Figure 1.

HMGA2 mRNA and HMGA2 protein are highly expressed in myoblasts and embryonic rhabdomyosarcoma cells. A, HMGA2 mRNA levels gradually drop during human myoblast differentiation. Eighty percent of confluent HSMMs were cultured in differentiation media for 4 days. mRNA samples were harvested at days 0, 3, and 4. RT-PCR was then conducted to quantify the level of HMGA2 mRNA. Data were normalized to GAPDH and 18S mRNAs. *, P < 0.05 versus mRNA level at day 0. B, HMGA2 expression is inversely correlated with myoblast terminal differentiation. Human myoblasts were grown to more than 80% confluence in proliferation media, and switched to differentiation media for 2 days. Cells were then fixed and stained for HMGA2 and myosin heavy chain (MHC). At this stage, 30% to 40% cells became terminally differentiated and expressed MHC (scale bar, 50 μm). Interestingly, HMGA2 and MHC expression were mutually exclusive. MHC-positive cells are negative for HMGA2 [white arrow, HMGA2(+)/MHC(−) nuclei; yellow arrow, HMGA2 (−)/MHC(+) nuclei]. C, HMGA2 mRNA is absent in adult human tissues but reactivated in various cancer cells. Rhabdomyosarcoma (RMS) shows the highest average expression level. ES, embryonic stem cells. D, HMGA2 mRNA is highly expressed in normal human myoblasts and rhabdomyosarcoma cells of the ERMS subtype. *, P < 0.05, Student t test. E, HMGA2 protein is selectively expressed in ERMS cell lines, whereas HMGA1 is ubiquitously expressed. N, nuclei; C, cytoplasmic. F HMGA2 protein is localized to the nuclei of normal human myoblasts and rhabdomyosarcoma cells. Scale bar, 25 μm. G HMGA2 is widely expressed in primary human ERMS specimens. Scale bar, 50 μm.