title: Analysis of naturally occurring mutations in the human lipodystrophy protein seipin reveals multiple potential pathogenic mechanisms.
abstract: OBJECTIVE
  In humans, disruption of the gene BSCL2, encoding the protein seipin, causes congenital generalised lipodystrophy (CGL) with severe insulin resistance and dyslipidaemia. While the causative gene has been known for over a decade, the molecular functions of seipin are only now being uncovered. Most pathogenic mutations in BSCL2 represent substantial disruptions including significant deletions and frameshifts. However, several more subtle mutations have been reported that cause premature stop codons or single amino acid substitutions. Here we have examined these mutant forms of seipin to gain insight into how they may cause CGL.
  
  
  METHODS
  We generated constructs expressing mutant seipin proteins and determined their expression and localisation. We also assessed their capacity to recruit the key adipogenic phosphatidic acid phosphatase lipin 1, a recently identified molecular role of seipin in developing adipocytes. Finally, we used atomic force microscopy to define the oligomeric structure of seipin and to determine whether this is affected by the mutations.
  
  
  RESULTS
  We show that the R275X mutant of seipin is not expressed in pre-adipocytes. While the other premature stop mutant forms fail to bind lipin 1 appropriately, the point mutants T78A, L91P and A212P all retain this capacity. We demonstrate that wild-type human seipin forms oligomers of 12 subunits in a circular configuration but that the L91P and A212P mutants of seipin do not.
  
  
  CONCLUSIONS
  Our study represents the most comprehensive analysis so far of mutants of seipin causing lipodystrophy and reveals several different molecular mechanisms by which these mutations may cause disease.
authors.affiliation: University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, UK.
authors.forename: M F Michelle
authors.initials: MF
authors.lastname: Sim
authors.forename: M Mesbah Uddin
authors.initials: MM
authors.lastname: Talukder
authors.forename: Rowena J
authors.initials: RJ
authors.lastname: Dennis
authors.forename: Stephen
authors.initials: S
authors.lastname: O'Rahilly
authors.forename: J Michael
authors.initials: JM
authors.lastname: Edwardson
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Rochford
mesh_terms: D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D044388:GTP-Binding Protein gamma Subunits / Q000235:genetics / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008060:Lipodystrophy / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D018625:Microscopy, Atomic Force; D009154:Mutation
chemical_list: C432679:BSCL2 protein, human; C115783:Bscl2 protein, mouse; D044388:GTP-Binding Protein gamma Subunits; D020962:Heterotrimeric GTP-Binding Proteins