Expression of the Id family helix-loop-helix regulators during growth and development in the hematopoietic system

To better understand the molecular mechanism(s) by which growth and differentiation of the primitive hematopoietic stem cell is initiated, as well as the means by which the maturing cell can commit to development along a specific cell lineage, we elected to study the Id family of helix-loop-helix (HLH) transcriptional regulators. Some members of the HLH family are expressed in a stage-specific manner during hematopoietic development and can regulate the ability of immature hematopoietic cells to terminally differentiate. None of the four Id family genes were detected in the most primitive progenitors. Id-1 was widely expressed in proliferating bi- and unipotential progenitors, but its expression was downregulated in cells of increasing maturity; conversely, Id-2 and, to a limited extent, Id-3 gene expression increased as cells matured and lost proliferative capacity. Id-2 expression ran counter to that of Id-1 not only during maturation, but during periods of cell growth and arrest as well. This is quite distinct from the nonhematopoietic tissues, in which these two factors are coordinately expressed and suggests that Id-1 and Id-2 might be regulating very different events during hematopoiesis than they regulate in other cell types

Neurokinin-1 Receptor Signalling Impacts Bone Marrow Repopulation Efficiency

Tachykinins are a large group of neuropeptides with both central and peripheral activity. Despite the increasing number of studies reporting a growth supportive effect of tachykinin peptides in various in vitro stem cell systems, it remains unclear whether these findings are applicable in vivo. To determine how neurokinin-1 receptor (NK-1R) deficient hematopoietic stem cells would behave in a normal in vivo environment, we tested their reconstitution efficiency using competitive bone marrow repopulation assays. We show here that bone marrow taken from NK-1R deficient mice (Tacr1−/−) showed lineage specific B and T cell engraftment deficits compared to wild-type competitor bone marrow cells, providing evidence for an involvement of NK-1R signalling in adult hematopoiesis. Tachykinin knockout mice lacking the peptides SP and/or HK-1 (Tac1−/−, Tac4−/− and Tac1−/−/Tac4−/− mice) repopulated a lethally irradiated wild-type host with similar efficiency as competing wild-type bone marrow. The difference between peptide and receptor deficient mice indicates a paracrine and/or endocrine mechanism of action rather than autocrine signalling, as tachykinin peptides are supplied by the host environment

Unsuspected role of the brain morphogenetic gene Otx1 in hematopoiesis

Otx1 belongs to the paired class of homeobox genes and plays a pivotal role in brain development. Here, we show that Otx1 is expressed in hematopoietic pluripotent and erythroid progenitor cells. Moreover, bone marrow cells from mice lacking Otx1 exhibit a cell-autonomous impairment of the erythroid compartment. In agreement with these results, molecular analysis revealed decreased levels of erythroid genes that include the SCL and GATA-1 transcription factors. Accordingly, a gain of function of SCL rescues the erythroid deficiency in Otx1-/- mice. Taken together, our findings indicate a function for Otx1 in the regulation of blood cell production. There is growing evidence suggesting that common cellular and molecular mechanisms orchestrate differentiation in various tissues. Homeobox-containing genes seem to be strong candidate genes to regulate a number of developmental processes, including neurogenesis and hematopoiesis. Members of the Otx family (Otx1, Otx2, Otx3, and Crx) are the vertebrate homologues of the Drosophila head gap gene orthodenticle and encode transcription factors containing a bicoid-like homeodomain. They are temporally and spatially regulated during development and seem to be required for proper head and sense organ patterning. Otx1, Otx2, and Otx3 show partially overlapping, but distinct expression patterns, and Otx2, the first to be activated during development, plays a major role in gastrulation and in the early specification of the anterior neural plate. In contrast, Otx1 shows a later onset and is involved in corticogenesis, sense organ development, and pituitary function. Mice bearing targeted deletion of Otx1 are affected by a permanent epileptic phenotype and show multiple brain abnormalities and morphological defects of the acoustic and visual sense organs. In addition, at the prepubescent stage, they exhibit transient dwarfism and hypogonadism because of low levels of pituitary hormones. In the present study, we have investigated whether Otx1 also plays a role in blood cell production, as several homeobox genes of different families are involved in normal and/or malignant hematopoiesis

CDK6 levels regulate quiescence exit in human hematopoietic stem cells.

Regulated blood production is achieved through the hierarchical organization of dormant hematopoietic stem cell (HSC) subsets that differ in self-renewal potential and division frequency, with long-term (LT)-HSCs dividing the least. The molecular mechanisms underlying this variability in HSC division kinetics are unknown. We report here that quiescence exit kinetics are differentially regulated within human HSC subsets through the expression level of CDK6. LT-HSCs lack CDK6 protein. Short-term (ST)-HSCs are also quiescent but contain high CDK6 protein levels that permit rapid cell cycle entry upon mitogenic stimulation. Enforced CDK6 expression in LT-HSCs shortens quiescence exit and confers competitive advantage without impacting function. Computational modeling suggests that this independent control of quiescence exit kinetics inherently limits LT-HSC divisions and preserves the HSC pool to ensure lifelong hematopoiesis. Thus, differential expression of CDK6 underlies heterogeneity in stem cell quiescence states that functionally regulates this highly regenerative system.This work was supported by the Swiss National Science Foundation (E.L.), Roche (E.L.), the Fondation Suisse pour les Bourses en Me´ decine et Biologie (E.L.), the Swedish Research Council (S.Z.); and a Canadian Institutes of Health Research (CIHR) fellowship in partnership with the Aplastic Anemia and Myelodysplasia Association of Canada (S.Z.). Work in J.E.D.’s laboratory is supported by grants from the CIHR, Canadian Cancer Society, Terry Fox Foundation, Genome Canada through the Ontario Genomics Institute, Ontario Institute for Cancer Research with funds from the province of Ontario, a Canada Research Chair, the Princess Margaret Hospital foundation, and the Ontario Ministry of Health and Long Term Care (OMOHLTC). Research in E.L.’s laboratory is currently supported by a recruitment support from the Wellcome Trust and a core support grant from the Wellcome Trust and MRC to the Wellcome Trust – Medical Research Council Cambridge Stem Cell Institute.This is the final published version. It first appeared at http://www.cell.com/cell-stem-cell/abstract/S1934-5909%2815%2900018-1

Applicability of RNA standards for evaluating RT-qPCR assays and platforms

The availability of diverse RT-qPCR assay formats and technologies hinder comparability of data between platforms. Reference standards to facilitate platform evaluation and comparability are needed. We have explored using universal RNA standards for comparing the performance of a novel qPCR platform (Fluidigm® BioMark™) against the widely used ABI 7900HT system. Our results show that such standards may form part of a toolkit to evaluate the key performance characteristics of platforms

Accurate Expression Profiling of Very Small Cell Populations

BACKGROUND: Expression profiling, the measurement of all transcripts of a cell or tissue type, is currently the most comprehensive method to describe their physiological states. Given that accurate profiling methods currently available require RNA amounts found in thousands to millions of cells, many fields of biology working with specialized cell types cannot use these techniques because available cell numbers are limited. Currently available alternative methods for expression profiling from nanograms of RNA or from very small cell populations lack a broad validation of results to provide accurate information about the measured transcripts. METHODS AND FINDINGS: We provide evidence that currently available methods for expression profiling of very small cell populations are prone to technical noise and therefore cannot be used efficiently as discovery tools. Furthermore, we present Pico Profiling, a new expression profiling method from as few as ten cells, and we show that this approach is as informative as standard techniques from thousands to millions of cells. The central component of Pico Profiling is Whole Transcriptome Amplification (WTA), which generates expression profiles that are highly comparable to those produced by others, at different times, by standard protocols or by Real-time PCR. We provide a complete workflow from RNA isolation to analysis of expression profiles. CONCLUSIONS: Pico Profiling, as presented here, allows generating an accurate expression profile from cell populations as small as ten cells