Expression of the mouse Macf2 gene during inner ear development.
Plakins, a family of linker proteins that connect cytoskeletal elements to cellular junctions and the extracellular matrix, are primarily responsible for the mechanical properties of cells and tissues. They include desmoplakin, envoplakin, plectin, dystonin/BPAG1, and Kakapo. Mutations in plakins cause several skin, muscular and neurological disorders. Macrophins are a recently discovered subfamily of plakins with binding domains for actin, intermediate filaments and microtubules. Characteristic features of macrophins include variable actin binding domains, a central rod domain containing both plectin and spectrin repeats, and a C-terminus containing EF hands and GAS2/GAR22 domain. We have examined expression of mouse Macf2, encoding macrophin-2, in adult tissues and in the developing, neonatal, and mature inner ear by in situ hybridization. Northern blot analysis identified three large tissue-specific Macf2 transcripts: a 16-kb mRNA in skeletal muscle and heart, a 15-kb mRNA in brain, and a 9-kb mRNA in RNA from ovary plus uterus. In situ hybridization of the developing mouse inner ear indicated that Macf2 is expressed in the otocyst at day 12.5, in the sensory epithelium by embryonic day 16.5, and in both inner and outer hair cells by day 16.5. Macf2 is expressed in the bodies of both sensory and motor neurons in the central and peripheral nervous system, including the auditory pathway. The Macf2 protein could be involved in the regulation of cytoskeletal connections to cellular junctions and play an important structural role in organs, such as the inner ear, that are subjected to strong mechanical forces.