Promotion on the differentiation of retinal Müller cells into retinal ganglion cells by Brn-3b

AIM： To investigate the role of Brn-3b in differentiation process of stem cells derived from retinal Muller cells into the ganglion cell. METHODS： The passage culture method of Muller cells from retina of newborn Sprague Dawley rats was carried out by repeated incomplete pancreatic enzyme digestion method. The cells were detected by fluorescence- activated ceil sorter （FACS）, immunohistochemistry technology and reverse transcription-polymerase chain reaction （RT-PCR） to determine the purity. The third passage of cells was induced in the serum-free dedifferentiation medium. The expression of the specific markers Ki-67 and nestin of retinal stem cells was measured by RT-PCR and Western blot. The cell proliferation of retinal stem cells was detected by 5- Ethynyl-2＇-deoxyuridine （Edu） staining. The cells were randomly divided into 5 groups as follows： group A： Brn-3bsiRNA group; group B： Brn-3b control siRNA group; group C： pGC-Brn-3b-green fluorescent protein （GFP） group; group D： pGC-GFP group; group E： control group （without any handling）. The purified Muller cells were cultured for 3-7d, then, the percentage of ganglion cells was counted by immunofluorescence staining. RESULTS： FACS demonstrated the purity of retinal Muller cells was more 97.44%. A few spherical cell spheres appeared. Immunofluorescence staining showed that stem cells within the spheres were positive for retinal stem cell-specific markers nestin （red fluorescence, 92.94%±6.48%） and Ki-67 （green fluorescence, 85.96%± 6.04% ）. Meanwhile, RT-PCR analysis showed cell spheres in the culture to have expressed a battery of transcripts characteristic of stem cells such as nestin and Ki-67, which were absent in the Muller cells. Western blot analysis further confirmed the expression of nestin and Ki-67 in the cell spheres but not in the Muller cells. Edu staining showed most of the nuclei within the cell spheres were stained red （82.80%±6.65%）, suggesting the new cell spheres had the capacity for effective proliferation. The statistics result showed the difference between Brn-3bsiRNA group and Brn-3b control siRNA group or the control group was significant （F=15, P〈 0.05）, while the difference between Brn-3b control siRNA group or the control group was not statistically significant （P 〉0.05）. CONCLUSION： The repeated incomplete pancreatic enzyme digestion method is an efficient and practical method to purify retinal Muller cells. Retinal stem cells were successfully cloned in the dedifferentiational medium. Retinal Muller cells are accessible sources of retinal stem cells. Brn-3b is an important regulatory gene in stem cells differentiated into retinal ganglion cell.