Mosaic pattern of Cre recombinase expression in cochlear outer hair cells of the Brn3.1 Cre mouse.

Abstract

The Brn3.1 gene encodes for the protein Brn3.1, which is a member of the POU-IV class of transcription factors. Mutation leads to nonsyndromic human progressive hearing loss (DFNA15). To investigate the suitability of the Brn3.1 promoter for Cre recombinase-induced genetic recombination in cochlear hair cells, we established a transgenic Brn3.1 Cre mouse. This mouse line was crossbred with floxed ROSA26 and ROSA26 reporter mice. The cochleae were histologically analysed in cryosections at E16.5 and whole-mount preparations from P2 until P85. In addition, mice from all used strains and their recombinant offspring were tested electrophysiologically by auditory brainstem responses (ABR) and distorsion product otoacoustic emissions (DPOAE). Cre recombinase activity could be detected in P14 and P21 animals in a mosaic pattern in 26.3 and 9.9% of the outer hair cells, respectively. All investigated mice showed normal ABR and DPOAE values, indicating that neither insertion of the internal ribosome entry site (IRES) Cre cassette into the Brn3.1 gene led to abnormal auditory development nor did the reporter strains show inherited hearing disorders. This study shows that Cre expression under the control of the Brn3.1 promoter is feasible and that the insertion of the internal ribosome entry site Cre cassette into this locus exerted no effects on hearing development. Because of the inconstant pattern and the limited duration of expression, the application of the developed mouse line might be restricted. Also, the unchanged hearing capacity and structural integrity of the organ of Corti in available reporter lines indicate that they may be useful tools for hearing research.