Differential expression of epidermal growth factor receptor (EGFR) in stomach and diverticulum of Otocinclus affinis (Steindachner, 1877) as a potential element of the epithelium remodeling mechanism.

It is suggested that due to the several stomach modifications, Otocinculus affinis (dwarf sucking catfish) possess the ability to breathe air during hypoxia, however, the exact mechanism remains unknown. The aim of this study was detailed analysis of the expression of EGFR in the stomach and diverticulum of the O. affinis at the mRNA and protein levels together with the immunohistochemical localization of EGFR in these organs. The intensity of band fluorescence corresponding to the EGFR gene expression level is significantly higher in the stomach than in the diverticulum. Further, quantitative analysis of EGFR protein abundance also revealed its higher synthesis in the stomach than in the diverticulum and the immunohistochemistry method confirmed these results. As regional localization of respiratory function in gut air-breathing fishes seems to be connected with "morphological remodeling" of the epithelium of their gut, the present research demonstrated the potential efficiency of the O. affinis stomach as a respiratory organ. Having the potential possibility to create an air-blood barrier in the gastrointestinal tract allowing gas diffusion and respiration in hypoxic states seems to be very beneficial for these fish. It seems that facultative gut air breathing fish species are a relevant vertebrate model for high throughput screening, vascular biology and evolution.