MOLECULAR CHARACTERIZATION AND DEVELOPMENTAL EXPRESSION OF THE XENOPUS EMERIN
Gareiß M.1, Zentgraf H.2, Wilken N.1, Müller C.R.3 and Dabauvalle M.-C.1
1Department of Cell and Developmental Biology, and 3Department of Human Genetics, Biocenter, University of Wuerzburg, and 2German Cancer Research Center, Heidelberg, Germany
Emery-Dreifuss muscular dystrophy (EDMD) is an X-linked disease due to mutations in emerin. Emerin is an ubiquitous transmembrane protein of the inner nuclear membrane. While the protein is expressed in the majority of human tissues analyzed, the pathology predominates in cardiac and skeletal muscle of EDMD patients. For a better understanding of the functions of emerin in the organisation of the cell nucleus, we decided to characterize and to investigate its role in vivo and in vitro in Xenopus laevis as a model system.
By cDNA cloning and sequenzing we have characterized X-emerin, a Xenopus homologue of the mammalian emerin. Analysis of the amino acid sequence resulted in a polypeptide with 180 residues and a calculated molecular mass of 21,6 kDa (24 kDa on SDS-PAGE). A motif screen of the protein showed an LEM domain (N1-C44) and a transmembrane motif in the C-terminus (N147-C169). Sequence comparison showed a homology of 52 % to the human and 53 % to the murine emerin. We have generated monoclonal antibodies specific for Xenopus emerin. The analysis of emerin expression during development revealed that X-emerin was absent from oocytes and from early developmental stages and was first detectable at tadpole stage 43. Interestingly, the expression of the lamin A started approximately at the same developmental stage (stage 40). Whole mount in situ immunolocalisation and hybridizations were performed to study the expression pattern of emerin. Since emerin as well as lamin A is not expressed in oocytes and eggs, it is possible to study the effect of exogenously expressed emerin, in the presence or absence of lamin A, on the nuclear envelope assembly, on the nuclear structure and on the chromatin organization in oocytes, in early embryogenesis and in a cell free extract prepared from Xenopus eggs.
THE WILHELM BERNHARD JUNIOR LECTURE
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