BACKGROUND:Rapid development of spermatogonial stem cells is the new hope for assisting reproductive technologies,and the stability of the number and structure of the chromosome cultured in vitro is one of the important factors in usage.OBJECTIVE: To study the influential factors on G-band exhibition in mouse spermatogonial stem cells, so as to offer a technology to identify karyotype of stem cells in culture.DESIGN: Observational experiment.SETTING: Luzhou Medical College.MATERIALS: The experiment was conducted in the Laboratory of Medical Molecular Biology, Luzhou Medical College from March 2004 to April 2005. 10 days old male and female Kunming mice were provided by Department of Animal of Luzhou Medical College (number of license No. 17 of experimental animal quality administration in Sichuan province).There were low-sugar DMEM medium, 10 mg/L Mitomycin-C, IMDM medium, 1 ×10-5 mol/L colchicines (PBS allocation),7.5 mmol/L KCL, fixative (mixture glacial acetic acid with methanol in 1:3), Giemsa staining solution and 0.25% zymine.METHODS: Bone marrow was aspirated from the thigh bone of mouse for feeder layer cells preparation. Cells from the male mice testis of 7-8 days after birth were prepared and made into cell suspension. After adjusting the cell density to 3×105 L-1, they were inoculated into the feeder layer of bone marrow stromal cells. Cells were cultured at 37 ℃ in CO2 incubator containing CO2 of 0.05 volume fraction and 70% humidity. The proliferation groups of stem cells cultured 15-20 days were selected, stirred and spread, and then treated with colchicine for 4-6 hours. Cell suspension was collected,and then stained after hypotonic treatment. The cells whose chromosomes were dispersed well and in metaphase were selected, and number of chromosomes was counted, and then the morphology of chromosomes was observed.MAIN OUTCOME MEASURES: Culture of bone marrow stromal cells and spermatogonial stem cells and coloration and count of chromosomes.RESULTS: The karyotype of spermatogonial stem cells was the same as the body cells of normal mouse, which showed granule or rod-shape. Karyotype was 20 pairs, 40 bars. Three kinds of chromosome morphology could be observed under oil immersion lens. The first type was condensed, which could be counted in total, but the band could not be seen.The second type was chromatosome that spread completely in the center of equatorial plate and were in metaphase. In this phase, total numbers and band were seen clearly. Last type-chromosomes had already folded and moved towards two poles and concentrated gradually, the total number of chromosomes could be counted, but bending could not be seen clearly.CONCLUSION:Many factors can affect the karyotype of spermatogonial stem cells, including the phase of cell division,effect of hypotonic solution, diffusion of the cell when dropping slides, concentration of trypsin and digestion time, etc.