Developmental changes in the pattern of larval beta-globin gene expression in Xenopus laevis. Identification of two early larval beta-globin mRNA sequences

We have analysed beta-globin mRNA sequences in total RNA extracted from embryos and tadpoles of Xenopus laevis at different stages of development and we have identified the most abundantly transcribed beta-globin mRNA (beta T1). The entire nucleotide sequence of a cDNA clone corresponding to this mRNA is known. We have now identified the gene corresponding to this mRNA and we have determined the nucleotide sequences of its immediate 5'-flanking region. Using a DNA fragment from within the coding region of the cloned beta T1 cDNA we show, by primer extension analysis, that beta T1 mRNA is first detectable at stage 28-32 of development. This is the time at which the first presumptive erythropoietic tissue, the ventral blood island, becomes observable histologically. We show that two minor beta-globin genes, distinct from beta T1, are expressed during early stages of development, and that their expression ceases shortly after the beginning of the feeding stage. We term these two early larval genes beta E1 and beta E2. A third minor beta-globin gene is expressed during early development but, unlike beta E1 and beta E2, it is also expressed throughout subsequent larval development. We term this gene beta T2 and show that it corresponds to a gene previously termed beta LII. Finally, using a primer derived from the major adult beta-globin gene (beta 1), we have analysed the accumulation of the major adult beta-globin mRNA during larval development, and we show that this sequence does not accumulate to any significant level before metamorphosis.     

Dual effect of chemokine CCL7/MCP-3 in the development of renal tubulointerstitial fibrosis

Most end-stage renal disease kidneys display accumulation of extracellular matrix (ECM) in the renal tubular compartment (tubular interstitial fibrosis – TIF) which is strongly correlated with the future loss of renal function. Although inflammation is a key event in the development of TIF, it can also have a beneficial anti-fibrotic role depending in particular on the stage of the pathology. Chemokines play an important role in monocyte extravasation in the inflammatory process. CCL2 has already been shown to be involved in the development of TIF but CCL7, a close relative of CCL2 and able to bind to similar receptors, has not been studied in renal disease. We therefore studied chemokine CCL7 in a model of unilateral ureteral obstruction (UUO)-induced TIF. We observed that the role of CCL7 differs depending on the stage of the pathology. In early stages (0–8 days), CCL7 deficient (CCL7-KO) mice displayed attenuated TIF potentially involving two mechanisms: an early (0–3 days) decrease of inflammatory cell infiltration followed (3–8 days) by a decrease in tubular ECM production independent of inflammation. In contrast, during later stages of obstruction (10–14 days), CCL7-KO mice displayed increased TIF which was again associated with reduced inflammation. Interestingly, the switch between this anti- to profibrotic effect was accompanied by an increased influx of immunosuppressive regulatory T cells. In conclusion, these results highlight for the first time a dual role for CCL7 in the development of renal TIF, deleterious in early stages but beneficial during later stages.