BMPs induce dermal markers and ectopic feather tracts

Bone morphogenetic protein (BMP) signaling is known to be involved in multiple inductive events during embryogenesis including the development of amniote skin. Here, we demonstrate that early application of BMP-2 to the lateral trunk of chick embryos induces the formation of dense dermis, which is competent to participate in feather development. We show that BMPs induce the dermis markers Msx-1 and cDermo-1 and lead to dermal proliferation, to expression of β-catenin, and eventually to the formation of ectopic feather tracts in originally featherless regions of chick skin. Moreover, we present a detailed analysis of cDermo-1 expression during early feather development. The data implicate that cDermo-1 is located downstream of BMP in a signaling pathway that leads to condensation of dermal cells. The roles of BMP and cDermo-1 during development of dermis and feather primordia are discussed.     

TT2, TT8, and TTG1 synergistically specify the expression of BANYULS and proanthocyanidin biosynthesis in Arabidopsis thaliana

Genetic analyses have demonstrated that together with TTG1, a WD-repeat (WDR) protein, TT2 (MYB), and TT8 (bHLH) are necessary for the correct expression of BANYULS (BAN). This gene codes for the core enzyme of proanthocyanidin biosynthesis in Arabidopsis thaliana seed coat. The interplays of TT2, TT8, and their closest MYB/bHLH relatives, with TTG1 and the BAN promoter have been investigated using a combination of genetic and molecular approaches, both in yeast and in planta. The results obtained using glucocorticoid receptor fusion proteins in planta strongly suggest that TT2, TT8, and TTG1 can directly activate BAN expression. Experiments using yeast two- and three-hybrid clearly demonstrated that TT2, TT8, and TTG1 can form a stable ternary complex. Furthermore, although TT2 and TT8 were able to bind to the BAN promoter when simultaneously expressed in yeast, the activity of the complex correlated with the level of TTG1 expression in A. thaliana protoplasts. In addition, transient expression experiments revealed that TTG1 acts mainly through the bHLH partner (i.e. TT8 or related proteins) and that TT2 cannot be replaced by any other related A. thaliana MYB proteins to activate BAN. Finally and consistent with these results, the ectopic expression of TT2 was sufficient to trigger BAN activation in vegetative parts, but only where TTG1 was expressed. Taken together, these results indicate that TT2, TT8, and TTG1 can form a ternary complex directly regulating BAN expression in planta.     

Load application induces changes in the expression levels of Sox-9, FGFR-3 and VEGF in condylar chondrocytes

Experimental and clinical observations have proven the modulatory effects of mechanical loading on the development and maintenance of cartilage architecture. Here we examined the involvement of Sox-9, FGFR-3 and VEGF (pivotal factors controlling cartilage development and growth) in the mechano-transduction pathway of mandibular condylar cartilage by changing the dynamics of the transmitted load via changes in food hardness. To this end, condyle cartilage tissue of rats fed with hard or soft food was analyzed immunohistochemically at various time points. Our findings demonstrate that different mechanical loading conditions in condylar chondrocytes trigger differentiation-/maturation-related processes by affecting the expression levels of these factors, ultimately influencing condylar cartilage growth.     

TT8 controls its own expression in a feedback regulation involving TTG1 and homologous MYB and bHLH factors, allowing a strong and cell-specific accumulation of flavonoids in Arabidopsis thaliana

The control of TT8 expression was investigated in this study, and it was demonstrated that it constitutes a major regulatory step in the specific activation of the expression of flavonoid structural genes. First, the GUS activity generated in planta from a TT8::uidA construct revealed cell-specific activation of the TT8 promoter consistent with the known involvement of the TT8 bHLH factor in proanthocyanidin, anthocyanin and mucilage biosynthesis. Moreover, the activity of this reporter construct was strongly affected in ttg1, TT2 overexpressers (OE), and PAP1-OE, suggesting interplay between TT2, PAP1, TTG1 and the activation of the TT8 promoter in planta. To further investigate the mechanisms involved, we used 35S::TT2-GR and 35S::TTG1-GR transgenic plants (expressing fusion proteins with the glucocorticoid receptor), as well as one-hybrid experiments, to determine the direct effect of these factors on TT8 expression. Interestingly, in vivo binding of TT2 and PAP1 to the TT8 promoter was dependent on the simultaneous expression of TT8 or the homologous bHLH factors GL3 and EGL3. Consistent with these results, the activity of the TT8::uidA reporter was strongly affected in the seed endothelium of a tt8 mutant. Similarly, a strong decrease in the level of TT8 mRNA was detected in the siliques of a gl3 x egl3 mutant and in plants that express a dominant negative form of the PAP1 protein, suggesting that TT8 expression is controlled by different combinations of MYB and bHLH factors in planta. The importance of this positive feedback mechanism in the strong and specific induction of proanthocyanidin biosynthesis in the seed coat of Arabidopsis thaliana is discussed.     

Dorsal dermis development depends on a signal from the dorsal neural tube, which can be substituted by Wnt-1

To investigate the origin and nature of the signals responsible for specification of the dermatomal lineage, excised axial organs in 2-day-old chick embryos were replaced by grafts of the dorsal neural tube, or the ventral neural tube plus the notochord, or aggregates of cells engineered to produce Sonic hedgehog (Shh), Noggin, BMP-2, Wnt-1, or Wnt-3a. By E10, grafts of the ventral neural tube plus notochord or of cells producing Shh led to differentiation of cartilage and muscles, and an impaired dermis derived from already segmented somites. In contrast, grafts of the dorsal neural tube, or of cells producing Wnt-1, triggered the formation of a feather-inducing dermis. These results show that the dermatome inducer is produced by the dorsal neural tube. The signal can be Wnt-1 itself, or can be mediated, or at least mimicked by Wnt-1.     

Genetic analysis of the TBX1 gene promoter in indirect inguinal hernia

Inguinal hernia is a common disease, most cases of which are indirect inguinal hernia (IIH). Genetic factors play an important role for inguinal hernia. Increased incidences of inguinal hernia have been reported in patients with 22q11.2 microdeletion syndrome, which is mainly caused by TBX1 gene mutations. Thus, we hypothesized that altered TBX1 gene expression may contribute to IIH development. In this study, the human TBX1 gene promoter was genetically analyzed in children with IIH (n = 100) and ethnic-matched controls (n = 167). Functions of DNA sequence variants (DSVs) within the TBX1 gene promoter were examined in cultured human fibroblast cells. The results showed that two heterozygous DSVs were found, both of which were single nucleotide polymorphisms. One DSV, g.4248 C>T (rs41298629), was identified in a 2-year-old boy with right-sided IIH, but not in all controls, which significantly decreased TBX1 gene promoter activity. Another DSV, g.4199 C>T (rs41260844), was found in both IIH patients and controls with similar frequencies (P > 0.05), which did not affect TBX1 gene promoter activity. Collectively, our data suggested that the DSV within the TBX1 gene promoter may change TBX1 level, contributing to IIH development as a rare risk factor. Underlying molecular mechanisms need to be established.     

Effect of FGF-1 and FGF-2 on VEGF binding to human umbilical vein endothelial cells

When FGF-1 or FGF-2 and VEGF were added together, the mitogenic effect of FGF-1 or FGF-2 and VEGF on HUVEC was additive. However, when HUVECs were preincubated for 2 days with 10 ng/ml FGF-1 in the absence of VEGF, the Scatchard plot of [125I]VEGF binding sites was shifted to the right: both affinity classes of VEGF binding sites were equally affected, such that the total number of sites increased twofold. It is suggested that this type of interaction may be related to tumor angiogenesis and wound repair.