malignant transformation of myeloid precursors that had atypical renewal in vivo. Their in vitro transformation rate disproportionates clinical incidences. Besides composition differences of transforming agents, this is due to quali-quantitative deficiencies of multitask growth factors added to empirical cultures. In combination these anomalies perturb the web of differentiation path, whose robustness minimizes clonal transformation in vivo.

A simplified approach to the statistical incidence of myeloid and erythroid leukemias in humans

Using order parameters from field theory, the paper rationalizes the statistics of myeloid and erythroid leukemias more satisfactorily than the random mutation hypothesis. Adapted to B- and plasma cell lineages, the same arguments conceptualize the statistics of related malignancies congruently to clinical findings.

A preliminary comment on the inversion of chromatid segments

In rare occasions, cancer cells have chromatids with segments stacked in inverted order vis-a-vis their normal counterparts. The paper discusses a mechanism for these anomalies as well as for their statistical incidences. The proposed mechanism and its telenomic implications have been adapted from ideas discussed in a preceding note.

Transcriptional entrainment between master-slave genes via sister chromatid exchanges

The paper discusses a mechanism for the coordination of a differentiation path through activation of slave genes by transcriptional complexes (excitons) organised by master genes. Entrainment occurs when master-slave genes form partnerships of closely apposed entities. Sister chromatid exchanges provide the action necessary for successful entrainment. Although concerned mainly with normal hematopoietic (stem) cells, the model applies also to certain leukemic cells, regarding in particular retrodifferentiation back to the stem state followed by attenuation of malignancy.

Sister chromatid exchange (SCE) of the kinetochore carrying segment, KS

The mechanism of SCE discussed in previous papers (3, 4) is adapted to account for the absence of kinks on chromatids experiencing an exchange limited to their KSs. The paper ends with a brief digression on kinks. Equivalent to solitons, such dynamic malformations can function as carriers of information along the chromatid stack.

Precipitous stem cell (SC) differentiation and 1/f noise

After a brief digression on certain types of noise of generic interest, it is concluded that 1/f noise offers interesting interpretations for unusual modes of SC differentiation such as the precipitous maturation of a subset of the macrophage lineage. Functionally equivalent to weak, spurious sources these specialized cells support the proliferation and maturation of erythroid cells extending thus the stimulatory influence of true, strong sources although in a rather indirect fashion.

On the handedness of the scaffolds of sister chromatids

We discuss a mechanical model for the mirror-symmetric inversion of the scaffold's helicity of replicated chromatids vis-a-vis that of their templates. The paper ends with comments on the orientability of certain genes and on the effects of such topologies upon (a)symmetric gene expression, in general. Our model and its generalizations apply only to the special subclass of 'coiled' chromatids whose statistical distribution in the genome of normal and of malignant cells is not known precisely.

Scaling concepts in cellular and subcellular dynamics

After developing a map for certain states typical of hemopoietic stem cells (SCs), we identify a number of parameters (e.g. fractal dimensions, oscillatory behavior in a multistable landscape, etc.) that scale down to subcellular structures such as interphase genome, chromatids, chromatin entanglements and DNA segmental motions. A curious aspect is the continuous reappearance of recursive processes even at very small biologic scales. These iterations are relevant not only for the normal behavior of (hemopoietic) cells but also for amplifying hidden genomic singularities above some critical threshold. When that happens, there are sudden quali-quantitative and often clonal changes in the cell behavior. As illustrated by specific leukemic cases, many paradoxes of malignant growth seem best explained by the peculiar sensitivity to initial condition of (hemopoietic) cells. Interpreted as chaotic oscillators, these cells display a spectrum of disorders that, in spite of appearing as random, are in fact triggered by amplification of subtle preconditions with statistico-deterministic outcomes, that are predictable within certain time limits.

On the myeloblast as initiator of certain human leukemias

We reconsider the proposal that a stem cell (SC) is the initiator of clonal (human) leukemias. Using chronic myeloid leukemia (CML) as an example, we discuss some conceptual and experimental inconsistencies of the above conjecture. As an alternative, it is proposed that CML is initiated by an immature myeloblast. The main idea is that CML results from certain growth-related accidents encountered along the myeloid differentiation path. Retrodifferentiation of (semi) autonomous myeloblasts back to the SC state seems the principle cause for the distribution of clonal markers across all hemopoietic lineages, including those that are not involved in the leukemic process.

On the topology of normal chromatids and on their translocations in myelogenous leukemia

After some comments on the topology of chromatids, restructuring of the interphase nucleus is conjectured to depend upon the nuclear vesicle apparatus. These vesicles change the intrinsic shape of chromatids to fit the different topology of the interphase nuclear spheroid. Reciprocal translocations between selected chromatids result whenever the nucleus of malignant cells organizes de novo certain exceptional or emergency differentiation paths. However, the almost unavoidable chimeric genes resulting from these translocations may be less ominous than hitherto suspected. This seems to be the case for chronic myelogenous leukemia, where the bcr-abl chimeric gene lessens the aggressiveness of the primary clone when functioning in the context of myelomonocitic differentiation. Finally, our model estimates the statistical incidences of the bcr-abl chimera. These estimates are found to agree with clinical data better than evaluations from the random mutation theory.