Fetal liver cells produce both fetal and adult erythrocytes in semiallogeneic radiation chimeras: possible influence of adult environment

Two kinds of erythrocytes are released in the blood of irradiated adult hybrid mice grafted with parental fetal liver cells: fetal antigen- bearing erythrocytes (Ft+ cells) and adult-type Ft- erythrocytes. Both are of parental origin, as determined by immune lysis using histocompatibility alloantigens. The latter cells make up all the recipient's red blood cells 2 mo after receipt of the graft, Ft+ cells then being no longer detected. The transient duality of erythropoiesis in irradiated adults grafted with fetal liver cells has been confirmed by studying the kinetics of CFU-E populations, as characterized by their ability to give rise to Ft+ or Ft- erythrocytes. The results are discussed in terms of environmental factors that influenc erythroid differentiation.     

Does recombination improve selection on codon usage? Lessons from nematode and fly complete genomes

Understanding the factors responsible for variations in mutation patterns and selection efficacy along chromosomes is a prerequisite for deciphering genome sequences. Population genetics models predict a positive correlation between the efficacy of selection at a given locus and the local rate of recombination because of Hill-Robertson effects. Codon usage is considered one of the most striking examples that support this prediction at the molecular level. In a wide range of species including Caenorhabditis elegans and Drosophila melanogaster, codon usage is essentially shaped by selection acting for translational efficiency. Codon usage bias correlates positively with recombination rate in Drosophila, apparently supporting the hypothesis that selection on codon usage is improved by recombination. Here we present an exhaustive analysis of codon usage in C. elegans and D. melanogaster complete genomes. We show that in both genomes there is a positive correlation between recombination rate and the frequency of optimal codons. However, we demonstrate that in both species, this effect is due to a mutational bias toward G and C bases in regions of high recombination rate, possibly as a direct consequence of the recombination process. The correlation between codon usage bias and recombination rate in these species appears to be essentially determined by recombination-dependent mutational patterns, rather than selective effects. This result highlights that it is necessary to take into account the mutagenic effect of recombination to understand the evolutionary role and impact of recombination.     

Erythroid colony formation by human CFU-E is stimulated by compatible human serum but impaired by blood group antibodies

Normal human serum was shown to stimulate the proliferation of human CFU-E when added into in vitro cultures of bone marrow cells. However, this was observed only when donors of serum and bone marrow cells were compatible on the basis of their blood groups. Absorption of incompatible sera removed the inhibition. Monoclonal anti-blood group antibodies exhibited the same pattern of CFU-E inhibition. The inhibition was complement-independent. Using suspension bone marrow cultures, it was shown that this blockage took place at an earlier differentiation step than the CFU-E level. This effect should be taken into account in studies of the inhibiting activities present in human anaemic sera.     

Immunochemical properties of antigens present on immature erythrocytes from mouse and rat

Summary Rabbit antisera directed against erythrocytes from anemic mice or from newborn rats, once absorbed on homologous normal adult erythrocytes, recognize antigens present respectively on immature erythrocytes from anemic adult mice or rats (Im M and Im R antigens). Using iodinated immature erythrocytes from both species, homologous sera precipitated two populations of antigens showing 230,000 D and 95,000 D molecular weights. Im M antigens (230,000 and 95,000 D) were partially precipitated using anti-Im R serum. After total absorption of the sample by anti-Im R serum, both 230,000 and 95,000 D antigens were still immunoprecipitated using anti-Im M serum. Similar results were obtained using Im R antigens and anti-Im M serum then anti-Im R serum. This demonstrates that some Im specificities are common to rat and mouse while others, showing identical molecular weights, are species-specific.     

Expression of human colony-stimulating factor-1 (CSF-1) receptor in murine pluripotent hematopoietic NFS-60 cells induces long-term proliferation in response to CSF-1 without loss of erythroid differentiation potential

NFS-60 and FDCP-Mix cells are interleukin-3--dependent multipotent hematopoietic cells that can differentiate in vitro into mature myeloid and erythroid cells. Retrovirus-mediated transfer of the human colony- stimulating factor-1 (CSF-1) receptor gene (c-fms) enabled NFS-60 cells but not FDCP-Mix cells to proliferate in response to CSF-1. The phenotype of NFS-60 cells expressing the human CSF-1 receptor (CSF-1R) grown in CSF-1 did not grossly differ from that of original NFS-60 as assessed by cytochemical and surface markers. Importantly, these cells retained their erythroid potentiality. In contrast, a CSF-1-dependent variant of NFS-60, strongly expressing murine CSF-1R, differentiated into monocyte/macrophages upon CSF-1 stimulation and almost totally lost its erythroid potentiality. We also observed that NFS-60 but not FDCP-Mix cells could grow in response to stem cell factor, (SCF), although both cell lines express relatively high amounts of SCF receptors. This suggests that SCF-R and CSF-1R signalling pathways share at least one component that may be missing or insufficiently expressed in FDCP-Mix cells. Taken together, these results suggest that human CSF-1R can use the SCF-R signalling pathway in murine multipotent cells and thereby favor self-renewal versus differentiation.