N came from experiments employing the same in vivo system as we used here ?CB5083 web fibres from donor geneticallymodified wild type mice grafted into pre-irradiated muscles of dystrophin-deficient mdx nude mice [6]. Further studies showed that modulation of the host SMER-28 web muscle environment is an important requirement for successful donor satellite cell engraftment: not only does the host niche need to be preserved, but also endogenous satellite cells have to be impaired [45]. Such modulation, achieved by irradiating host muscles, permits aged host muscle to be regenerated by donor 11967625 satellite cells as well as young host muscle [7,47]. Myotoxins, such as BaCl2, notexin and cardiotoxin, have been widely used to cause muscle injury [48,49]. These destroy myofibres, but myofibre basal lamina, satellite cells, nerves and blood vessels are preserved [48]. In response to the muscle injury, endogenous satellite cells activate, proliferate, migrate and either repair injured fibres, or regenerate new fibres [50,51]; thus the contribution of transplanted donor cells in competition with efficient host-mediated muscle regeneration is negligible [45]. Among the myotoxins we tested, BaCl2 was the only one, when injected 3 days before cell grafting, that promoted significantly more donor-derived muscle formation than in the non-treated host muscles, even though donor muscle formation was 10 times less than in the irradiated grafted muscles [45]. We were therefore interested to see the effect of BaCl2 on grafted single fibres, bearing their complement of satellite cells. We clearly show that, in our model system, donor muscle formation derived from isolated donor myofibres grafted into in BaCl2-injured host mdx nude muscles is rare and insignificant. However, although they do not give rise to either muscle fibres, or other cell types, within BaCl2-treated host muscles, a donor single fibre stimulated host muscle hypertrophy. The number of fibres has not increased, but the diameter of the fibres has, leading to a significant increase in muscle weight. The effect of the grafted isolated fibre on the host muscle is therefore hypertrophy, not hyperplasia, as it is an increase in fibre size rather than number. Intriguingly, this donor fibre-mediated hypertrophic effect occurred without pre-injury of the host muscle with BaCl2, indicating that non-treated mdx nude muscles, which would beThe Hypertrophic Effect is Mediated by the Donor Fibre Rather than Donor Satellite CellsAs an isolated donor myofibre, bearing its complement of approximately 7 satellite cells [6], grafted into host muscle was able to mediate muscle hypertrophy, we wished to see whether satellite cells removed from their fibre were also capable of causing this effect. We therefore designed a series of experiments where either single fibres, or freshly-stripped satellite cells, were isolated from b-actin-Cre:R26NZG donor mice and grafted into BaCl2treated host mouse muscles. This enabled us to determine whether donor cells had given rise to cells other than skeletal muscle fibres or satellite cells, which might be promoting the host muscle hypertrophy. As a positive control, satellite cells were grafted in pre-irradiated muscles [45] and, as a negative control, BaCl2injured muscles were injected with DMEM (Figure 4A). Quantification of donor-derived muscle and donor-derived nuclei inside and outside myofibres showed that, as expected, fibre formation derived from donor satellite cells was robust in pre-irradi.N came from experiments employing the same in vivo system as we used here ?fibres from donor geneticallymodified wild type mice grafted into pre-irradiated muscles of dystrophin-deficient mdx nude mice [6]. Further studies showed that modulation of the host muscle environment is an important requirement for successful donor satellite cell engraftment: not only does the host niche need to be preserved, but also endogenous satellite cells have to be impaired [45]. Such modulation, achieved by irradiating host muscles, permits aged host muscle to be regenerated by donor 11967625 satellite cells as well as young host muscle [7,47]. Myotoxins, such as BaCl2, notexin and cardiotoxin, have been widely used to cause muscle injury [48,49]. These destroy myofibres, but myofibre basal lamina, satellite cells, nerves and blood vessels are preserved [48]. In response to the muscle injury, endogenous satellite cells activate, proliferate, migrate and either repair injured fibres, or regenerate new fibres [50,51]; thus the contribution of transplanted donor cells in competition with efficient host-mediated muscle regeneration is negligible [45]. Among the myotoxins we tested, BaCl2 was the only one, when injected 3 days before cell grafting, that promoted significantly more donor-derived muscle formation than in the non-treated host muscles, even though donor muscle formation was 10 times less than in the irradiated grafted muscles [45]. We were therefore interested to see the effect of BaCl2 on grafted single fibres, bearing their complement of satellite cells. We clearly show that, in our model system, donor muscle formation derived from isolated donor myofibres grafted into in BaCl2-injured host mdx nude muscles is rare and insignificant. However, although they do not give rise to either muscle fibres, or other cell types, within BaCl2-treated host muscles, a donor single fibre stimulated host muscle hypertrophy. The number of fibres has not increased, but the diameter of the fibres has, leading to a significant increase in muscle weight. The effect of the grafted isolated fibre on the host muscle is therefore hypertrophy, not hyperplasia, as it is an increase in fibre size rather than number. Intriguingly, this donor fibre-mediated hypertrophic effect occurred without pre-injury of the host muscle with BaCl2, indicating that non-treated mdx nude muscles, which would beThe Hypertrophic Effect is Mediated by the Donor Fibre Rather than Donor Satellite CellsAs an isolated donor myofibre, bearing its complement of approximately 7 satellite cells [6], grafted into host muscle was able to mediate muscle hypertrophy, we wished to see whether satellite cells removed from their fibre were also capable of causing this effect. We therefore designed a series of experiments where either single fibres, or freshly-stripped satellite cells, were isolated from b-actin-Cre:R26NZG donor mice and grafted into BaCl2treated host mouse muscles. This enabled us to determine whether donor cells had given rise to cells other than skeletal muscle fibres or satellite cells, which might be promoting the host muscle hypertrophy. As a positive control, satellite cells were grafted in pre-irradiated muscles [45] and, as a negative control, BaCl2injured muscles were injected with DMEM (Figure 4A). Quantification of donor-derived muscle and donor-derived nuclei inside and outside myofibres showed that, as expected, fibre formation derived from donor satellite cells was robust in pre-irradi.
