Discovery and characterization of spontaneous mouse models of craniofacial dysmorphology

Craniofacial abnormalities are among the most common features of human genetic syndromes and disorders. The etiology of these conditions is often complex, influenced by both genetic context and the environment. Frequently, craniofacial abnormalities present as part of a syndrome with clear comorbid phenotypes, providing additional insight into mechanisms of the causative gene or pathway. The mouse has been a key tool in our understanding of the genetic mechanisms of craniofacial development and disease, and can provide excellent models for human craniofacial abnormalities. While powerful genetic engineering tools in the mouse have contributed significantly our understanding of craniofacial development and dysmorphology, forward genetic approaches provide an unbiased means to identify new genes and pathways. Moreover, spontaneous mutations can occur on any number of genetic backgrounds, potentially revealing critical genes that require a specific genetic context. Here we report discovery and phenotyping of 43 craniofacial mouse models, derived primarily from a screen for spontaneous mutations in production colonies at the Jackson Laboratory. We identify the causative gene for 33 lines, including novel genes in pathways not previously connected to craniofacial development, and novel alleles of known genes that present with unique phenotypes. Together with our detailed characterization, this work provides a valuable gene discovery resource for the craniofacial community, and a rich source of mouse models for further investigation.

A novel allele of Alx4 results in reduced Fgf10 expression and failure of eyelid fusion in mice

Normal fusion of developing eyelids requires coordination of inductive signals from the eyelid mesenchyme with migration of the periderm cell layer and constriction of the eyelids across the eye. Failure of this process results in an eyelids open at birth (EOB) phenotype in mice. We have identified a novel spontaneous allele of Alx4 that displays EOB, in addition to polydactyly and cranial malformations. Alx4 is expressed in the eyelid mesenchyme prior to and during eyelid fusion in a domain overlapping the expression of genes that also play a role in normal eyelid development. We show that Alx4 mutant mice have reduced expression of Fgf10, a key factor expressed in the mesenchyme that is required for initiation of eyelid fusion by the periderm. This is accompanied by a reduced number of periderm cells expressing phosphorylated c-Jun, consistent with the incomplete ablation of Fgf10 expression. Together, these data demonstrate that eyelid fusion in mice requires the expression of Alx4, accompanied by the loss of normal expression of essential components of the eyelid fusion pathway.

Mutation discovery in mice by whole exome sequencing

We report the development and optimization of reagents for in-solution, hybridization-based capture of the mouse exome. By validating this approach in a multiple inbred strains and in novel mutant strains, we show that whole exome sequencing is a robust approach for discovery of putative mutations, irrespective of strain background. We found strong candidate mutations for the majority of mutant exomes sequenced, including new models of orofacial clefting, urogenital dysmorphology, kyphosis and autoimmune hepatitis.

Disheveled hair and ear (Dhe), a spontaneous mouse Lmna mutation modeling human laminopathies

Background

Investigations of naturally-occurring mutations in animal models provide important insights and valuable disease models. Lamins A and C, along with lamin B, are type V intermediate filament proteins which constitute the proteinaceous boundary of the nucleus. LMNA mutations in humans cause a wide range of phenotypes, collectively termed laminopathies. To identify the mutation and investigate the phenotype of a spontaneous, semi-dominant mutation that we have named Disheveled hair and ear (Dhe), which causes a sparse coat and small external ears in heterozygotes and lethality in homozygotes by postnatal day 10.

Findings

Genetic mapping identified a point mutation in the Lmna gene, causing a single amino acid change, L52R, in the coiled coil rod domain of lamin A and C proteins. Cranial sutures in Dhe/+ mice failed to close. Gene expression for collagen types I and III in sutures was deficient. Skulls were small and disproportionate. Skeletons of Dhe/+ mice were hypomineralized and total body fat was deficient in males. In homozygotes, skin and oral mucosae were dysplastic and ulcerated. Nuclear morphometry of cultured cells revealed gene dose-dependent blebbing and wrinkling.

Conclusion

Dhe mice should provide a useful new model for investigations of the pathogenesis of laminopathies.

Acetabular revision with the Burch-Schnieder antiprotrusio cage and cancellous allograft bone

A retrospective review of 25 patients who underwent 28 acetabular revisions with the Burch-Schnieder antiprotrusio cage (Protek, Berne, Switzerland) and cancellous allograft bone was performed. Follow-up periods averaged 33 months. Patients had averaged 2.1 prior operations per hip. Twenty-two hips had American Academy of Orthopaedic Surgeons type III (combined segmental and cavitary bone loss) acetabular deficiency. Five hips had type II (cavitary bone loss) and one hip had type I (segmental bone loss) acetabular deficiency. After surgery, 80% of the patients had mild or no pain and 80% functioned as at least a community ambulator. Radiographic analysis included a detailed study of implant migration and the degree to which the hip center and bone stock were restored. Significant component migration was documented in 14% of the acetabular reconstructions. The hip center was improved from a preoperative side-to-side difference of 12.5 mm to 4.9 mm at final evaluation (P = .01). Average medial wall bone stock was improved from 1.9 mm before surgery to 10.1 mm postrevision (P < .01). No patients required revision of the antiprotrusio cage for problems related to the acetabular reconstruction. For failed acetabular components associated with moderate to massive bone loss, the antiprotrusio cage reliably reconstituted the hip joint center and acetabular bone stock. The short-term incidence of mechanical loosening parallels that of previously reported acetabular reconstruction techniques.