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


  • Constance A. Cardasis,

    1. Department of Anatomy, College of Physicians and Surgeons, Columbia University, New York, New York 10032
    Current affiliation:
    1. Department of Anatomy, Downstate Medical Center, Brooklyn, New York 11203
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    • This paper is based on a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Faculty of Pure Science, Columbia University.

  • George W. Cooper

    1. Department of Anatomy, College of Physicians and Surgeons, Columbia University, New York, New York 10032
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  • Supported in part by a grant of the Institute of General Medical Sciences, GM 15289.


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.