Eye and neural defects associated with loss of GDF6

BACKGROUND: In Xenopus the bone morphogenetic protein growth and differentiation factor 6 (GDF6) is expressed at the edge of the neural plate, and within the anterior neural plate including the eye fields. Here we address the role of GDF6 in neural and eye development by morpholino knockdown experiments. RESULTS: We show that depletion of GDF6 (BMP13) resulted in a reduction in eye size, loss of laminar structure and a reduction in differentiated neural cell types within the retina. This correlated with a reduction in staining for Smad1/5/8 phosphorylation indicating a decrease in GDF6 signalling through loss of phosphorylation of these intracellular mediators of bone morphogenetic protein (BMP) signalling. In addition, the Pax6 expression domain is reduced in size at early optic vesicle stages. Neural cell adhesion molecule (NCAM) is generally reduced in intensity along the neural tube, while in the retina and brain discreet patches of NCAM expression are also lost. GDF6 knock down resulted in an increase in cell death along the neural tube and within the retina as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. CONCLUSION: Our data demonstrate that GDF6 has an important role in neural differentiation in the eye as well as within the central nervous system, and that GDF6 may act in some way to maintain cell survival within the ectoderm, during the normal waves of programmed cell death

FSHD region gene 1 (FRG1) is crucial for angiogenesis linking FRG1 to facioscapulohumeral muscular dystrophy-associated vasculopathy

The genetic lesion that is diagnostic for facioscapulohumeral muscular dystrophy (FSHD) results in an epigenetic misregulation of gene expression, which ultimately leads to the disease pathology. FRG1 (FSHD region gene 1) is a leading candidate for a gene whose misexpression might lead to FSHD. Because FSHD pathology is most prominent in the musculature, most research and therapy efforts focus on muscle cells. Previously, using Xenopus development as a model, we showed that altering frg1 expression levels systemically leads to aberrant muscle development, illustrating the potential for aberrant FRG1 levels to disrupt the musculature. However, 50–75% of FSHD patients also exhibit retinal vasculopathy and FSHD muscles have increased levels of vascular- and endothelial-related FRG1 transcripts, illustrating an underlying vascular component to the disease. To date, no FSHD candidate gene has been proposed to affect the vasculature. Here, we focus on a role for FRG1 expression in the vasculature. We found that endogenous frg1 is expressed in both the developing and adult vasculature in Xenopus. Furthermore, expression of FRG1 was found to be essential for the development of the vasculature, as a knockdown of FRG1 resulted in decreased angiogenesis and reduced expression of the angiogenic regulator DAB2. Conversely, tadpoles subjected to frg1 overexpression displayed the pro-angiogenic phenotypes of increased blood vessel branching and dilation of blood vessels, and developed edemas, suggesting that their circulation was disrupted. Thus, the systemic upregulation of the FRG1 protein shows the potential for acquiring a disrupted vascular phenotype, providing the first link between a FSHD candidate gene and the vascular component of FSHD pathology. Overall, in conjunction with our previous analysis, we show that FRG1 overexpression is capable of disrupting both the musculature and vasculature, recapitulating the two most prominent features of FSHD

Tissue-specific and imprinted epigenetic modifications of the human NDN gene

Allele-specific DNA methylation, histone acetylation and histone methylation are recognized as epigenetic characteristics of imprinted genes and imprinting centers (ICs). These epigenetic modifications are also used to regulate tissue-specific gene expression. Epigenetic differences between alleles can be significant either in the function of the IC or in the cis-acting effect of the IC on ‘target’ genes responding to it. We have now examined the epigenetic characteristics of NDN, a target gene of the chromosome 15q11–q13 Prader–Willi Syndrome IC, using sodium bisulfite sequencing to analyze DNA methylation and chromatin immunoprecipitation to analyze histone modifications. We observed a bias towards maternal allele-specific DNA hypermethylation of the promoter CpG island of NDN, independent of tissue-specific transcriptional activity. We also found that NDN lies in a domain of paternal allele-specific histone hyperacetylation that correlates with transcriptional state, and a domain of differential histone H3 lysine 4 di- and tri-methylation that persists independent of transcription. These results suggest that DNA methylation and histone H3 lysine 4 methylation are persistent markers of imprinted gene regulation while histone acetylation participates in tissue-specific activity and silencing in somatic cells