International Mammalian Genome Society

The 16th International Mouse Genome Conference (2002)


J Peters
Medical Research Council

1) Nottingham W, 1) Ball S, 2) Plagge A, 1) Maconochie M, 2) Kelsey G, 1) Williamson C
1) MRC Mammalian Genetics Unit, 2) The Babraham Institute

An increasing number of imprinted genes have antisense RNAs associated with them and some have been shown to play an active role in genomic imprinting.  Within the Gnas complex in distal mouse chromosome 2 are several antisense RNAs, all of which are imprinted, paternally expressed, and non-coding.  In addition to an unspliced form of about 30 kb, there are a number of alternatively spliced forms that are up to 1.4 kb in length. These antisense RNAs are called Nespas.  Nespas overlaps the maternally expressed gene Nesp within the Gnas complex, but is unlikely to regulate the expression of Nesp in mid gestation embryos because Nespas and Nesp are expressed in different sites.  Nespas may regulate Nesp at earlier developmental stages.  Other studies to examine the role of Nespas have been hampered by the close proximity of Gnasxl, a paternally expressed protein-encoding gene. Analysis of the 2 kb of sequence that separates the first exons of Nespas and Gnasxl has shown that their minimal promoter regions do not overlap and that the Nespas promoter lies within 500 bp of the start site.  A gene targeting approach to delete the Nespas promoter and first exon is in progress.  Homologous recombination in yeast was used to generate the targeting construct in which a tACE-Cre cassette was included for self-excision of selection markers in the male germline.  Targeting has been performed in male ES cells and fourteen targeted clones have been identified.

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