crm-1 facilitates BMP signaling to control body size in Caenorhabditis elegans

We have identified in Caenorhabditis elegans a homologue of the vertebrate Crim1, crm-1, which encodes a putative transmembrane protein with multiple cysteine-rich (CR) domains known to have bone morphogenetic proteins (BMPs) binding activity. Using the body morphology of C. elegans as an indicator, we showed that attenuation of crm-1 activity leads to a small body phenotype reminiscent of that of BMP pathway mutants. We showed that the crm-1 loss-of-function phenotype can be rescued by constitutive supply of sma-4 activity. crm-1 can enhance BMP signaling and this activity is dependent on the presence of the DBL-1 ligand and its receptors. crm-1 is expressed in neurons at the ventral nerve cord, where the DBL-1 ligand is produced. However, ectopic expression experiments reveal that crm-1 gene products act outside the DBL-1 producing cells and function non-autonomously to facilitate dbl/sma pathway signaling to control body size.     

Nrg1 functions as a global transcriptional repressor of glucose-repressed genes through its direct binding to the specific promoter regions

Nrg1 is a zinc finger protein involved in the glucose repression of several glucose-repressed genes such as STA1, SUC2, and GAL1. Although the molecular details of the Nrg1-mediated repression of STA1 have been partly characterized, it still remains largely unknown how Nrg1 regulates these multiple target genes. In this study, we show that Nrg1 mediates the glucose repression of SUC2 and HXT2 through its direct binding to the specific promoter regions; it binds to the −404 to −360 region of the SUC2 promoter and the −957 to −810 region of the HXT2 promoter. Nrg1 also interacts with the −380 to −250 region of the PCK1 promoter, suggesting that it might also contribute to the PCK1 repression. In addition, ChIP assays confirmed that Nrg1 associated with specific promoter regions of these glucose-repressed genes in vivo. Analysis of the DNA fragments to which it binds indicates that Nrg1 may recognize T/ACCCC sequence within the promoters of these glucose-repressed genes as well as in its own promoter. Collectively, our findings indicate that Nrg1 mediates the glucose repression of multiple genes through its direct binding to the specific promoter regions.     

Sox3 expression is maintained by FGF signaling and restricted to the neural plate by Vent proteins in the Xenopus embryo

The formation of the nervous system is initiated when ectodermal cells adopt the neural fate. Studies in Xenopus demonstrate that inhibition of BMP results in the formation of neural tissue. However, the molecular mechanism driving the expression of early neural genes in response to this inhibition is unknown. Moreover, controversy remains regarding the sufficiency of BMP inhibition for neural induction. To address these questions, we performed a detailed analysis of the regulation of the soxB1 gene, sox3, one of the earliest genes expressed in the neuroectoderm. Using ectodermal explant assays, we analyzed the role of BMP, Wnt and FGF signaling in the regulation of sox3 and the closely related soxB1 gene, sox2. Our results demonstrate that both sox3 and sox2 are induced in response to BMP antagonism, but by distinct mechanisms and that the activation of both genes is independent of FGF signaling. However, both require FGF for the maintenance of their expression. Finally, sox3 genomic elements were identified and characterized and an element required for BMP-mediated repression via Vent proteins was identified through the use of transgenesis and computational analysis. Interestingly, none of the elements required for sox3 expression were identified in the sox2 locus. Together our data indicate that two closely related genes have unique mechanisms of gene regulation at the onset of neural development.     

Complex interactions between bovine plasminogen and streptococcal plasminogen activator PauA

The interactions between bovine plasminogen and the streptococcal plasminogen activator PauA that culminate in the generation of plasmin are not fully understood. Formation of an equimolar activation complex comprising PauA and plasminogen by non-proteolytic means is a prerequisite to the recruitment of substrate plasminogen; however the determinants that facilitate these interactions have yet to be defined. A mutagenesis strategy comprising nested deletions and random point substitutions indicated roles for both amino and carboxyl-terminal regions of PauA and identified further essential residues within the alpha domain of the plasminogen activator. A critical region within the alpha domain was identified using non-overlapping PauA peptides to block the interaction between PauA and bovine plasminogen, preventing formation of the activation complex. Homology modelling of the activation complex based upon the known structures of streptokinase complexed with human plasmin supported these findings by placing critical residues in close proximity to the plasmin component of the activation complex.     

Downregulation of microRNA-214 and overexpression of FGFR-1 contribute to hepatocellular carcinoma metastasis

miR-214 is one of the most significantly downregulated microRNAs (miRNAs) in hepatocellular carcinoma (HCC). Fibroblast growth factor receptor 1 (FGFR-1) is a miR-214 target gene implicated in the progression of HCC. However, the roles of miR-214 and FGFR-1 in HCC are not fully understood. Here, we analyzed the expression of miR-214 and FGFR-1 in 65 cases of HCC and paired non-neoplastic tissue specimens using real-time PCR and Western blot (WB), respectively. Our data indicated that miR-214 was downregulated and FGFR-1 was overexpressed in HCC compared to the paired non-neoplastic tissues. The low miR-214 expression was correlated with portal vein invasion (p = 0.016) and early recurrence (p = 0.045) in HCC patients. Moreover, the low miR-214 expression was correlated with high positive rate of FGFR-1 in HCC cases (p = 0.020). Our data further demonstrated that miR-214 overexpression in SK-HEP1 and HepG2 cells downregulated FGFR-1 expression and inhibited liver cancer cell invasion. The Luciferase assay results further demonstrated the targeted regulation of FGFR-1 by miR-214. In conclusion, our data indicate that the downregulation of miR-214 in HCC and the upregulation of its target gene FGFR-1 is associated with HCC progression. Therefore, miR-214 and FGFR-1 are potential prognostic markers and therapeutic targets in HCC.     

Analysis of the molecular cascade responsible for mesodermal limb chondrogenesis: Sox genes and BMP signaling

Here, we have studied how Sox genes and BMP signaling are functionally coupled during limb chondrogenesis. Using the experimental model of TGFbeta1-induced interdigital digits, we dissect the sequence of morphological and molecular events during in vivo chondrogenesis. Our results show that Sox8 and Sox9 are the most precocious markers of limb cartilage, and their induction is independent and precedes the activation of BMP signaling. Sox10 appears also to cooperate with Sox9 and Sox8 in the establishment of the digit cartilages. In addition, we show that experimental induction of Sox gene expression in the interdigital mesoderm is accompanied by loss of the apoptotic response to exogenous BMPs. L-Sox5 and Sox6 are respectively induced coincident and after the expression of Bmpr1b in the prechondrogenic aggregate, and their activation correlates with the induction of Type II Collagen and Aggrecan genes in the differentiating cartilages. The expression of Bmpr1b precedes the appearance of morphological changes in the prechondrogenic aggregate and establishes a landmark from which the maintenance of the expression of all Sox genes and the progress of cartilage differentiation becomes dependent on BMPs. Moreover, we show that Ventroptin precedes Noggin in the modulation of BMP activity in the developing cartilages. In summary, our findings suggest that Sox8, Sox9, and Sox10 have a cooperative function conferring chondrogenic competence to limb mesoderm in response to BMP signals. In turn, BMPs in concert with Sox9, Sox6, and L-Sox5 would be responsible for the execution and maintenance of the cartilage differentiation program.