Effects of divalent cations on M-cadherin expression and distribution during primary rat myogenesis in vitro.
In the process of myogenesis, cadherins are thought to be involved in the initial cell-cell recognition and possible initiation of myoblast fusion to form multinucleated myotubes. Of the cadherins, M-cadherin, but not N-cadherin, is down-regulated upon inhibition of myogenesis, suggesting that M-cadherin may be a key receptor involved in myogenesis. M-cadherin binds in a calcium-dependent manner, and depletion of divalent cations inhibits myoblast fusion. We analyzed the regulation of M-cadherin protein and mRNA levels in primary rat myogenic cultures in the presence and absence of divalent cations. In untreated cultures M-cadherin was localized to various myogenic cell-cell contacts. M-cadherin protein and mRNA levels showed a peak at day 2 after the initiation of growth. When divalent cations were removed from the cell culture medium, myoblast fusion was inhibited and immunocytochemical analysis revealed a failure of M-cadherin to localize to cell-cell contacts. Analysis of M-cadherin protein and mRNA in fusion-inhibited cultures still revealed a peak at day 2. However, by day 3, M-cadherin protein levels in the fusion-inhibited cultures were reduced in both the detergent-soluble and -insoluble fractions in comparison with the untreated cultures. Interestingly, beta-catenin, a protein associated with cadherins, was frequently observed at intercellular contacts in the fusion-inhibited cultures. We could also show that the intracellular levels of beta-catenin protein remained constant regardless of the presence or absence of divalent cations. In summary, the dynamic regulation of M-cadherin in muscle-fusion-related events is an indication of the importance of M-cadherin for myoblast fusion and myogenic differentiation.
Eng
H
H
Department of Cell and Molecular Biology, Karolinska Institute, Stockholm, Sweden.
Herrenknecht
K
K
Semb
H
H
Starzinski-Powitz
A
A
Ringertz
N
N
Gullberg
D
D
D000818:Animals; D015820:Cadherins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002412:Cations / Q000378:metabolism / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D017403:In Situ Hybridization; D018482:Muscle, Skeletal / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013848:Thigh / Q000196:embryology
D015820:Cadherins; D002412:Cations; D012333:RNA, Messenger; C070896:M-cadherin