Presenting Author:
Satoe Homma, Ph.D.
Principal Investigator:
Jing Zheng, Ph.D.
Department:
Otolaryngology - Head and Neck Surgery
Keywords:
Cytoskeleton, Microtubule minus-end binding protein, CAMSAP3, Auditory system, Olfactory system, Cochlea, Olfactory sens... [Read full text]
Location:
Third Floor, Feinberg Pavilion, Northwestern Memorial Hospital
B130 - Basic Science
Microtubule-Minus-End Binding Protein CAMSAP3 Hypomorphs Exhibit Auditory and Olfactory Dysfunction.
Calmodulin-regulated-spectrin-associated protein 3 (CAMSAP3), also called Marshalin (Zheng et al., 2013), is a microtubule (MT)-minus-end binding protein associated with centrosomal-independent MTs. CAMSAP3 is widely expressed in different types of cells in almost every tissue, including the organ of Corti and spiral ganglion neurons of the auditory nerve. To study CAMSAP3 function(s), we obtained a transgenic mouse model for CAMSAP3, Camsap3tm1a, which was created in the C57BL/6N line as part of the Sanger Institute Mouse Genetics Project using the “knockout-first” conditional allele targeting strategy (Skarnes et al., 2011). Although our RT-PCR data show that CAMSAP3 transcripts are indeed decreased in homozygous Camsap3tm1a mice, CAMSAP3 protein is still found in Camsap3tm1a/C57BL/6N mice by Western blot. Hence, the Camsap3tm1a/C57BL/6N mouse model is likely hypomorphic for CAMSAP3 but not a functional null. Camsap3tm1a/C57BL/6N mice show increased mortality before weaning, reduced size, and infertility in both sexes. To overcome the low reproduction rate and small litter size on the original C57BL/6N background, we re-derived this line on FVB and CBA/CaJ murine backgrounds. Increased survival rates were indeed observed in both Camsap3tm1a/FVB and Camsap3tm1a/CBA/CaJ homozygotes. Homozygotes from both re-derived strains remained smaller than their wildtype littermates, and produce audible vocalizations or “chattering” in both sexes. Consistent with characterization of the original Camsap3tm1a/C57BL/6N animals (Steel et al., ARO, 2016), hearing impairment was also observed in Camsap3tm1a homozygotes; however, the degree of hearing loss was highly variable among individuals and on different strain backgrounds. We suspect such variation may be associated with the degree of “leakiness” of CAMSAP3 mRNA expression. Although the basal loss of outer hair cells (OHCs), and sometimes pillar cells, was observed in the cochlear samples from Camsap3tm1a/CBA/CaJ homozygotes, it is not clear why hearing impairment occurs at low-frequencies where no gross anatomical abnormalities were observed. Thus, generation of conditional knockouts to selectively influence cochlear expression is underway to specifically address the role of CAMSAP3 in audition. Although we only observed abnormal upturned snouts in a few Camsap3tm1a/CBA/CaJ homozygous mice, all Camsap3tm1a homozygotes, regardless of the sex, age, or strain background, failed a behavioral test that evaluates olfactory function. Anatomical examination revealed complete obstruction of the nasal passage, thinning of the epithelial layer, and degeneration of olfactory sensory neurons indicating that CAMSAP3 is indispensable for olfaction. Therefore, CAMSAP3 function appears to be differentially affected depending on the tissue examined. These results collectively underscore the importance of CAMSAP3 in peripheral sensory organs. This work is supported by NIDCD grants DC000089 and DC011813.
