Limb-girdle muscular dystrophy type 2O (LGMD2O) belongs to a group of rare muscular dystrophies named dystroglycanopathies, which are molecularly characterized by hypoglycosylation of α-dystroglycan and present a wide clinical spectrum ranging from congenital muscular dystrophy associated with severe brain and eye malformation to mild forms of muscle weakness with later onset and without brain involvement. We report the first mutation in the promoter region of POMGNT1 gene in a LGMD2O patient, consisting in a 9-bp duplication in homozygous state. By analyzing the downstream effects of this alteration we found a decreased expression of POMGNT1 mRNA and protein in our patient due to a negative regulation exerted by ZFN202 transcription factor. By functional analysis of a series of deletion constructs we localized the proximal promoter region between -402 and +644 bp relative to the transcription start site and found a 75% decrease of luciferase activity of the construct carrying the new mutation compared with the wild type construct. Electrophoretic mobility shift assay revealed that this region contains three Sp1, one Ets1 and one GATA transcription factor binding sites. The three Sp1 sites were confirmed by chromatin immunoprecipitation assay. Surprisingly, the reported mutation generated an additional ZNF202 binding site and caused a strong binding of this transcriptional repressor to the mutated POMGNT1 promoter, whereas it did not recognize the wild type promoter. These studies underline the importance of the promoter regions for adequate gene expression and the association of certain types of dystroglycanopathies with the impairment of yet-unknown regulatory mechanisms.

Póster presentado al XXXI Congreso de la Sociedad Española de Bioquímica y Biología Molecular, celebrado en Barcelona del 5 al 8 de septiembre de 2011.-- et al.

Funding: Instituto de Salud Carlos III PI09/0343 (J.C) and PI09/1623 (J.M.N).

Peer Reviewed