Abnormal angiogenesis but intact hematopoietic potential in TGF-beta type I receptor-deficient mice

Abstract

Deletion of the transforming growth factor beta1 (TGF-beta1) gene in mice has previously suggested that it regulates both hematopoiesis and angiogenesis. To define the function of TGF-beta more precisely, we inactivated the TGF-beta type I receptor (TbetaRI) gene by gene targeting. Mice lacking TbetaRI die at midgestation, exhibiting severe defects in vascular development of the yolk sac and placenta, and an absence of circulating red blood cells. However, despite obvious anemia in the TbetaRI(-/-) yolk sacs, clonogenic assays on yolk sac-derived hematopoietic precursors in vitro revealed that TbetaRI(-/-) mice exhibit normal hematopoietic potential compared with wild-type and heterozygous siblings. Endothelial cells derived from TbetaRI-deficient embryos show enhanced cell proliferation, improper migratory behavior and impaired fibronectin production in vitro, defects that are associated with the vascular defects seen in vivo. We thus demonstrate here that, while TbetaRI is crucial for the function of TGF-beta during vascular development and can not be compensated for by the activin receptor-like kinase-1 (ALK-1), functional hematopoiesis and development of hematopoietic progenitors is not dependent on TGF-beta signaling via TbetaRI.

Neuron-specific TGF-β signaling deficiency results in retinal detachment and cataracts in mice

“…The lack of significant effects on the retina in TGF-β1 and-β3 knockout mice is likely due to the compensatory effects of the other TGF-β isoforms. No conclusive results were obtained with TGF-β RI and RII knockout mice because of embryonic lethality at E10.5 [7,9]. Consistent retinal detachment, at the RPE/photoreceptor layer junction has been reported in TGF-β2 and-β3 double-deficient mice, which exhibit embryonic lethality at E15.5 [17].…”

“…Generation and characterization of TGF-β RI floxed (TGF-β RI f/f ) mice (C57Bl/6 X 129SvJ strain) were previously reported [9]. NestinCre mice were crossed with the TGF-β RI f/f mice to generate Nestin-Cre;TGF-β RI f/+ .…”

“…PCR analysis for the Cre gene and TGF-β RI floxed alleles were carried out as described [9,16]. Cre expression was analyzed by determining LacZ activity using a standard staining protocol as described [16].…”

“…The key roles of TGF-β and its receptors in retinal fibrosis in proliferative retinal disorders and in macular degeneration are well documented (8). In mammals there are three isoforms of TGF-β designated as TGF-β 1, 2, and 3, with many overlapping physiological functions and some distinct developmental roles [7,9,10]. TGF-β is generally secreted by the cells in an inactive (latent) form, that has to be activated by proteolytic cleavage.…”

“…Since nestin is expressed in retinal neuronal cells from embryonic day (E) 12.5 [13], the Cre enzyme should be active from that time in nestin-Cre mice. Expression of TGF-β RI in the retina starts at E14 [9,14]. Thus, our strategy should render TGF-β RI nonfunctional in retinal cells just before its expression starts in the cKO mice.…”