title: Hypomorphic expression of Dkk1 in the doubleridge mouse: dose dependence and compensatory interactions with Lrp6.
abstract: doubleridge is a transgene-induced mouse mutation displaying forelimb postaxial polysyndactyly. We have cloned the doubleridge transgene insertion site and demonstrate that doubleridge acts in cis from a distance of 150 kb to reduce the expression of dickkopf 1 (Dkk1), the secreted Wnt antagonist. Expression of Dkk1 from the doubleridge allele ranges from 35% of wild-type level in E7.0 head to <1% of wild type in E13.5 tail. doubleridge homozygotes and doubleridge/null compound heterozygotes are viable. An allelic series combining the wild-type, doubleridge and null alleles of Dkk1 demonstrates the effect of varying Dkk1 concentration on development of limb, head and vertebrae. Decreasing expression of Dkk1 results in hemivertebral fusions in progressively more anterior positions, with severity increasing from tail kinks to spinal curvature. We demonstrated interaction between Dkk1 and the Wnt coreceptors Lrp5 and Lrp6 by analysis of several types of double mutants. The polydactyly of Dkk1(d/d) mice was corrected by reduced expression of Lrp5 or Lrp6. The posterior digit loss and axial truncation characteristic of Lrp6 null mice was partially corrected by reduction of Dkk1. Similarly, the anterior head truncation characteristic of Dkk1 null mice was rescued by reduction of Lrp6. These compensatory interactions between Dkk1 and Lrp6 demonstrate the importance of correctly balancing positive and negative regulation of Wnt signaling during mammalian development.
authors.affiliation: Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109-0618, USA.
authors.forename: Bryan T
authors.initials: BT
authors.lastname: MacDonald
authors.forename: Maja
authors.initials: M
authors.lastname: Adamska
authors.forename: Miriam H
authors.initials: MH
authors.lastname: Meisler
mesh_terms: D000818:Animals; D001483:Base Sequence; D002875:Chromosomes; D003001:Cloning, Molecular; D004251:DNA Transposable Elements; D005091:Exons; D005313:Fetal Death / Q000235:genetics; D018628:Gene Dosage; D018507:Gene Expression Regulation, Developmental; D015321:Gene Rearrangement; D005816:Genetic Complementation Test; D006257:Head / Q000002:abnormalities / Q000196:embryology; D036341:Intercellular Signaling Peptides and Proteins; D026502:LDL-Receptor Related Proteins; D017880:Limb Deformities, Congenital / Q000196:embryology / Q000235:genetics; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D051379:Mice; D008817:Mice, Mutant Strains; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D011973:Receptors, LDL / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D013131:Spine / Q000002:abnormalities / Q000196:embryology; D013576:Syndactyly / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; C501127:Dkk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D026502:LDL-Receptor Related Proteins; C555482:LRP5 protein, human; C555475:LRP6 protein, human; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; C555483:Lrp5 protein, mouse; C555476:Lrp6 protein, mouse; D011506:Proteins; D011973:Receptors, LDL