Real-time quantification of Xeroderma pigmentosum mRNA from the mammalian cochlea.
OBJECTIVE
Human mutations in the DNA repair genes, Xeroderma pigmentosum (XP)-C and XPA result in hearing loss, which has fueled the hypothesis that there is a significant demand for these genes in protecting cochlear genetic material. Therefore, we quantified the level of XPC and XPA mRNA in the mammalian cochlea.


METHODS
XPC and XPA mRNAs were purified from the cochlea of 15 Fischer344 rats and quantified using SYBR Green chemistry. Another 15 Fischer344 rats were sacrificed for immunolocalization of XPC and XPA polypeptides in the cochlea and kidney (control organ).


RESULTS
XP mRNA levels were up to 95% (XPA) and 69% (XPC) of the respective maximum expression capacity of each gene. In addition, these cochlear levels were up to sixfold (XPC) and threefold (XPA) greater than that of the kidney, which is known to exhibit XP-DNA repair activity that is greater than most organs of the body. Immunohistochemistry revealed that most kidney and cochlear cells were immunopositive.


CONCLUSIONS
These data suggest that under normal conditions the cochlea is experiencing persistent genomic stress that helps to explain the hypersensitivity of the cochlea to exogenous stressors (ototoxic xenobiotics and/or acoustic-overexposure) as well as provide a basis to interpret hearing loss among patients with XP.
Guthrie
O'neil W
OW
Department of Biology, Developmental, Cell and Molecular Biology Group, Duke University, French Science Research Center, Durham, North Carolina, USA. Oneil.Guthrie@va.gov
Carrero-Martínez
Franklin A
FA
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D003051:Cochlea / Q000502:physiology*; D004260:DNA Repair / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney / Q000502:physiology; D008322:Mammals; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; C554673:XPA protein, rat; C534808:XPC protein, rat