Background and aims: BCS1L is a chaperone assembling the Rieske iron-sulphur protein into respiratory chain complex III. To study BCS1L functions and pathophysiology of GRACILE syndrome (MIM 603358), we have introduced the disease mutation (Bcs1l 232A> G) into mice, using gene targeting. The homozygous mutant mice (Bcs1lG/G) exhibit a lethal disease after 24 d of age resembling GRACILE syndrome: growth restriction, hepatopathy, tubulopathy, and progressive complex III deficiency. We aimed to assess metabolic changes in liver of Bcs1lG/G mice to characterize genotype-metabolomic phenotype correlation. Methods: Bcs1lG/G mice and littermate controls were sacrificed at age 7 (14 pairs) and 24 d (symptomless, 8 pairs), and 5±1 wk (affected, 18 pairs). Snap-frozen liver samples were stored in 80°C. Metabolomic analyses of 199 metabolites (amino acids, series of carnitines and lipids, HODE, HETE, bile acids, metabolites of the energy metabolism) were carried out at BIOCRATES Life Sciences AG. Results: Profound changes in liver metabolite levels (increase in medium and long chain acylcarnitines and decrease in short chain acylcarnitines) were found in 5±1 wk, and slight changes in 24d Bcs1lG/G animals. Markers of oxidative stress (15S-HETE, 12S-HETE, 13-HODE and methioninsulfoxide), bile acids, amino acids, biogenic amino acids, sphingolipids and phosphatidylcholines were significantly increased in affected Bcs1lG/G animals only. Hexose-phosphate, lactate, alpha – ketoglurate were decreased compared to littermates Conclusions: Affected Bcs1lG/G mice with progressive complex III deficiency have major changes in acylcarnitine metabolism, which seems to precede oxidative stress and profound changes in metabolites indicating cell injury as well as liver dysfunction.

Specific inactivation of TGFbeta signaling in neural crest stem cells (NCSCs) results in cardiovascular defects and thymic, parathyroid, and craniofacial anomalies. All these malformations characterize DiGeorge syndrome, the most common microdeletion syndrome in humans. Consistent with a role of TGFbeta in promoting non-neural lineages in NCSCs, mutant neural crest cells migrate into the pharyngeal apparatus but are unable to acquire non-neural cell fates. Moreover, in neural crest cells, TGFbeta signaling is both sufficient and required for phosphorylation of CrkL, a signal adaptor protein implicated in the development of DiGeorge syndrome. Thus, TGFbeta signal modulation in neural crest differentiation might play a crucial role in the etiology of DiGeorge syndrome.

We have taken advantage of the Cre/lox system to generate a mouse model with inducible deficiency of transforming growth factor beta receptor II (TbetaRII). Using this approach, transforming growth factor beta (TGF-beta) signaling deficiency can be restricted to the hematopoietic system by bone marrow transplantation. Mice that received transplants with TbetaRII-/- bone marrow develop a lethal inflammatory disorder closely resembling that of TGF-beta1-null mice. Previous in vitro studies have suggested multiple roles for TGF-beta in T-cell development, including proliferation, apoptosis, and differentiation. We used our transplantation model to ask whether T-cell development is normal in the absence of TGF-beta signaling. The findings show for the first time in vivo and in fetal thymus organ culture (FTOC) that TGF-beta is not required for thymocytes to differentiate along the entire pathway of thymic T-cell development, as defined by the expression patterns of CD4, CD8, CD25, and CD44. In contrast to previous investigations, no increase of thymocyte apoptosis was observed. However, TbetaRII-deficient CD8+ thymocytes displayed a 2-fold increase in proliferation rate, as determined by bromodeoxyuridine (BrdU) incorporation in vivo. These results reinforce the importance of TGF-beta as an immune regulator critical for T-cell function.

Enforced expression of Hoxb4 dramatically increases the regeneration of murine hematopoietic stem cells (HSCs) after transplantation and enhances the repopulation ability of human severe combined immunodeficiency (SCID) repopulating cells. Therefore, we asked what physiologic role Hoxb4 has in hematopoiesis. A novel mouse model lacking the entire Hoxb4 gene exhibits significantly reduced cellularity in spleen and bone marrow (BM) and a subtle reduction in red blood cell counts and hemoglobin values. A mild reduction was observed in the numbers of primitive progenitors and stem cells in adult BM and fetal liver, whereas lineage distribution was normal. Although the cell cycle kinetics of primitive progenitors was normal during endogenous hematopoiesis, defects in proliferative responses of BM Lin(-) Sca1(+) c-kit(+) stem and progenitor cells were observed in culture and in vivo after the transplantation of BM and fetal liver HSCs. Quantitative analysis of mRNA from fetal liver revealed that a deficiency of Hoxb4 alone changed the expression levels of several other Hox genes and of genes involved in cell cycle regulation. In summary, the deficiency of Hoxb4 leads to hypocellularity in hematopoietic organs and impaired proliferative capacity. However, Hoxb4 is not required for the generation of HSCs or the maintenance of steady state hematopoiesis.

Transforming growth factor beta (TGF-beta) is a potent inhibitor of hepatocyte proliferation in vitro and is suggested to be a key negative regulator of liver growth. To directly address the role of TGF-beta signaling in liver regeneration in vivo, the TGF-beta type II receptor gene (Tgfbr2) was selectively deleted in hepatocytes by crossing "floxed" Tgfbr2 conditional knockout mice with transgenic mice expressing Cre under control of the albumin promoter. Hepatocytes isolated from liver-specific Tgfbr2 knockout (R2LivKO) mice were refractory to the growth inhibitory effects of TGF-beta1. The peak of DNA synthesis after 70% partial hepatectomy occurred earlier (36 vs. 48 hours) and was 1.7-fold higher in R2LivKO mice compared with controls. Accelerated S-phase entry by proliferating R2LivKO hepatocytes coincided with the hyperphosphorylation of Rb protein and the early upregulation of cyclin D1 and cyclin E. However, by 120 hours after partial hepatectomy, hepatocyte proliferation was back to baseline in both control and R2LivKO liver. Regenerating R2LivKO liver showed evidence of increased signaling by activin A and persistent activity of the Smad pathway. Blockage of activin A signaling by the specific inhibitor follistatin resulted in increased hepatocyte proliferation at 120 hours, particularly in R2LivKO livers. In conclusion, TGF-beta regulates G(1) to S phase transition of hepatocytes, but intact signaling by TGF-beta is not required for termination of liver regeneration. Increased signaling by activin A may compensate to regulate liver regeneration when signaling through the TGF-beta pathway is abolished, and may be a principal factor in the termination of liver regeneration.

Studies in vitro implicate transforming growth factor beta (TGF-beta) as a key regulator of hematopoiesis with potent inhibitory effects on progenitor and stem cell proliferation. In vivo studies have been hampered by early lethality of knock-out mice for TGF-beta isoforms and the receptors. To directly assess the role of TGF-beta signaling for hematopoiesis and hematopoietic stem cell (HSC) function in vivo, we generated a conditional knock-out model in which a disruption of the TGF-beta type I receptor (T beta RI) gene was induced in adult mice. HSCs from induced mice showed increased proliferation recruitment when cultured as single cells under low stimulatory conditions in vitro, consistent with an inhibitory role of TGF-beta in HSC proliferation. However, induced T beta RI null mice show normal in vivo hematopoiesis with normal numbers and differentiation ability of hematopoietic progenitor cells. Furthermore HSCs from T beta RI null mice exhibit a normal cell cycle distribution and do not differ in their ability long term to repopulate primary and secondary recipient mice following bone marrow transplantation. These findings challenge the classical view that TGF-beta is an essential negative regulator of hematopoietic stem cells under physiologic conditions in vivo.

Recent studies in mouse models deficient in transforming growth factor beta (TGF-beta) signaling have documented TGF-beta as one of the major regulators of immune function. TGF-beta1-null animals demonstrated massive autoimmune inflammation affecting multiple organs, but attempts to transfer the phenotype to normal animals by bone marrow transplantation only resulted in minor inflammatory lesions. We wanted to ask whether a lethal inflammatory phenotype would develop following transplantation of bone marrow deficient for the TGF-beta type II receptor (TbetaRII) gene to normal recipient animals. The TbetaRII-null mutation would generate a cell autonomous phenotype that cannot be reverted by the influence of endocrine or paracrine TGF-beta derived from the recipient animal. We have generated conditional knockout mice in which the TbetaRII gene is disrupted upon induction with interferon-alphabeta or polyI:polyC. We show that induction of TbetaRII gene disruption in these mice by polyI:polyC results in a lethal inflammatory disease. Importantly, bone marrow from conditional knockout mice transferred to normal recipent mice caused a similar lethal inflammation, regardless of whether induction of TGF-beta receptor deficiency occurred in donor animals before, or in recipient animals after transplantation. These results show that TGF-beta signaling deficiency within cells of hematopoietic origin is sufficient to cause a lethal inflammatory disorder in mice. This animal model provides an important tool to further clarify the pathogenic mechanisms in animals deficient for TGF-beta signaling and the importance of TGF-beta to regulate immune functions.

Deletion of the transforming growth factor β1 (TGF‐β1) gene in mice has previously suggested that it regulates both hematopoiesis and angiogenesis. To define the function of TGF‐β more precisely, we inactivated the TGF‐β type I receptor (TβRI) gene by gene targeting. Mice lacking TβRI 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 TβRI−/− yolk sacs, clonogenic assays on yolk sac‐derived hematopoietic precursors in vitro revealed that TβRI−/− mice exhibit normal hematopoietic potential compared with wild‐type and heterozygous siblings. Endothelial cells derived from TβRI‐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 TβRI is crucial for the function of TGF‐β 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‐β signaling via TβRI.