Characterization of SARG/CDT22 in Ocular Surface

Abstract

Abstract: : Purpose: Androgen plays an important role in ocular surface functions. Many ocular surface tissues, e.g., meibomian and lacrimal glands etc, are androgen target organs. We found that our previously cloned cDNA from the mouse cornea named cornea derived transcript–22 (CDT22) was identical to a human transcript named "specifically androgen regulated gene" (SARG). SARG gene is mapped to human chromosome 1q32. It spans 11 kb in human genome and consists of 4 exons and 3 introns. This study was to further investigate SARG/CDT22 gene structure and its expression in ocular surface tissues. Methods: Automate DNA sequencing was used to obtain the full–length cDNA sequence. DNA sequence search analysis was done via NCBI Blast analysis program. Northern blotting and in situ hybridizations were carried out to examine the CDT22 mRNA distribution in various adult mouse tissues. Western blotting and immunohistochemical analysis using anti–CDT22 antibody were performed to characterize its cellular location and tissue distribution. Results: The mouse cdt22 cDNA clone contains 2954 base pair with 161bp 5’–untranslated region, 1818bp central region encoding 606 amino acids, and 758 bp 3’–untranslated region. The mcdt22 sequence shares 97% homology with a Homo sapiens SARG mRNA (#AAR11484) isolated from a human prostate carcinoma cell line. The mouse cdt22 mRNA expresses in various epithelium–containing tissues, but not in the tissues without an epithelium such as the heart and the muscle. Interestingly, the mouse cdt22 mRNA is highly expressed by the testis but not by the female sex organs, i.e., the uterus and the ovary. The cdt22 is a 65 kD cytoplasmic protein. In the mouse, it is only expressed by the basal layers of the corneal epithelium but little in the limbus, and in the acinar cells of the meibomian gland. In the rabbit, it is expressed in the ductal epithelial cells. Conclusions: CDT22 and SARG are identical genes. The abundant expression of the mCDT–22 in epithelial basal layer of the cornea and lacrimal and meibomian glands suggest that this protein has a special function. Studies of this androgen responsive gene function may help elucidate the pathobiology of androgen–associated dry eye syndrome.

Keywords: lacrimal gland • cornea: epithelium • pathobiology