Incomplete penetrance and phenotypic variability characterize Gdf6-attributable oculo-skeletal phenotypes

Department of Ophthalmology, University of Alberta, Edmonton, Canada.
Human Molecular Genetics (Impact Factor: 6.39). 02/2009; 18(6):1110-21. DOI: 10.1093/hmg/ddp008
Source: PubMed


Proteins of the bone morphogenetic protein (BMP) family are known to have a role in ocular and skeletal development; however, because of their widespread expression and functional redundancy, less progress has been made identifying the roles of individual BMPs in human disease. We identified seven heterozygous mutations in growth differentiation factor 6 (GDF6), a member of the BMP family, in patients with both ocular and vertebral anomalies, characterized their effects with a SOX9-reporter assay and western analysis, and demonstrated comparable phenotypes in model organisms with reduced Gdf6 function. We observed a spectrum of ocular and skeletal anomalies in morphant zebrafish, the latter encompassing defective tail formation and altered expression of somite markers noggin1 and noggin2. Gdf6(+/-) mice exhibited variable ocular phenotypes compatible with phenotypes observed in patients and zebrafish. Key differences evident between patients and animal models included pleiotropic effects, variable expressivity and incomplete penetrance. These data establish the important role of this determinant in ocular and vertebral development, demonstrate the complex genetic inheritance of these phenotypes, and further understanding of BMP function and its contributions to human disease.

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Available from: Veronica Van Heyningen, Oct 04, 2015
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    • "Growth differentiation factor 5 (GDF5/BMP-14/CDMP-1) and growth differentiation factor 6 (GDF6/BMP-13/CDMP-2) are members of the TGF superfamily and are associated with skeletal development [13-15]. We previously demonstrated that they are expressed by human NP cells and that GDF5 increases type II collagen and aggrecan gene expression by degenerate human NP cells in vitro[16]. "
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    ABSTRACT: Currently, there is huge research focus on the development of novel cell based regeneration and tissue engineering therapies for the treatment of intervertebral disc degeneration and the associated back pain. Both bone marrow-derived (BM) mesenchymal stem cells (MSCs) and adipose-derived MSCs (AD-MSCs) are proposed as suitable cells for such therapies. However, currently there is no consensus as to the optimum growth factor needed to drive differentiation to a nucleus pulposus (NP)-like phenotype. The aim of this study was to investigate the effect of growth differentiation factor-6 (GDF6), compared to other transforming growth factor (TGF) superfamily members, on discogenic differentiation of MSCs, the matrix composition and micromechanics of engineered NP tissue constructs. Patient-matched human AD-MSCs and BM-MSCs were seeded into type I collagen hydrogels and cultured in a differentiating media supplemented with TGF-beta3, GDF5 or GDF6. After 14 days quantitative polymerase chain reaction analysis of chondrogenic and novel NP marker genes and sulphated glycosaminoglycan (sGAG) content of the construct and media components were analyzed. Additionally, construct micromechanics were analyzed using scanning acoustic microscopy (SAM). GDF6 stimulation of BM-MSCs and AD-MSCs resulted in a significant increase in expression of novel NP marker genes, a higher aggrecan to type II collagen gene expression ratio and higher sGAG production compared to TGF-beta or GDF5 stimulation. These effects were greater in AD-MSCs than BM-MSCs. Furthermore, the acoustic wave speed measured using SAM, and therefore tissue stiffness, was lowest in GDF6-stiumlated AD-MSC constructs. The data suggest that GDF6 stimulation of AD-MSCs induces differentiation to an NP-like phenotype and results in a more proteoglycan-rich matrix. Micromechanical analysis shows that the GDF6 treated AD-MSCs have a less stiff matrix composition suggesting the growth factor is inducing a matrix that is more akin to the native NP-like tissue. Thus, this cell and growth factor combination may be the ideal choice for cell-based intervertebral disc regeneration therapies.
    Arthritis research & therapy 03/2014; 16(2):R67. DOI:10.1186/ar4505 · 3.75 Impact Factor
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    • "A further alternative explanation for deficits in swimming performance could be morphological changes resulting from long-term loss of gdf6a. Skeletal changes might be anticipated from BMP namesake functions in bone morphogenesis, from skeletal defects observed in patients with GDF6 mutations [39]–[42] or past analysis of zebrafish gdf6a morphants [43]. In adult zebrafish, skeletal deficits in the axial skeleton were not observed (Figure 1, Supplemental Movie S1). "
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    ABSTRACT: Mutation of Glass bottom boat, the Drosophila homologue of the bone morphogenetic protein or growth/differentiation factor (BMP/GDF) family of genes in vertebrates, has been shown to disrupt development of neuromuscular junctions (NMJ). Here we tested whether this same conclusion can be broadened to vertebrate BMP/GDF genes. This analysis was also extended to consider whether such genes are required for NMJ maintenance in post-larval stages, as this would argue that BMP genes are viable candidates for analysis in progressive neuromuscular disease. Zebrafish mutants harboring homozygous null mutations in the BMP-family gene gdf6a were raised to adulthood and assessed for neuromuscular deficits. Fish lacking gdf6a exhibited decreased endurance (∼50%, p = 0.005) compared to wild type, and this deficit progressively worsened with age. These fish also presented with significantly disrupted NMJ morphology (p = 0.009), and a lower abundance of spinal motor neurons (∼50%, p<0.001) compared to wild type. Noting the similarity of these symptoms to those of Amyotrophic Lateral Sclerosis (ALS) model mice and fish, we asked if mutations in gdf6a would enhance the phenotypes observed in the latter, i.e. in zebrafish over-expressing mutant Superoxide Dismutase 1 (SOD1). Amongst younger adult fish only bigenic fish harboring both the SOD1 transgene and gdf6a mutations, but not siblings with other combinations of these gene modifications, displayed significantly reduced endurance (75%, p<0.05) and strength/power (75%, p<0.05), as well as disrupted NMJ morphology (p<0.001) compared to wild type siblings. Bigenic fish also had lower survival rates compared to other genotypes. Thus conclusions regarding a role for BMP ligands in effecting NMJ can be extended to vertebrates, supporting conservation of mechanisms relevant to neuromuscular degenerative diseases. These conclusions synergize with past findings to argue for further analysis of GDF6 and other BMP genes as modifier loci, potentially affecting susceptibility to ALS and perhaps a broader suite of neurodegenerative diseases.
    PLoS ONE 02/2014; 9(2):e89183. DOI:10.1371/journal.pone.0089183 · 3.23 Impact Factor
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    • "Despite the critical role of gdf6a for dorsal retina initiation in zebrafish, a similar role for this factor in other species has not been described. In other vertebrates, Gdf6 is expressed in the dorsal retina and its loss results in a variety of ocular malformations including colobomata, microphthalmia and anopthalmia (Asai-Coakwell et al., 2007; Asai-Coakwell et al., 2009; Hanel and Hensey, 2006). These gross anatomical phenotypes may be a result of defective dorsal–ventral patterning in these species as well. "
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    ABSTRACT: Dorsal retinal fate is established early in eye development, via expression of spatially restricted dorsal-specific transcription factors in the optic vesicle; yet the events leading to initiation of dorsal fate are not clear. We hypothesized that induction of dorsal fate would require an extraocular signal arising from a neighboring tissue to pattern the prospective dorsal retina, however no such signal has been identified. We used the zebrafish embryo to determine the source, timing, and identity of the dorsal retina-inducing signal. Extensive cell movements occur during zebrafish optic vesicle morphogenesis, however the location of prospective dorsal cells within the early optic vesicle and their spatial relationship to early dorsal markers is currently unknown. Our mRNA expression and fate mapping analyses demonstrate that the dorsolateral optic vesicle is the earliest region to express dorsal specific markers, and cells from this domain contribute to the dorsal retinal pole at 24hpf. We show that three bmp genes marking dorsal retina at 25hpf are also expressed extraocularly before retinal patterning begins. We identified gdf6a as a dorsal initiation signal acting from the extraocular non-neural ectoderm during optic vesicle evagination. We find that bmp2b is involved in dorsal retina initiation, acting upstream of gdf6a. Together, this work has identified the nature and source of extraocular signals required to pattern the dorsal retina.
    Developmental Biology 08/2012; 371(1):57-65. DOI:10.1016/j.ydbio.2012.08.004 · 3.55 Impact Factor
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