Deletion of Limk1 and Limk2 in mice does not alter cochlear development or auditory function

Qiaojun Fang,Jian Wang,Yuan Zhang,Cheng Cheng,Ming Guan,Su-Hua Sha ,Kaiming Su,Dan Li,Renjie Chai,Zuhong He,Buwei Shao,Tian Wang,Menghui Liao,Jiaqi Guo,Peng Da,Xiaohan Wu,Yuhua Zhang,Zikai Zhou,Haolai Pan,Fangyi Chen

doi:10.1038/s41598-019-39769-z

Abstract

Inherited hearing loss is associated with gene mutations that result in sensory hair cell (HC) malfunction. HC structure is defined by the cytoskeleton, which is mainly composed of actin filaments and actin-binding partners. LIM motif-containing protein kinases (LIMKs) are the primary regulators of actin dynamics and consist of two members: LIMK1 and LIMK2. Actin arrangement is directly involved in the regulation of cytoskeletal structure and the maturation of synapses in the central nervous system, and LIMKs are involved in structural plasticity by controlling the activation of the actin depolymerization protein cofilin in the olfactory system and in the hippocampus. However, the expression pattern and the role of LIMKs in mouse cochlear development and synapse function also need to be further studied. We show here that the Limk genes are expressed in the mouse cochlea. We examined the morphology and the afferent synapse densities of HCs and measured the auditory function in Limk1 and Limk2 double knockout (DKO) mice. We found that the loss of Limk1 and Limk2 did not appear to affect the overall development of the cochlea, including the number of HCs and the structure of hair bundles. There were no significant differences in auditory thresholds between DKO mice and wild-type littermates. However, the expression of p-cofilin in the DKO mice was significantly decreased. Additionally, no significant differences were found in the number or distribution of ribbon synapses between the DKO and wild-type mice. In summary, our data suggest that the Limk genes play a different role in the development of the cochlea compared to their role in the central nervous system.

Highlights

The cochlea is the primary sensory organ in the inner ear for hearing
Confocal imaging of the whole-mount organ of Corti showed that LIMK1 was mainly expressed in the cytoplasm of hair cell (HC) and supporting cells (SCs) at postnatal day 21 (P21), while almost all of the LIMK2 was in the nuclei of HCs and SCs (Fig. 1a, Supplementary Fig. 2)
When looking at earlier time points, we found that the expression of LIMK2 was mainly in the cytoplasm at P3 but transferred into the nucleus during postnatal development (Fig. 2a)

Summary

Introduction

The cochlea is the primary sensory organ in the inner ear for hearing. There are two types of sensory hair cells (HCs) – inner hair cells (IHCs) and outer hair cells (OHCs) – and different supporting cells (SCs), including Deiters’ cells, pillar cells, Hensen’s cells, inner border cells, and inner phalangeal cells[1,2,3] (Supplementary Fig. 1). The electromotility of OHCs, which form the foundation for sound amplification in the cochlea, is largely dependent on the properties of prestin, which is a motor protein unique to mammals[13,14,15]. Abnormalities in the structure or function of HCs usually lead to hearing loss. The detailed expression pattern and the roles of Limk[1] and Limk[2] during the development of the mouse cochlea need to be further investigated. We report the expression pattern of LIMK1/2 in the mouse cochlea and the role of these proteins in auditory function and HC morphology in the mouse cochlea using a Limk[1] and Limk[2] double knock out (DKO) mouse model[33,34]

Methods

Results

Conclusion