Transcriptional regulation of PRPF31: the role of variable gene expression in determining phenotype in retinitis pigmentosa
Professor Shomi Bhattacharya - Institute of Ophthalmology
Jointly funded by The Astor Foundation and the Rosetrees Charitable Trust
Description of Project:
Mutations in PRPF31 have been implicated in autosomal dominant retinitis pigmentosa (adRP) for over a decade, yet the molecular basis underlying the observed phenotypic non-penetrance in families remains unknown. In the population, there are differentially expressed alleles of PRPF31: both high-expressivity and a low-expressivity alleles. Inheritance of a higher-expressivity allele alongside a mutant allele provides protection against the clinical manifestations of the disease. The aim of the research was to investigate phenotypic non-penetrance associated with PRPF31 mutations, through the understanding of transcriptional regulation of PRPF31 in both health and disease.
Firstly, it was investigated whether the non-penetrant effect was caused by a cis- or trans-acting factor. Microsatellite data was used to show that inheritance of the wildtype chromosome 19q13 determined affection status of individuals harbouring a mutation in PRPF31. It was, therefore, concluded that a cis-acting element controls the non-penetrant phenotype.
A family affected by adRP with a history of non-penetrance was identified and a large deletion (112kb) in the 19q13.4 region encompassing PRPF31 was fully characterized. Importantly, the deletion encompassed all introns of PRPF31 and also a large region upstream, therefore including putative regulatory elements of the gene.
Dual-luciferase reporter assay was performed to define the core promoter of PRPF31 and also the core promoter of TFPT, a gene lying in a head-to-head arrangement with PRPF31, with partially shared exon 1. Core promoters were defined for both genes. A patient with a history of isolated adRP was identified, in whom a single base pair deletion in the PRPF31 core promoter was present. Functional studies were performed, demonstrating that the mutant allele had a serious adverse affect on transcription of PRPF31- this patient represents the first report of functional haploinsufficiency as a disease mechanism in adRP.
Comparison of the PRPF31 core promoter sequence in an asymptomatic and a symptomatic individual lead to the identification of one polymorphism that significantly affected transcriptional activation of the gene and it was found that this polymorphism was statistically under-represented in a cohort of symptomatic individuals compared to the general population. This represents the first identification of a molecular factor controlling non-penetrance in PRPF31-associated adRP.
Finally, the evolution of the PRPF31 and TFPT core promoters was studied. The conservation of the region was analysed and regions homologous to the human core promoter fragments were sought in monkey, dog and mouse. Dual-reporter luciferase assay was performed to characterise the promoter elements in these three species, and demonstrated that conservation of a gene was not always accompanied by conservation of regulatory elements.
Rose AM, Webster AR, Mukhopadhyay R, Bhattacharya SS, Waseem NH. Identification of Large Deletions in PRPF31 in Autosomal Dominant Retinitis Pigmentosa. IOVS 2010; 51:ARVO E-Abstract 4093
Rose AM, Gradin DS, Mundia D. Bilateral lens subluxation in a patient with suspected Loeys-Dietz syndrome. Afr J Paediatr Surg 2011; 8:119-20.
Rose AM, Kabiru J, Rose GE. Alveolar soft-part sarcoma of the orbit. Afr J Paediatr Surg 2011; 8:82-4.
Rose AM, Mukhopadhyay R, Webster AR, Bhattacharya SS, Waseem NH. A 112kb deletion in chromosome 19q13.42 leads to retinitis pigmentosa. IOVS 2011; 52:6597-6603. Mitchison NA, Rose AM. Epistasis: The key to understanding immunological disease? Eur J Immunol 2011; 41:2152–2154.
Rose AM, Shah AZ, Waseem NH, Chakarova CF, Alfano G, Coussa RG, Ajlan R, Koenekoop RK, Bhattacharya SS. Expression of PRPF31 and TFPT: regulation in health and retinal disease. Hum Mol Genet 2012; 21:4126-37.
Rose AM, Bell LCK. Epistasis and immunity: the role of genetic interactions in autoimmune diseases. Immunology 2012; 137:131-8.
Venturini G, Rose AM, Shah AZ, Bhattacharya SS, Rivolta C. CNOT3 is a modifier of PRPF31 mutations in retinitis pigmentosa with incomplete penetrance. PLoS Genetics 2012; 8(11):e1003040
Rose AM, Kabiru J, Rose GE. A rare case of orbital haemangiopericytoma arising in childhood. Orbit 2013; 32(6):384-6.
Rose AM, Shah AZ, Alfano G, Bujakowska KM, Barker AF, Robertson JL, Rahman S, Valdez Sanchez L, Diaz-Corrales F, Chakarova CF, Krishna A, Bhattacharya SS. A study into the evolutionary divergence of the core promoter elements of PRPF31 and TFPT. J Mol Genet Med 2013; 7:67.
Rose AM, Shah AZ, Venturini G, Rivolta C, Rose GE, Bhattacharya SS. Dominant PRPF31 mutations are hypostatic to a recessive CNOT3 polymorphism in retinitis pigmentosa: A Novel Phenomenon of "Linked Trans-Acting Epistasis." Annals of Human Genetics 2013; in press.
Rose AM, Hall CS, Martinez-Alier N. Aetiology and management of malnutrition in HIV-positive children. Archives of Disease in Childhood 2014; ePub ahead of print.
Prizes and Awards
SELECTED UNIVERSITY ACADEMIC AWARDS
- Division of Biosciences Faculty Medal 2008-9 Nominee
- Cordwainer's Prize for Best MBPhD thesis – January 2013
- Allen Goldsmith Prize for Cancer Medicine – June 2013
- John Jepson Memorial Prize for the Scientific Basis of Medicine – June 2013
NATIONAL ACADEMIC AWARDS
- Royal Society of Medicine (Ophthalmology Section and Student Members Group) UCO 2009 Best Case Presentation – April 2009
- Royal Society of Medicine Student Research Prize (First Place) – November 2009
- Link: http://www.ucl.ac.uk/news/news-articles/0911/09111001
- Royal Society of Medicine Brigadier Haywood prize (shortlisted) – February 2010
- Royal College of Paediatrics and Child Health Tony Jackson Prize – January 2012
- Link: http://www.ucl.ac.uk/news/news-articles/February2012/16022012-ucl-studen...
- Medical Acorn Foundation Conference Best Oral Presentation (Medicine) – October 2012
- Royal College of Ophthalmologists' Duke Elder Prize Examination – May 2013