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Dynamics of muscle fibre growth during postnatal mouse development.

White RB, Biérinx AS, Gnocchi VF, Zammit PS - BMC Dev. Biol. (2010)

Bottom Line: We found that there was no net gain in myofibre number in the EDL between P7 and P56 (adulthood).There was no further addition of myonuclei from P21, but myofibre volume continued to increase, resulting in an estimated approximately 3-fold expansion of the myonuclear domain to 26.5 x 103 microm3 by P56.Satellite cell numbers are initially stable, but then decrease to reach the adult level by P21.

View Article: PubMed Central - HTML - PubMed

Affiliation: King's College London, Randall Division of Cell and Molecular Biophysics, Guy's Campus, London SE1 1UL, UK.

ABSTRACT

Background: Postnatal growth in mouse is rapid, with total skeletal muscle mass increasing several-fold in the first few weeks. Muscle growth can be achieved by either an increase in muscle fibre number or an increase in the size of individual myofibres, or a combination of both. Where myofibre hypertrophy during growth requires the addition of new myonuclei, these are supplied by muscle satellite cells, the resident stem cells of skeletal muscle.

Results: Here, we report on the dynamics of postnatal myofibre growth in the mouse extensor digitorum longus (EDL) muscle, which is essentially composed of fast type II fibres in adult. We found that there was no net gain in myofibre number in the EDL between P7 and P56 (adulthood). However, myofibre cross-sectional area increased by 7.6-fold, and length by 1.9-fold between these ages, resulting in an increase in total myofibre volume of 14.1-fold: showing the extent of myofibre hypertrophy during the postnatal period. To determine how the number of myonuclei changes during this period of intense muscle fibre hypertrophy, we used two complementary mouse models: 3F-nlacZ-E mice express nlacZ only in myonuclei, while Myf5nlacZ/+ mice have beta-galactosidase activity in satellite cells. There was a approximately 5-fold increase in myonuclear number per myofibre between P3 and P21. Thus myofibre hypertrophy is initially accompanied by a significant addition of myonuclei. Despite this, the estimated myonuclear domain still doubled between P7 and P21 to 9.2 x 103 microm3. There was no further addition of myonuclei from P21, but myofibre volume continued to increase, resulting in an estimated approximately 3-fold expansion of the myonuclear domain to 26.5 x 103 microm3 by P56. We also used our two mouse models to determine the number of satellite cells per myofibre during postnatal growth. Satellite cell number in EDL was initially approximately 14 satellite cells per myofibre at P7, but then fell to reach the adult level of approximately 5 by P21.

Conclusions: Postnatal fast muscle fibre type growth is divided into distinct phases in mouse EDL: myofibre hypertrophy is initially supported by a rapid increase in the number of myonuclei, but nuclear addition stops around P21. Since the significant myofibre hypertrophy from P21 to adulthood occurs without the net addition of new myonuclei, a considerable expansion of the myonuclear domain results. Satellite cell numbers are initially stable, but then decrease to reach the adult level by P21. Thus the adult number of both myonuclei and satellite cells is already established by three weeks of postnatal growth in mouse.

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EDL myofibres from growing and adult mice. Entire EDL muscles from P3, P7 (a), P14, P21 and P56 (b) Myf5nlacZ/+ mice were cryosectioned and mid-belly sections stained with haematoxylin and eosin to determine total myofibre content and myofibre cross-sectional area. EDL myofibres were isolated from 3F-nlacZ-E mice at P3 (c), P7 (d), P14 (e), P21 (f) and P56 (g), fixed and incubated in X-gal solution to reveal the β-galactosidase activity of myonuclei by the presence of the blue reaction product. Images of representative myofibres were all taken at the same magnification and show that there is a 4.5-fold increase in length between P3 and adulthood (P56). Myonuclei appear to be uniformly distributed along the length of a myofibre at each age examined (c-g). Scale bar equals 100 μm for (a and b) and 1000 μm for (c-g).
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Figure 1: EDL myofibres from growing and adult mice. Entire EDL muscles from P3, P7 (a), P14, P21 and P56 (b) Myf5nlacZ/+ mice were cryosectioned and mid-belly sections stained with haematoxylin and eosin to determine total myofibre content and myofibre cross-sectional area. EDL myofibres were isolated from 3F-nlacZ-E mice at P3 (c), P7 (d), P14 (e), P21 (f) and P56 (g), fixed and incubated in X-gal solution to reveal the β-galactosidase activity of myonuclei by the presence of the blue reaction product. Images of representative myofibres were all taken at the same magnification and show that there is a 4.5-fold increase in length between P3 and adulthood (P56). Myonuclei appear to be uniformly distributed along the length of a myofibre at each age examined (c-g). Scale bar equals 100 μm for (a and b) and 1000 μm for (c-g).

Mentions: Muscle growth can be achieved by an increase in myofibre number and/or an expansion of individual myofibres. To first examine if hyperplasia of the EDL contributed to muscle growth during the postnatal period in mouse, we counted the number of myofibres contained in the mid-belly section of muscles dissected from P7, P14, P21 and P56 (adulthood) mice on haematoxylin and eosin stained (Figure 1a and 1b), or laminin-immunostained, cryosections (Table 1). This analysis showed that there was no change in EDL myofibre number between P7 and P56 (Table 1) (ANOVA: F = 1.0; p = 0.42 - the fall between 3 and 8 weeks is not significant, ANOVA with Tukey HSD post hoc testing: p = 0.50).


Dynamics of muscle fibre growth during postnatal mouse development.

White RB, Biérinx AS, Gnocchi VF, Zammit PS - BMC Dev. Biol. (2010)

EDL myofibres from growing and adult mice. Entire EDL muscles from P3, P7 (a), P14, P21 and P56 (b) Myf5nlacZ/+ mice were cryosectioned and mid-belly sections stained with haematoxylin and eosin to determine total myofibre content and myofibre cross-sectional area. EDL myofibres were isolated from 3F-nlacZ-E mice at P3 (c), P7 (d), P14 (e), P21 (f) and P56 (g), fixed and incubated in X-gal solution to reveal the β-galactosidase activity of myonuclei by the presence of the blue reaction product. Images of representative myofibres were all taken at the same magnification and show that there is a 4.5-fold increase in length between P3 and adulthood (P56). Myonuclei appear to be uniformly distributed along the length of a myofibre at each age examined (c-g). Scale bar equals 100 μm for (a and b) and 1000 μm for (c-g).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2836990&req=5

Figure 1: EDL myofibres from growing and adult mice. Entire EDL muscles from P3, P7 (a), P14, P21 and P56 (b) Myf5nlacZ/+ mice were cryosectioned and mid-belly sections stained with haematoxylin and eosin to determine total myofibre content and myofibre cross-sectional area. EDL myofibres were isolated from 3F-nlacZ-E mice at P3 (c), P7 (d), P14 (e), P21 (f) and P56 (g), fixed and incubated in X-gal solution to reveal the β-galactosidase activity of myonuclei by the presence of the blue reaction product. Images of representative myofibres were all taken at the same magnification and show that there is a 4.5-fold increase in length between P3 and adulthood (P56). Myonuclei appear to be uniformly distributed along the length of a myofibre at each age examined (c-g). Scale bar equals 100 μm for (a and b) and 1000 μm for (c-g).
Mentions: Muscle growth can be achieved by an increase in myofibre number and/or an expansion of individual myofibres. To first examine if hyperplasia of the EDL contributed to muscle growth during the postnatal period in mouse, we counted the number of myofibres contained in the mid-belly section of muscles dissected from P7, P14, P21 and P56 (adulthood) mice on haematoxylin and eosin stained (Figure 1a and 1b), or laminin-immunostained, cryosections (Table 1). This analysis showed that there was no change in EDL myofibre number between P7 and P56 (Table 1) (ANOVA: F = 1.0; p = 0.42 - the fall between 3 and 8 weeks is not significant, ANOVA with Tukey HSD post hoc testing: p = 0.50).

Bottom Line: We found that there was no net gain in myofibre number in the EDL between P7 and P56 (adulthood).There was no further addition of myonuclei from P21, but myofibre volume continued to increase, resulting in an estimated approximately 3-fold expansion of the myonuclear domain to 26.5 x 103 microm3 by P56.Satellite cell numbers are initially stable, but then decrease to reach the adult level by P21.

View Article: PubMed Central - HTML - PubMed

Affiliation: King's College London, Randall Division of Cell and Molecular Biophysics, Guy's Campus, London SE1 1UL, UK.

ABSTRACT

Background: Postnatal growth in mouse is rapid, with total skeletal muscle mass increasing several-fold in the first few weeks. Muscle growth can be achieved by either an increase in muscle fibre number or an increase in the size of individual myofibres, or a combination of both. Where myofibre hypertrophy during growth requires the addition of new myonuclei, these are supplied by muscle satellite cells, the resident stem cells of skeletal muscle.

Results: Here, we report on the dynamics of postnatal myofibre growth in the mouse extensor digitorum longus (EDL) muscle, which is essentially composed of fast type II fibres in adult. We found that there was no net gain in myofibre number in the EDL between P7 and P56 (adulthood). However, myofibre cross-sectional area increased by 7.6-fold, and length by 1.9-fold between these ages, resulting in an increase in total myofibre volume of 14.1-fold: showing the extent of myofibre hypertrophy during the postnatal period. To determine how the number of myonuclei changes during this period of intense muscle fibre hypertrophy, we used two complementary mouse models: 3F-nlacZ-E mice express nlacZ only in myonuclei, while Myf5nlacZ/+ mice have beta-galactosidase activity in satellite cells. There was a approximately 5-fold increase in myonuclear number per myofibre between P3 and P21. Thus myofibre hypertrophy is initially accompanied by a significant addition of myonuclei. Despite this, the estimated myonuclear domain still doubled between P7 and P21 to 9.2 x 103 microm3. There was no further addition of myonuclei from P21, but myofibre volume continued to increase, resulting in an estimated approximately 3-fold expansion of the myonuclear domain to 26.5 x 103 microm3 by P56. We also used our two mouse models to determine the number of satellite cells per myofibre during postnatal growth. Satellite cell number in EDL was initially approximately 14 satellite cells per myofibre at P7, but then fell to reach the adult level of approximately 5 by P21.

Conclusions: Postnatal fast muscle fibre type growth is divided into distinct phases in mouse EDL: myofibre hypertrophy is initially supported by a rapid increase in the number of myonuclei, but nuclear addition stops around P21. Since the significant myofibre hypertrophy from P21 to adulthood occurs without the net addition of new myonuclei, a considerable expansion of the myonuclear domain results. Satellite cell numbers are initially stable, but then decrease to reach the adult level by P21. Thus the adult number of both myonuclei and satellite cells is already established by three weeks of postnatal growth in mouse.

Show MeSH
Related in: MedlinePlus