Mouse bone marrow cells in suspension were separated into a number of fractions on the basis of cell density by equilibrium density gradient centrifugation, or on the basis of cell size by velocity sedimentation. After each type of separation, the cells from the various fractions were assayed for their ability to form macroscopic spleen colonies in irradiated recipient mice, and for their ability to form colonies in a cell culture system. The results from either separation technique demonstrate that cells in some fractions formed more colonies in vivo than in the culture system, while cells in other fractions formed more colonies in culture than in the spleen. The results of control experiments indicate that this separation of the two types of colonyforming cells was not a n artifact of the separation procedures. From these experiments it was concluded that the population of cells which form colonies in culture under the conditions used is not identical to the populaion of cells detected by the spleen colony assay.

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A young female was diagnosed as having X-linked muscular dystrophy of the Duchenne type. Chromosome studies, including trypsin-Giemsa banding, Quinacrine fluorescence, and nucleolus organizer region (NOR) silver staining revealed an X-autosome reciprocal translocation t(X;21) (p21;p12). Utilizing both [3H] thymidine autoradiography and the BrdU-Hoechst 33258-Giemsa technique, lymphocytes and fibroblasts were found to show a preferential inactivation of the normal X suggesting the presence of a single mutant gene on the translocated X. This patient is one of seven reported cases of an X-linked muscular dystrophy associated with an X-autosome translocation. In all seven cases the exchange point in the X chromosome is in band p21 at or near the site of the Duchenne gene.

The inhibitory effect of serum is one of the main obstacles less in primary human myoblasts. The lower transgene to the in vivo use of cationic liposomes as a DNA delivery expression in primary cells does not appear to be a result system. We have found that a novel liposome formulation, of less DNA uptake but might result from differences in DODAC:DOPE (1:1) is totally resistant to the inhibitory intracellular trafficking of the complexes. DODAC-based effects of serum for transfection of cultured myoblasts and liposomes are unique in their resistance to serum inhibition myotubes. Transfection with a lacZ reporter gene in the and may therefore be valuable for the systemic delivery of presence of 95% fetal bovine serum gave up to 25% ␤-genetic information to muscle and other tissues. gal-positive cells in C2C12 myoblasts and about six-fold