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Molecular and Cellular Biology, January 2006, p. 605-616, Vol. 26, No. 2
0270-7306/06/$08.00+0 doi:10.1128/MCB.26.2.605-616.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Experimental Mouse Genetics,1 Laboratory for Neuronal Cell Biology, Center for Human Genetics, KU Leuven and Flanders Interuniversity Institute for Biotechnology, B-3000 Leuven, Belgium2
Received 25 August 2005/ Returned for modification 18 September 2005/ Accepted 16 October 2005
Lrp1 knock-in mice carrying either a wild-type allele or three different mutated alleles encoding the multifunctional endocytic receptor LRP1 were generated by recombinase-mediated cassette exchange (RMCE). Reinsertion by RMCE of a wild-type allele led to a normal pattern and level of gene expression and a completely normal phenotype, indicating that the RMCE procedure itself is neutral with respect to the function of the gene locus. In contrast, reinsertion of mutated LRP1 alleles carrying either inactivating mutations in the proximal NPXY motif (NPTY
AATA) of the cytoplasmic domain or in the furin cleavage site (RHRR
AHAA) caused distinctive liver phenotypes: respectively, either a late fetal destruction of the organ causing perinatal death or a selective enlargement of von-Kupffer cell lysosomes reminiscent of a mild lysosomal storage without an apparent negative effect on animal survival. Notably, mutation of the distal NPXY motif overlapping with an YXXL motif (NPVYATL
AAVAATL) did not cause any obvious pathological effect. The mutations showed no effect on the LRP1 expression level; however, as expected, the proteolytic maturation of LRP1 into its two subunits was significantly impaired, although not completely abolished, in the furin cleavage mutant. These data demonstrate that RMCE is a reliable and efficient approach to generate multiple mutant knock-in alleles for in vivo functional analysis of individual domains or motifs of large multidomain proteins. Its application in Lrp1 reveals dramatically variant phenotypes, of which further characterization will definitively contribute to our understanding of the biology of this multifunctional receptor.
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