An analysis of nuclear numbers in individual muscle fibers during differentiation and growth: A satellite cell‐muscle fiber growth unit

Abstract

A numerical analysis of changes in the populations of nuclei in individual, intact muscle fibers was made to study how multinucleation arises during normal differentiation and growth. Gastrocnemius muscle fibers from pre- and post-natal mice were isolated with guanidine (Cardasis and Cooper, '75) and examined. Satellite cells associated with muscle fibers were first observed at 19 days of gestation. The number of nuclei per muscle fiber (muscle + satellite cell nuclei) averages 83 at this age, 157 at birth and continues to increase to 354 by 63 days of age. However, the rate of increase during growth is not constant. Estimates of satellite cell and muscle nuclei in histological cross sections indicate that there is a decrease in the percentage of satellite cells from 32% at birth to 6% in the adult. However, the numbers of satellite cells associated with individual muscle fibers, calculated from these percentages and the nuclear counts on whole fibers, decreases only between 2 and 4 weeks of age. Cytosine arabinoside was injected subcutaneously during the first two weeks of age. Pairs of satellite cells, abnormal nuclei and elevated percentages of satellite cells were observed. This evidence as well as the numerical analysis of nuclear populations in whole fibers lends further support to the hypothesis that satellite cells account for the increase in muscle nuclei from birth to maturity.

Deletion of Pax7 changes the tunica muscularis of the mouse esophagus from an entirely striated into a mixed phenotype

“…The satellite cell frequency increased from nearly zero at E19 to ϳ24% at P4 in wild-type esophagi and declined subsequently to ϳ5% at 3 months. These percentages are in agreement with observations in limb skeletal muscle where satellite cells account for ϳ32% of sublaminal muscle nuclei followed by a drop to less than 5-6% in the adult (Cardasis and Cooper, 1975;Bischoff, 1994). This decline in satellite cell nuclei during postnatal muscle development further indicates in agreement with results in skeletal muscle (Bischoff, 1994), that satellite cells fuse into new growing myotubes/myofibers also in the esophagus increasing the number of myonuclei.…”

The methyl-CpG-binding protein CIBZ suppresses myogenic differentiation by directly inhibiting myogenin expression

“…The DNA-protein complex was resolved in a 6% polyacrylamide gel, and then electroblotted onto a Nylon membrane and UV-crosslinked. The blot was then blocked and incubated with anti-DIG antibody conjugated with alkaline phosphatase at room temperature for 30 min, washed, subjected to chemiluminescent detection with CSPD (disodium 3-(4-methoxyspiro{1,2-dioxetane-3,2′-(5′-chloro)tricyclo[3.3.1.1 3,7 ]decan}-4-yl)phenyl phosphate) as the substrate, and exposed to an X-ray film. CpG methylation of the probe was catalyzed by M.SssI as described above.…”

“…Adult skeletal muscle is capable of repeated self-repair, throughout life, in response to damage caused by injury or myopathies [1,2]. Such postnatal development and self-repair of skeletal muscles is mainly attributable to muscle progenitor cells called satellite cells, which are located between the basal lamina and the plasma membrane of muscle fibers [1,3]. Satellite cells account for about 30% of the muscle nuclei in neonatal mice, but decline to 2-6% in 2-month-old adults [3].…”

“…Such postnatal development and self-repair of skeletal muscles is mainly attributable to muscle progenitor cells called satellite cells, which are located between the basal lamina and the plasma membrane of muscle fibers [1,3]. Satellite cells account for about 30% of the muscle nuclei in neonatal mice, but decline to 2-6% in 2-month-old adults [3]. As adulthood is reached, the residual satellite cells become quiescent, but upon activation they divide to repopulate the satellite cell pool and to generate a large number of daughter myoblasts.…”

Postnatal overexpression of the CT GalNAc transferase inhibits muscular dystrophy in mdx mice without altering muscle growth or neuromuscular development: Evidence for a utrophin-independent mechanism

“…Here we show the percentage of centrally located myofiber nuclei because it is one the most robust pathology measures in mdx muscles. As normal myofibers mature, nuclei migrate out to the periphery of the myofiber, such that fewer than 5% remain in a central position [20][21][22][23]. However, if dystrophin-lacking muscles are damaged and undergo regeneration in the adult mouse, nuclei within the regenerated myofiber remain in a central position for most of the life of the animal.…”