Genes specific to ES cells show increased expression in sphere cultures derived from bone sarcomas. (A) Monolayer and sarcosphere (SP) cultures initiated from five osteosarcoma (OS) and three chondrosarcoma (CS) biopsies were analyzed for the expression of Oct 3/4, Nanog, and STAT3 using semiquantitative RT-PCR. β-Actin expression was used as a positive control. Sphere cultures demonstrate increased transcription of both Oct 3/4 and Nanog over adherent cultures. STAT3 expression was uniform between both culture types. (B) Relative band intensities for Oct 3/4 and Nanog for each culture from (A) were quantitated by densitometry, normalized relative to β-actin, and plotted on the graph (Oct 3/4, x-axis; Nanog, y-axis). As indicated by the grouping, the sphere cultures of each sarcoma showed a significantly greater expression of both Oct 3/4 and Nanog than adherent cultures (P < .05, Pearson's correlation coefficient). (C) Western blot analysis of lysates from representative bone sarcoma cell cultures for the protein expression of Oct 3/4, STAT3, and activated (phosphorylated, p) STAT3. β-Actin was used as a positive control for loading, membrane transfer, and immunoblotting. All cultures showed positive staining of protein bands of appropriate sizes, as indicated. (D) Small (left) and large (right) sarcospheres were embedded in paraffin and stained using immunohistochemistry for Oct 3/4 and Nanog, as indicated. Small spheres show an intense staining of cells in the periphery (arrows). Large spheres show similar numbers of darkly staining cells (arrows), with dramatically increased numbers of poorly staining cells in the interior of the sphere.