Investigating the expression profiles of cysteine string proteins (CSPs) in cochlear tissue

This study aims to explore the expression patterns of cysteine string protein alpha (CSPα) and cysteine string protein beta (CSPβ) in the mammalian inner ear, with an emphasis on their temporal dynamics during the developmental stages of C57BL/6 mice.

We utilized immunofluorescence staining to assess the localization and distribution of CSPα and CSPβ within the inner ears of C57BL/6 mice and miniature pigs. Additionally, this method facilitated the investigation of their temporal expression profiles.

In adult C57BL/6 mice and miniature pigs, CSPα and CSPβ were identified in the cytoplasm of inner hair cells and spiral ganglion cells, yet were absent in outer hair cells. Both proteins were found to colocalize with Ctbp2 on the basal side of the cytoplasm in inner hair cells' basilar membrane. Expression of CSPα was observed at the nerve fiber termini at the basilar membrane's base of inner and outer hair cells 10 days postnatally in C57BL/6 mice. Notably, expression of both CSPα and CSPβ in the cytoplasm of inner hair cells emerged on the 12th day post-birth, aligning with the timeline for registering cochlear potentials. The expression levels of both proteins increased with age, but were consistently absent in outer hair cells. Contrastingly, expression of CSPα and CSPβ was present in the cytoplasm of inner hair cells in miniature pigs as early as one day post-birth, yet remained absent in the three rows of outer hair cells.

CSPα and CSPβ exhibit predominant and specific expression in inner hair cells and spiral ganglion cells. A unique expression pattern was observed for CSPα, which was also present at the nerve fiber endings of both inner and outer hair cells. The developmental expression trajectory of CSPα and CSPβ in mouse inner hair cells is characterized by an initial absence, followed by a gradual increase. Moreover, the timing of expression onset between mice and miniature pigs indicates distinct temporal dynamics, suggesting a potential role in auditory development.