Objective
X chromosome inactivation is the mechanism whereby mammals achieve dosage compensation for X-linked genes between XY males and XX females. Understanding the molecular basis of this unusual and enigmatic process provides an important goal in Mammalian Genetics.
Mouse embryonic stem (ES) cells have been used extensively in studies on the mechanism of X chromosome inactivation. The main aim of this project is to isolate XX ES cell lines from interspecific F1 vole species that show extreme non-random X inactivation. This will complement our ongoing studies aimed at understanding the molecular basis of non-random X inactivation in voles. Because derivation of ES cell lines can be difficult we will employ complementary strategies to ensure that the primary aim is achieved. Firstly we will work towards deriving XX Embryonic Germ (EG) cell lines, which are nearly equivalent to ES cells, at least for the studies proposed here. Secondly we will derive mouse ES cell lines carrying vole X chromosomes using a cell fusion strategy. Again these cells will provide an appropriate resource for studying non-random X inactivation. The novel cell lines derived in this study will be characterised in terms of X inactivation and also in terms of developmental potential. A longer term aim is to use these systems in gene targeting experiments aimed at testing specific models for non-random X inactivation.
This work builds on progress achieved in an INTAS funded project that was directed at characterisation of the Xist gene locus in vole species (INTAS 94-2877). The Xist locus is involved in regulating the initiation of X inactivation and is therefore likely to be central to understanding mechanisms of non-random X inactivation. As a result of the project we have identified candidate sequence variants in the Xist locus that may be responsible for non-random X inactivation in F1 vole hybrids. We anticipate that ongoing work will further refine candidate sequences. The cell systems that we plan to develop here will allow us to directly test specific candidate sequences.
The consortium involves the NIS group of Dr Suren Zakian who initiated studies into X inactivation in the vole system and two teams from INTAS countries who have played leading roles in studies on X inactivation in the mouse system. The NIS group of Dr Andrey Dyban have joined the consortium and bring expertise in the study of early pre-implantation development. Their role in carrying out in vivo aspects of the project will be of major importance.
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W12 0NN London
United Kingdom