Reversible inactivation of cell-type-specific regulatory and structural genes in migrating isolated striated muscle cells of jellyfish

We have investigated, by RT-PCR and in situ hybridization, expression of ge nes encoding regulatory and structural proteins in migrating mononucleated striated muscle cells of the medusa Podocoryne carnea. Expression of the th ree homeobox genes Otx, Cnox1-Pc, and Cnox3-Pc; a specific splice variant o f the myosin heavy chain gene (Myo1); and a tropomyosin (Tpm2) is stable in isolated and cultured striated muscle tissue. When grafted onto cell-free extracellular matrix (ECM), muscle cells of the tissue fragments leave thei r native ECM and migrate as a coherent tissue onto a host ECM until a stret ched cell monolayer is formed. Shortly after the first cells of the grafted isolate have made contact with the host ECM, Otx and Cnox1-Pc expression i s completely turned off in all cells of the graft, including those still ad hering to their native ECM. Myo1 message disappears with a delay while the expression level of Tpm2 is strongly reduced. However, expression of the ho meobox gene Cnox3-Pc, a msh-like gene, and of the ubiquitously expressed el ongation factor 1 alpha is not affected by the migration process. All genes are reexpressed after 12-24 h, once migration of the cells has ceased. Our results demonstrate that the first few migrating cells induce a change in gene expression which is rapidly communicated throughout the entire tissue. Furthermore, we showed that commitment of striated muscle cells remains st able despite the transient inactivation of cell-type-specific regulatory an d structural genes. (C) 1999 Academic Press.