3-M syndrome (named after three authors who first described the condition) is an autosomal recessive condition characterised by pre- and post-natal growth impairment, facial dysmorphism and radiological features (slender long bones and tall vertebral bodies). It is caused by loss of function mutations in the Cullin 7 (CUL7) and Obscurin-like 1 (OBSL1) genes. CUL7 is a protein involved in ubiquitination (the process of targeted protein degradation) and OBSL1 is a putative cytoskeletal adaptor protein. The mechanisms through which loss of function mutations in OBSL1 or CUL7 lead to growth impairment is unclear but previous work suggests impaired placental function and altered insulin-like growth factor 1 (IGF-1) signaling as possibilities. The overall aim of this study was to elucidate the mechanisms underlying growth impairment in 3-M syndrome. Initially phenotypic data was collected on a cohort of patients and a genotype-phenotype comparison was undertaken. Skin fibroblast cell lines were derived from four patients with 3-M syndrome and used to study growth hormone (GH) and IGF-1 signal transduction, cell proliferation and apoptosis. Subsequently a hypothesis generating approach to identify novel mechanisms underlying 3-M growth impairment was undertaken in whole transcriptome and metabolomic studies. In addition an animal model using morpholino oligonucleotide mediated knock down of OBSL1 in Xenopus tropicalis was developed to study the effects on growth in a non placenting vertebrate to determine if the growth impairment seen in 3-M syndrome is independent of placental function. Cell proliferation was reduced in 3-M fibroblasts while apoptosis was not different from controls. No differences in GH signal transduction were identified but reduced activation of AKT following IGF-1 stimulation was identified in 3-M fibroblast cell lines. IGF2 was identified as the top downregulated probeset in 3-M fibroblasts compared to control in the whole genome transcriptome analysis. Metabolomic changes related to energy metabolism were identified in 3-M syndrome fibroblasts. Knock down of xtOBSL1 using two independent morpholinos resulted in growth impairment at embryonic stage 50, suggesting the growth impairment seen is at least in part independent of placental function. These studies suggest impaired placental function is not a key component of the growth impairment in 3-M syndrome. Impairment of IGF-1 signal transduction and IGF2 silencing are likely to contribute to the growth impairment in 3-M syndrome. The mechanisms relating to this IGF2 silencing require further studies.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:553338 |
| Date | January 2011 |
| Creators | Murray, Philip |
| Contributors | Clayton, Peter; Black, Graeme |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/a-clinical-and-molecular-study-of-the-growth-disorder-3m-syndrome(5509fea9-84a8-4883-9991-2a17d2fa4964).html |
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