Abstract Interferon inhibits multiplication of murine leukemia L1210 cells and the effect is evident 18 h after subcultivation. At this time a significant decrease in the synthesis of total RNA and protein was observed in interferon‐treated cultures compared to control cultures. Likewise, the formation of polyribosomes was inhibited in interferon‐treated cultures although no effect was observed on the formation of the ribosomal subunits. As control cells and interferon‐treated cells continued to multiply and the cultures attained cell density saturation, the differences in macromolecular synthesis and polyribosome formation between the cultures became less marked. Confidence that interferon itself was responsible for the effects observed stemmed from the use of highly purified interferon preparations and the availability, as a cell control, of a subline of L1210 cells resistant to interferon action. The possibility that a single mechanism of action is common to the antiviral effect of interferon and its effect on cell division is discussed.
Abstract Myoblast migration requires matrix metalloproteinase (MMP) activity but the contribution of individual MMPs or tissue inhibitors of matrix metalloproteinase (TIMPs), particularly MMP‐9 and TIMP‐1, is lacking. Using two clones derived for differential regulation of MMP‐2, MMP‐9, and TIMP‐1, we correlated protein expression with cell migration. MMP/TIMP regulation was determined by zymography, western blots, and quantitative reverse transcriptase–polymerase chain reaction (qRT‐PCR). Cell migration was compared in vitro and after grafting into nude – mdx mouse muscles. C2M9 clones produced high MMP‐9 and low MMP‐2, and migrated better than C2F clones, which secreted low MMP‐9, but overexpressed MMP‐2 and TIMP‐1. Improvement of C2F invasion by MMP‐9 and inhibition of C2M9 migration by MMP‐9 inhibitor I confirmed the role of MMP‐9 and pointed to potential inhibition by TIMP‐1. Higher complementation achieved by C2M9 grafts corroborated the beneficial effect of MMP‐9 overexpression. Modulation of MMP‐9 expression opens perspectives for improved efficacy of cell therapy for muscular dystrophies. Muscle Nerve, 2010
The chicken beta tropomyosin gene contains two sets of alternatively spliced, mutually exclusive exons whose utilization is developmentally regulated. Exons 6A and 6B are used in nonmuscle cells (or undifferentiated muscle cells) and skeletal muscle cells, respectively. A complex arrangement of cis-acting sequence elements is involved in alternative splicing regulation. We have performed an extensive mutational analysis on the sequence spanning the region from exon 6A to the constitutive exon 7. A large number of mutant minigenes have been tested in transfection assays of cultured myogenic cells, and the splicing products have been analyzed by cDNA polymerase chain reaction. We demonstrate that in undifferentiated myoblasts, exon 6B is skipped as a result of a negative control on its selection, while exon 6A is spliced as a default choice. We provide evidence that the focal point of such a regulation is localized in the intron upstream of exon 6B and probably involves the blockage of its associated branch point. In differentiated myotubes, in contrast, both exons are accessible to the splicing machinery. We show that the preferential choice of exon 6B in this splicing environment depends on the existence of a competition between the two exons for the flanking constitutive splice sites. We demonstrate that both the donors and the branch points of the two exons are involved in this competition.
Islet-1 expression identifies populations of progenitor cells in embryonic, fetal, and newborn murine hearts that are able to give rise to all cardiac cell lineages ex vivo and in vivo. Using systematic immunohistochemistry, we investigated whether islet-1-positive cells are present in adult mouse heart from the perspective of their potential therapeutic utility. The presence, localization, and nature of islet-1-positive cells were assessed in mice of different strains, ages, and conditions. Islet-1-positive cells were present in mouse heart from postnatal day 1 to young adulthood. Depending on the strain, these cells were organized in either 1 or 2 types of clusters localized to restricted areas, at a distance of 6%-35% of the heart length from the base. The first type of cluster was present in all strains and consisted of neural crest-derived cells that formed cardiac ganglia. The number of cells remained stable (a few hundred) from neonatal up to adult ages, and variations were noted between strains regarding their long-term persistency. The second type of cluster was essentially present in 129SvJ or Balb/C strains and absent from the other strains tested (C57BL/6J, C3H, SJL). It consisted of cells expressing highly ordered sarcomeric actin, consistent with their having cardiomyocyte identity. These cells disappeared in animals older than 4 months. Neither the number nor the type of islet-1-positive cells varied with time in a mouse model of dilated cardiomyopathy. Our studies demonstrate that islet-1-positive cells are relatively few in number in adult murine heart, being localized in restricted and rather inaccessible areas, and can represent both neural crest and cardiomyocyte lineages.
Fibroblastes de peau d'embryons de caille infectes par la souche virale incubes a 36 ou 41°C. Limitation, a 41°C, du nombre de divisions effectuees par ces cellules en infection primaire
