To investigate the activity of candidate regulatory molecules in embryogenesis, we have developed a general strategy for modifying and reporting resident chromosomal gene expression. The picornaviral internal ribosome-entry site was incorporated into gene targeting constructs to provide cap-independent translation of a selectable marker from fusion transcripts generated following homologous recombination. These promoterless constructs were highly efficient and have been used both to inactivate the stem-cellspecific transcription factor Oct-4 and to introduce a quantitative regulatory modification into the gene for a stem-cell maintenance factor, differentiation-inhibiting activity. In addition, the inclusion of a 3galactosidase reporter gene in the constructs enabled accurate and sensitive detection of cellular sites of transcription. This has allowed visualization of putative "stem-cell niches" in which sources of elevated expression of differentiation-inhibiting activity were localized to the differentiated cells surrounding colonies of stem cells.

The present study demonstrates increased endoglin expression in rats with severe hypertension and renal damage. This increased endoglin expression coincides with the period of higher renal damage and renal dysfunction.

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Endoglin is up-regulated in the post-ischaemic kidney and endoglin-haploinsufficient mice are protected from renal I-R injury. Endoglin may play a primary role in promoting inflammatory responses following renal I-R.

Survival signalling by ligand-activated tyrosine kinase receptors plays a crucial role in maintaining the balance between cell viability and apoptosis in multicellular organisms. To identify receptor domains and pathways involved in survival signalling, the nerve growth factor receptor TrkA was expressed in Rat-1/MycER TM ®broblasts. We demonstrate that wt-TrkA receptor delays c-Myc-, U.V.-and Cycloheximide-induced apoptosis and activates targets such as the mitogen-activated protein kinase (MAPK) Erk2 and the serine/threonine kinase Akt/PKB, both of which have been implicated in survival signalling. TrkA mutated within its SHC binding site (Y490F) delays c-Myc-induced apoptosis without activating endogenous Akt/PKB. In contrast, the TrkA Y490F mutant receptor does not delay U.V.-induced apoptosis whilst TrkA mutated at its PLC-g binding site (Y785F) is capable of protecting from apoptosis induced by c-Myc or U.V. treatment. The double mutant TrkA YY490/785FF fails to block either of these two apoptotic stimuli. While PI3-kinase inhibitors LY294002 and Wortmannin competely block survival signalling following U.V. treatment, neither drug a ects the ability of TrkA to block c-Myc-induced apoptosis. We show that the Akt/PKB pathway is essential for NGF stimulated TrkA survival signalling in the case of U.V.-induced apoptosis, but that apoptosis induced by c-Myc is also blocked by a novel, Akt/PKB-independent, pathway. These observations suggest that TrkA can activate di erent survival signalling pathways, which can interfere with speci®c apoptotic pathways.

Embryonic stem (ES) cells, derived from the inner cell mass of the preimplantation mouse embryo, are used increasingly as an experimental tool for the investigation of early mammalian development. The differentiation of these cells in vitro can be used as an assay for factors that regulate early developmental decisions in the embryo, while the effects of altered gene expression during early embryogenesis can be analyzed in chimeric mice generated from modified ES cells. The experimental versatility of ES cells would be significantly increased by the development of systems which allow precise control of heterologous gene expression. In this paper, we report that ES cells are responsive to alpha and beta interferons (IFNs). This property has been exploited for the development of inducible ES cell expression vectors, using the promoter of the human IFN-inducible gene, 6-16. The properties of these vectors have been analyzed in both transiently and stably transfected ES cells. Expression was minimal or absent in unstimulated ES cells, could be stimulated up to 100-fold by treatment of the cells with IFN, and increased in linear fashion with increasing levels of IFN. High levels of induced expression were maintained for extended periods of time in the continuous presence of the inducing signal or following a 12-h pulse with IFN. Treatment of ES cells with IFN did not affect their growth or differentiation in vitro or compromise their developmental potential. This combination of features makes the 6-16-based expression vectors suitable for the functional analysis of developmental control control genes in ES cells.

Chronic renal disease is characterized by the accumulation of extracellular matrix proteins in the kidney and a loss of renal function. Tubulointerstitial fibrosis has been reported to play an important role in the progression of chronic renal diseases. Transforming growth factor-beta1 (TGF-beta1) is a profibrotic cytokine playing a major contribution to fibrotic kidney disease. Endoglin is a membrane glycoprotein of the TGF-beta1 receptor system. The aim of this work was to determine the time-course expression of renal type I and IV collagens, endoglin and TGF-beta1 in a rat model of induced tubulointerstitial fibrosis at 1, 3, 10 and 17 days after unilateral ureteral obstruction (UUO). In 17 days-ligated (L)-renal samples, a marked interstitial fibrosis was detected by Masson's trichromic and Sirius red staining, accompanied by an increase in type I collagen expression as shown by immunohistochemical analysis. Northern blot studies revealed a progressive increase in collagen alpha2(I), TGF-beta1 and endoglin mRNA expression in L kidneys when compared with the corresponding non-ligated (NL) kidneys from the animals subjected to left UUO. Seventeen days after UUO, significant increases in collagen alpha2(I), collagen alpha1(IV), TGF-beta1 and endoglin mRNA levels were detected in L kidneys vs NL kidneys. Significantly higher levels of the protein endoglin were found in L kidneys than in NL kidneys 10 and 17 days following obstruction. A marked increase expression for endoglin and TGF-beta1 was localized in renal interstitium by immunohistochemical studies 17 days after obstruction. In conclusion, this work reports the upregulation of endoglin coincident to that of its ligand TGF-beta1 in the kidneys of rats with progressive tubulointerstitial fibrosis induced by UUO.

Aim Chronic kidney disease is characterized by tubulointerstitial fibrosis involving inflammation, tubular apoptosis, fibroblast proliferation and extracellular matrix accumulation. Cardiotrophin‐1, a member of the interleukin‐6 family of cytokines, protects several organs from damage by promoting survival and anti‐inflammatory effects. However, whether cardiotrophin‐1 participates in the response to chronic kidney injury leading to renal fibrosis is unknown. Methods We hypothesized and assessed the potential role of cardiotrophin‐1 in a mice model of tubulointerstitial fibrosis induced by unilateral ureteral obstruction (UUO). Results Three days after UUO, obstructed kidneys from cardiotrophin‐1−/− mice show higher expression of inflammatory markers IL‐1β, Cd68, ICAM‐1, COX‐2 and iNOs, higher activation of NF‐κB, higher amount of myofibroblasts and higher severity of tubular damage and apoptosis, compared with obstructed kidneys from wild‐type littermates. In a later stage, obstructed kidneys from cardiotrophin‐1−/− mice show higher fibrosis than obstructed kidneys from wild‐type mice. Interestingly, administration of exogenous cardiotrophin‐1 prevents the increased fibrosis resulting from the genetic knockout of cardiotrophin‐1 upon UUO, and supplementation of wild‐type mice with exogenous cardiotrophin‐1 further reduces the renal fibrosis induced by UUO. In vitro, renal myofibroblasts from cardiotrophin‐1−/− mice have higher collagen I and fibronectin expression and higher NF‐κB activation than wild‐type cells. Conclusions Cardiotrophin‐1 participates in the endogenous response that opposes renal damage by counteracting the inflammatory, apoptotic and fibrotic processes. And exogenous cardiotrophin‐1 is proposed as a candidate for the treatment and prevention of chronic renal fibrosis.