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First published online February 29, 2008
Journal of Experimental Biology 211, 837-843 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.014340

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Quantitative analysis of neonatal skeletal muscle functional improvement in the mouse

David S. Gokhin^1,2, Samuel R. Ward³, Shannon N. Bremner^1,2 and Richard L. Lieber^1,2,*

¹ Department of Bioengineering, University of California-San Diego and Veterans Affairs Medical Center, La Jolla, CA 92093, USA
² Department of Orthopaedic Surgery, University of California-San Diego and Veterans Affairs Medical Center, La Jolla, CA 92093, USA
³ Department of Radiology, University of California-San Diego and Veterans Affairs Medical Center, La Jolla, CA 92093, USA

View larger version (74K): [in this window] [in a new window]   Fig. 1. Photograph of the experimental apparatus for functional testing of mouse pup hindlimbs. In this example, a P1 hindlimb is secured. The tibialis anterior (TA) muscle and the approximate locations of the tibia and femur are indicated.

View larger version (77K): [in this window] [in a new window]   Fig. 2. Fluorescence microscopy of transverse tibialis anterior (TA) muscle sections at P1 (A,B) and P28 (C,D) using laminin immunohistochemistry for muscle fiber size measurement (A,C) and phalloidin staining for measurement of myofibrillar packing (B,D). Extensive muscle hypertrophy and accumulation of myofibrillar material is evident between P1 and P28. Arrows in B indicate examples of how immature muscle fibers typically begin to accumulate myofibrillar material first in the subsarcolemmal region and then inward toward the central axis of the cell. Image B is shown at a higher magnification for clarity. Postnatal time-courses of fiber size (E) and the fraction of the cross-sectional area occupied by contractile material (F) are also presented. *P<0.05 relative to the previous time-point.

View larger version (24K): [in this window] [in a new window]   Fig. 3. Postnatal time-course of whole body mass (A), three architectural parameters: muscle mass (B), fiber length (C) and physiological cross-sectional area (PCSA; D), and postnatal time-course of isometric stress (E). Muscle mass (F) and fiber length (G) were positively correlated with contractile function (mass: P<0.001, R2=0.52; fiber length: P<0.0001, R2=0.82), but PCSA (H) was uncorrelated (P>0.1, R2=0.06). *P<0.05 relative to the previous time-point.

View larger version (34K): [in this window] [in a new window]   Fig. 4. Postnatal time-course of expression of MyHC isoforms (A) and the influence of individual MyHC isoforms on isometric stress (B–G). Sample MyHC gels of P1 and P28 muscle are shown next to the legend in A. The embryonic (EMB), neonatal (NEO), and IIX and IIB mature isoforms were all significantly correlated with contractile function (P<0.001 for each, R2EMB=0.48, R2NEO=0.72, R2IIX=0.46, R2IIB=0.62), although NEO was the strongest predictor as determined by stepwise multiple regression. Neither isoform I nor IIA was significantly correlated with contractile function (P>0.05 for each, R2I=0.09, R2IIA=0.01). *P<0.05 relative to the previous time-point.

View larger version (16K): [in this window] [in a new window]   Fig. 5. Time-course of desmin levels postnatally (A) and its influence on isometric stress (B). Desmin levels were weakly but significantly correlated with contractile function (P<0.05, R2=0.11). *P<0.05 relative to the previous time-point.