Isolation and purification of myotube and myoblast nuclei from cultures of embryonic chick skeletal muscle.

Methods are described for the preparation of purified myotubes from embryonic chick skeletal muscle cultures and the preparation of purified nuclei from both myotubes and myoblasts. Myotubes are released from the culture dish by digestion of their collagen substratum with collagenase, and purified by sucrose density gradient sedimentation. Nuclei are prepared from the isolated myotubes by controlled homogenization in Ca²⁺-free medium and sedimentation through 2.1 M sucrose. Nuclei are prepared from cultured myoblasts in a similar fashion, with the inclusion of the non-ionic detergent NP-40 in the homogenization medium and sedimentation through 2.4 M sucrose. Phase contrast microscopic examination showed that the nuclear preparations are free of visible cytoplasmic contamination, and are morphologically similar to nuclei observed in situ. Biochemical assays (protein/DNA and $\text{RNA}\text{DNA}$ ratios) confirm the purity of the nuclear preparations. Both nuclear preparations have been used to prepare purified chromatin which has spectral and chemical properties similar to those reported for chromatin purified directly from several chick tissues.