Identification of stem cell markers lgr5, lgr6 and sox9 in canine hair follicle and epidermal tumours

Evidence is accumulating that tumours are driven by cancer stem cells. We investigated the expression of three putative stem cell (SC) markers, Lgr5, Sox9, at both protein and mRNA level, and Lgr6 mRNA, in 43 canine hair follicles (HF) and 18 cutaneous epidermal tumors in order to examine the possible contribution of HF SCs in their development and progression. Fisher's exact test was applied to evaluate the significance of the gene and protein expression levels of the investigated molecules and their correlation with histopathological parameters and malignancy. Lgr5 immunolabelling was not detected in any of the tumours analyzed, despite positive staining in the surrounding HFs. The expression of Lgr6 and Lgr5 mRNA was observed in the majority of the cases. Sox9 was expressed in several tumours at both the protein and the mRNA levels. Sox9 positive cells were mainly present among the basaloid neoplastic cells of infundibular keratinizing acanthoma and of squamous cell carcinoma, and in some cases of basal cell carcinoma (BCC) and trichoblastoma. A statistically significant correlation was observed between lack of Sox9 protein expression and histologically assessed malignancy (P=0.0448). The presence of Sox9 positive cells in both epidermal and HF tumours suggests their involvement in the development of these tumours. Our results suggest that Sox9 might represent a marker of HF differentiation and its expression in BCCs might indicate a differentiation of these tumors along the line of the outer root sheath. A significant correlation was observed between absent/low Lgr5 mRNA levels and histologically assessed malignancy (P=0.0001), suggesting a possible transient function of the molecule in the development of the investigated tumors. The highest Lgr6 gene expression level was observed in the trichoblastoma cases, indicating a possible role of the molecule in the development of this type of tumour.