Defective splicing of Megf7/Lrp4, a regulator of distal limb development, in autosomal recessive mulefoot disease

Abstract

Mulefoot disease (MFD) is an autosomal recessive disorder of phenotypically variable expression that causes syndactyly in certain strains of cows. MFD maps to a narrow interval on bovine chromosome 15 that is syntenic to human chromosome 11p12-p11.2. This region contains MEGF7/LRP4 (approved gene symbol LRP4), a gene that encodes a member of the multifunctional low-density lipoprotein receptor gene family. Targeted and naturally occurring mutations in the murine Megf7/Lrp4 gene, a putative coreceptor in the Wnt signaling pathway, cause polysyndactyly in the rodent. Thus, Megf7/Lrp4 is a strong candidate for the MFD mutation. Using PCR analysis of tissue samples and sperm from confirmed homozygous MFD carriers, we have identified a functional single base pair mutation in the affected animals. We show that a G --> A transition at the first nucleotide in the splice donor site of intron 37 completely disables this splice site. The abnormal splicing that is caused by this mutation predicts the generation of a dysfunctional membrane-anchored receptor lacking the normal cytoplasmic domain. These findings confirm that autosomal recessive loss-of-function mutations in Megf7/Lrp4 result in phenotypically similar forms of syndactyly in different mammalian species and that such mutations are the cause of MFD in bovines.

Agrin Binds to the N-terminal Region of Lrp4 Protein and Stimulates Association between Lrp4 and the First Immunoglobulin-like Domain in Muscle-specific Kinase (MuSK)

“…Hypomorphic mutations in human lrp4, which reduce Lrp4 expression, are responsible for Cenani Lenz syndrome, typified by defects in distal limb development and abnormal kidney differentiation (39). The ligands for Lrp4 in other tissues have not been well defined, but Lrp4 binds Dickkopf, Sclerostin, and Wnt modulator in surface ectoderm (WISE), modulators of Wnt and bone morphogenic protein (BMP) signaling (40,41), and genetic evidence supports the idea that Lrp4 can regulate Wnt and BMP signaling pathways (42). Although Lrp4 may simply sequester these regulators of Wnt and BMP signaling (41), these and other ligands may bind Lrp4 in a manner resembling Agrin or MuSK and induce conformational changes in Lrp4 that allow it to bind additional partners in these tissues.…”

Identifying novel genes involved in both deer physiological and human pathological osteoporosis

“…The role of LRP4 in bone development is conWrmed; LRP4 knockout mice exhibit signiWcantly delayed bone calciWcation as compared to the wild type (Johnson et al 2005). Furthermore, LRP4-deWciency has been implicated with various penetrance in polysyndactyly and abnormalities of tooth development (Johnson et al 2006;Simon-Chazottes et al 2006).…”

Expanding functions of lipoprotein receptors

“…It is unique in its size, which lies between the small members of the family (LDLR, Apoer2, and Vldlr) and the large receptors represented by LRP1, LRP1b, and LRP2. Several distinct strains of LRP4 mutant mice have been generated by gene targeting (42,43). LRP4 loss-of-function mutations have also spontaneously and independently arisen in several viable mouse and cattle strains (43)(44)(45)(46)(47).…”