Summary Maintenance of a hematopoietic progenitor population requires extensive interaction with cells within a microenvironment or niche. In the Drosophila hematopoietic organ, niche-derived Hedgehog signaling maintains the progenitor population. Here we show that the hematopoietic progenitors also require a signal mediated by Adenosine deaminase growth factor A (Adgf-A) arising from differentiating cells that regulates extracellular levels of adenosine. The adenosine signal opposes the effects of Hedgehog signaling within the hematopoietic progenitor cells and the magnitude of the adenosine signal is kept in check by the level of Adgf-A secreted from differentiating cells. Our findings reveal signals arising from differentiating cells that are required for maintaining progenitor cell quiescence, and that function with the niche-derived signal in maintaining the progenitor state. Similar homeostatic mechanisms are likely to be utilized in other systems that maintain relatively large numbers of progenitors that are not all in direct contact with the cells of the niche.

SUMMARY Drosophila hematopoietic progenitor maintenance involves both near neighbor and systemic interactions. This study shows that olfactory receptor neurons (ORNs) function upstream of a small set of neurosecretory cells that express GABA. Upon olfactory stimulation, GABA from these neurosecretory cells is secreted into the circulating hemolymph and binds to metabotropic GABAB receptors expressed on blood progenitors within the hematopoietic organ, the lymph gland. The resulting GABA signal causes high cytosolic Ca2+, necessary and sufficient for progenitor maintenance. Thus the activation of an odorant receptor is essential for blood progenitor maintenance and consequently, larvae raised on minimal odor environments fail to sustain a pool of hematopoietic progenitors. This study links sensory perception and the effects of its deprivation on the integrity of the hematopoietic and innate immune systems in Drosophila.

Blood progenitors within the lymph gland, a larval organ that supports hematopoiesis in Drosophila melanogaster, are maintained by integrating signals emanating from niche-like cells and those from differentiating blood cells. We term the signal from differentiating cells the ‘equilibrium signal’ in order to distinguish it from the ‘niche signal’. Earlier we showed that equilibrium signaling utilizes Pvr (the Drosophila PDGF/VEGF receptor), STAT92E, and adenosine deaminase-related growth factor A (ADGF-A) (Mondal et al., 2011). Little is known about how this signal initiates during hematopoietic development. To identify new genes involved in lymph gland blood progenitor maintenance, particularly those involved in equilibrium signaling, we performed a genetic screen that identified bip1 (bric à brac interacting protein 1) and Nucleoporin 98 (Nup98) as additional regulators of the equilibrium signal. We show that the products of these genes along with the Bip1-interacting protein RpS8 (Ribosomal protein S8) are required for the proper expression of Pvr.DOI: http://dx.doi.org/10.7554/eLife.03626.001

The senegal haplotype and the polymorphism at -158 of G(gamma) was linked to the high-HbF phenotype.

Molecular breakpoint of the BCR-ABL fusion gene has been characterized for 122 chronic myeloid leukemia patients. Out of 122 cases, 33 b2a2, 69 b3a2, 2 e1a2, and 2 e19a2 cases have been detected. Six coexpressed both b2a2 and b3a2 transcripts. All the coexpressing samples had an A>G polymorphism at the putative splice branchpoint in intron 13. The T>C polymorphism in exon 13, reported to be linked to coexpression, was not present in all the coexpressing patients. No correlation of transcript type with platelet count was detected. Those expressing b2a2 transcript were diagnosed at relatively younger age and with higher white blood cell count, in agreement with other reports. However, the correlation was not statistically significant. Am. J. Hematol. 81:845-849, 2006. V V C 2006 Wiley-Liss, Inc.