Multipotent stem cell (CFU-S) numbers and circadian variations in aging mice

Circadian oscillators in eukaryotes

The biological clock, present in nearly all eukaryotes, has evolved such that organisms can adapt to our planet's rotation in order to anticipate the coming day or night as well as unfavorable seasons. As all modern high-precision chronometers, the biological clock uses oscillation as a timekeeping element. In this review, we describe briefly the discovery, historical development, and general properties of circadian oscillators. The issue of temperature compensation (TC) is discussed, and our present understanding of the underlying genetic and biochemical mechanisms in circadian oscillators are described with special emphasis on Neurospora crassa, mammals, and plants.

The 4th dimension and adult stem cells: Can timing be everything?

The rotation of the earth on its axis influences the physiology of all organisms. A highly conserved set of genes encoding the core circadian regulatory proteins (CCRP) has evolved across species. The CCRP acts through transcriptional and post-transcriptional mechanisms to direct the oscillatory expression of genes essential for key metabolic events. In addition to the light:dark cycle, the CCRP expression can be entrained by changes in feeding and physical activity patterns. While mammalian CCRP were originally associated with the central clock located within the suprachiasmatic nucleus of the brain, there is a growing body of evidence documenting the presence of the CCRP in peripheral tissues. It is now evident that the CCRP play a role in regulating the proliferation, differentiation, and function of adult stem cells in multiple organs. This concise review highlights findings concerning the role of the CCRP in modulating the adult stem cell activities. Although the manuscript focuses on hematopoietic stem cells (HSCs), bone marrow-derived mesenchymal stem cells (BMSCs), adipose-derived stem cells (ASCs) and cancer stem cells, it is likely that the contribution of the CCRP merits consideration and evaluation in all stem cell pathways.

Cytometry and time-dependent variations in peripheral blood and bone marrow cells: a literature review and relevance to the chronotherapy of cancer

By flow cytometry of individual cells, multiple cell properties can be analyzed. Such parameters may be important in relation to cytotoxic treatment of cancer. For example, DNA measurements will answer questions regarding cell kinetics. Myelosuppression is the major dose-limiting toxicity during cancer treatment. Therefore, the study of cell cycle parameters in bone marrow cells is highly relevant. However, inattention to the existence and potential importance of biological rhythms may introduce artifacts and misleading results. The literature of rhythms in hematology is reviewed. Time-dependent variations in hematological variables have been extensively studied and rhythms have been described for all kinds of blood cells. Also the numbers of hemopoietic stem cells in the bone marrow undergo circadian variations. Our group has shown how such variations change with aging in mice. The relevance of time sequence studies in aging research of hemopoiesis was clearly demonstrated. In animal studies using cytometry, our group has demonstrated extensive circadian variations in cell cycle distribution of bone marrow cells, especially the DNA synthesis (S-phase). In humans a few and rather small time sequence studies of the bone marrow have been performed, so far. In this overview the clinical implications of circadian rhythms of S-phase variations measured by flow cytometry of human bone marrow cells are discussed. Male volunteers were examined every 4 h around-the-clock. The data indicated a lower proliferative activity during night, suggesting the possibility of reducing the bone marrow toxicity to cancer treatment when taking these time-dependent variations into consideration.