A Dominant-Negative Mutation of Mouse Lmx1b Causes Glaucoma and Is Semi-lethal via LBD1-Mediated Dimerisation

Abstract

Mutations in the LIM-homeodomain transcription factor LMX1B cause nail-patella syndrome, an autosomal dominant pleiotrophic human disorder in which nail, patella and elbow dysplasia is associated with other skeletal abnormalities and variably nephropathy and glaucoma. It is thought to be a haploinsufficient disorder. Studies in the mouse have shown that during development Lmx1b controls limb dorsal-ventral patterning and is also required for kidney and eye development, midbrain-hindbrain boundary establishment and the specification of specific neuronal subtypes. Mice completely deficient for Lmx1b die at birth. In contrast to the situation in humans, heterozygous null mice do not have a mutant phenotype. Here we report a novel mouse mutant Icst, an N-ethyl-N-nitrosourea-induced missense substitution, V265D, in the homeodomain of LMX1B that abolishes DNA binding and thereby the ability to transactivate other genes. Although the homozygous phenotypic consequences of Icst and the null allele of Lmx1b are the same, heterozygous Icst elicits a phenotype whilst the null allele does not. Heterozygous Icst causes glaucomatous eye defects and is semi-lethal, probably due to kidney failure. We show that the null phenotype is rescued more effectively by an Lmx1b transgene than is Icst. Co-immunoprecipitation experiments show that both wild-type and Icst LMX1B are found in complexes with LIM domain binding protein 1 (LDB1), resulting in lower levels of functional LMX1B in Icst heterozygotes than null heterozygotes. We conclude that Icst is a dominant-negative allele of Lmx1b. These findings indicate a reassessment of whether nail-patella syndrome is always haploinsufficient. Furthermore, Icst is a rare example of a model of human glaucoma caused by mutation of the same gene in humans and mice.

Nail–Patella Syndrome: clinical and molecular data in 55 families raising the hypothesis of a genetic heterogeneity

“…Furthermore, recent studies in mice have demonstrated that missense variants of the HD can show dominant-negative activity in vivo. 15 In the present study, we describe the phenotype and molecular data of 55 index patients and their 39 relatives affected with NPS. Variants or large rearrangements of LMX1B were identified in 91% of patients.…”

Genome wide-association study identifies novel loci in the Primary Open-Angle African American Glaucoma Genetics (POAAGG) study

“…71 A dominant negative mutation of mouse Lmx1b (Lmx1b Icst/+ ) also causes glaucoma and is semi-lethal. 72 The COL19A1 gene encodes the alpha chain of type XIX collagen, a member of the FACIT collagen family (fibril-associated collagens with interrupted helices). Decreased expression of Col19A1 (1.9 fold) was observed in a microarray of an 8-month old DBA/2J mouse retina when compared to 3-month-old retina.…”

Inherited Eye Diseases with Retinal Manifestations through the Eyes of Homeobox Genes

“…An N-ethyl-N-nitrosourea-induced missense substitution, V265D, in the homeodomain of mouse Lmx1b abolishes DNA binding and causes glaucomatous eye defects in heterozygotes. A profound reduction in the number of retinal ganglion cells and optic nerve cupping was observed in some cases [147].…”