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Modulation of contractile protein gene expression in fetal murine crural muscles: Emergence of muscle diversity
Author(s) -
Ontell Martin P.,
Sopper Maggie M.,
Lyons Gary,
Buckingham Margaret,
Ontell Marcia
Publication year - 1993
Publication title -
developmental dynamics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.634
H-Index - 141
eISSN - 1097-0177
pISSN - 1058-8388
DOI - 10.1002/aja.1001980306
Subject(s) - biology , myogenesis , in situ hybridization , myocyte , skeletal muscle , anatomy , myosin , fetus , messenger rna , myogenin , endocrinology , medicine , microbiology and biotechnology , gene , genetics , pregnancy
The modulation of contractile protein gene expression in mouse crural muscles (i.e., muscles located in the region between the knee and ankle) during the fetal period (defined as 15 days gestation to birth), resulting in diversity among and within these muscles, has been evaluated with in situ hybridization and correlated with morphogenetic events in the extensor digitorum longus and soleus muscles. During the fetal period extensive secondary myotube formation occurs in the crural muscles, and the myotubes become innervated (Ontell and Kozeka [1984a, b] Am. J. Anat. 171:133–148, 149–161; Ontell et al. [1988a, b] Am. J. Anat. 181:267–278, 181:278–288). At 15 days gestation, hybridization with 35 S‐labeled antisense cRNA probes demonstrates the accumulation of transcripts forα‐cardiac andα‐skeletal actin; MLC 1A , MLC 1F , and MLC 3F ; and MHC emb , MHC pn , and MHC β/slow . At 16 days gestation, accumulation of MHC emb transcripts is reduced (as compared with earlier developmental stages); intensity of signal following hybridization with the probe forα‐skeletal actin is, for the first time, equal to that for the cardiac isoform; and MLC 1V mRNA accumulation is discernible. At this stage, variation in transcript accumulation for some mRNAs among and within crural muscles becomes evident. Two factors may play a role in the selective distribution of these transcripts: (1) the stage of muscle maturation; and (2) the future myofiber type. At 16 days gestation anterior crural muscles (which mature ˜ 2 days before posterior crural muscles; Ontell and Kozeka [1984a, b], ibid., Ontell et al. [1988a, b], ibid.) exhibit a greater accumulation of transcripts forα‐skeletal actin and for MLC 3F than is found in posterior crural muscles. In muscles that in the neonate are composed, in large part, of slow myofibers, MHC β/slow and MLC 1V mRNAs accumulate in greater amounts, whereas MHC pn transcripts are less abundant in the soleus muscle than in other crural muscles. By 19 days gestation regionalization of transcript accumulation is more pronounced. The soleus muscle, a predominantly slow twitch muscle in the newborn mouse (Wirtz et al. [1983] J. Anat. 137:109–126) exhibits strong signal after hybridization with probes specific for MHC β/slow and MLC 1V . While the level of transcript accumulation for the developmetal isoforms, MHC emb , MLC 1A , andα‐cardiac actin, is greatly reduced in most crural muscles at 19 days gestation, these transcripts persist in the soleus muscle at levels equal to or exceeding their amount in limb muscles of 13 day gestation mouse embryos. By 19 days gestation both MyoD and myogenin are “down‐regulated” (as compared with their expression at earlier developmental stages) in all muscle masses. Alterations in contractile protein gene expression are correlated with changes in the myogenic regulatory factors present in fetal hindlimbs during development. © 1993 Wiley‐Liss, Inc.