ジーンターゲティングによるヒト疾患モデルの作製とその応用
1999 年 9 巻 1 号 p. 53-59
詳細
1999 年 9 巻 1 号 p. 53-59
DFN3, an X-linked non-syndromic mixed deafness, is associated with mutations of BRAIN-4 (POU3F4) which encodes a POU transcription factor. The clinical hallmarks of DFN3 are a conductive hearing loss with perilymphatic gusher during surgery and progressive sensorineural deafness. We generated a mouse model of DFN3 by a targeting disruption of Brain-4 (Brn-4) and elucidated the pathology of deafness and the underlying mechanisms.
The hearing of mutant mice was assessed by auditory brainstem response (ABR) as compared with that of wild-type control mice. Wild-type mice (12W) exhibited normal ABR waveforms and thresholds (23±3dB SPL, n=9). Mice homozygous for Brn-4 deletion (12W) showed a significant elevation of ABR thresholds (90±5dB SPL, n=8). The middle ear including the ossicular chains of homozygous mutant mice appeared grossly normal, indicating that the deafness of Brn-4 deficient mice is unlikely to be conductive in origin. To further elucidate the site responsible for the deafness, the endocochlearpotential (EP) was measured through the cochlear lateral wall. The wild-type mice showed 101±9mV of the EP (n=9). On the other hand, the EP averaged 45±7mV (n=7) in homozygous mutant mice.
Electron microscopy revealed that suprastrial fibroblasts in mutant mice were lacking in irregular processes or plasma membrane outfoldings. The volume of the cytoplasm and the number of mitochondria were also decreased. Fibroblasts filling the area between the stria vascularis and bony otic capsule were devoid of processes of the cell or mitochondria. Extracellular fibrous strands were sparse in mutant mice as compared with those in wild mice. On the other hand, the organ of Corti, the spiral ganglion cells, and the stria vascularis are grossly normal appearance. Brn-4 message was intensively observed in the spiral ligament and suprastrial cells as well as the cochlear capsule using non-isotopic in situ hybridization.
These findings suggest that Brn-4 plays a critical role in the development of fibroblasts along the cochlear duct, contributing to the generation of the EP and the responsible site for DFN3.
