André Weydert

Developmental pattern of mouse skeletal myosin heavy chain gene transcripts in vivo and in vitro

We have studied the transcripts of the embryonic, perinatal, and adult fast myosin heavy chain (MHC) genes in mouse skeletal muscle in vivo before and after birth, and in vitro in myogenic cell lines. In vivo, in 15-day fetal muscle, embryonic and perinatal MHC mRNAs are both present, and the former is the major transcript. By 18 days the perinatal is predominant and the adult MHC mRNA appears. In beta-bungarotoxin-treated fetuses, a similar developmental pattern is detected, suggesting that it is nerve-independent and that primary myotubes alone undergo the same developmental changes. In vitro, in the absence of the nerve, embryonic, perinatal, and adult IIB MHC mRNAs accumulate. The level of the latter two isomRNAs is influenced by culture conditions.

Three linked myosin heavy chain genes clustered within 370 kb of each other show independent transcriptional and post-transcriptional regulation during differentiation of a mouse muscle cell line☆

We have examined myosin heavy chain gene transcription in the mouse muscle cell line C2/7 under different culture conditions. Gene-specific probes for embryonic (MHCemb), perinatal (MHCpn), and adult (MHCIIB) MHC sequences were used in nuclear run-on experiments, and transcriptional levels compared with cytoplasmic RNA accumulation of the transcripts during muscle cell differentiation. Transcripts are not detectable in myoblasts. These three MHC genes are physically linked within 370 kb of each other. However, they are not activated coordinately, but show independent transcriptional regulation as muscle cells differentiate into myotubes and as myotubes mature in culture. Post-transcriptional mechanisms also regulate cytoplasmic RNA accumulation of these MHC genes.

Changes in gene expression during myogenic differentiation: II. Identification of the proteins encoded by myotube-specific complementary DNA sequences☆

Abstract Changes in the pattern of protein synthesis during terminal differentiation of a mouse, myogenic cell line have been examined by two-dimensional gel analysis. In addition the the increase in messenger RNAs coding for the major contractile proteins, several other new proteins are expressed after cell fusion, together with the diminution or loss of proteins expressed in mononucleate cells. In the accompanying paper (Affara et al. , 1980), analysis of rnRNA changes using fractionated complementary DNA probes showed that a new group of mRNAs enters the polysomes after cell fusion. To identify which proteins are coded by mRNAs represented in this myotube-specific complementary DNA, we have vised a combination of in vitro translation and sulphydryl chromatography. The results indicate a correspondence between many of the new proteins appearing after cell fusion and the mRNAs encoded by myotube-specific complementary DNA sequences. Included amongst these proteins are some of the contractile polypeptides.

The Actin and Myosin Multigene Families

The Actin and Myosin Multigene Families: a) a study of the accumulation of their RNA transcripts demonstrates different developmental strategies during skeletal muscle formation, b) a genetic analysis of their chromosomal organization indicates gene dispersion and permits some precise localizations on the genetic map of the mouse.

From Grenoble to Grenoble (1972–2000): Limb development and regeneration revisited

Culminating in the 60s and 70s, there was a flourishing school of developmental biology in Grenoble, France, dealing with limb development and led by Madeleine Kieny. In 1972, Madeleine Kieny launched the first International Limb Conference. Limb meetings have then been moving around the world at a more or less regular pace. Since 1996, however, the meeting has been held every second year, testifying of the renewed interest in limb development as a paradigm to investigate morphogenetic mechanisms. For the 28th anniversary of its foundation, the meeting was back in France, near Grenoble, in the tiny village of Aussois at the gateway to the Alps’ natural park of Vanoise. John Saunders (1),* in a vivid opening lecture, reminded us of what we owe to the experimental embryologists and particularly emphasized the contributions of Madeleine Kieny and of Rodolfo Amprino. As has been the rule for the last meetings, all prominent aspects of limb development were treated, i.e., initiation, patterning, differentiation and apoptosis, regeneration, evolution and clinical aspects in human. We outline here what we feel were the most characteristic outcomes of the 2000 meeting.

Actin and Myosin Genes and Their Expression During Skeletal Muscle Myogenesis

The differentiation of skeletal muscle cells is characterized morphologically by the fusion of myoblasts to form multinucleated muscle fibres. This process takes place gradually during skeletal muscle development in vivo. It can also be followed in tissue culture. Mammalian myoblasts will grow in monolayers, either in primary culture or as established cell lines, and will fuse spontaneously when the culture becomes confluent (for review see Yaffe 1968, Buckingham 1977). The formation of muscle fibres is characterized biochemically by the increased synthesis of contractile proteins (e.g. Devlin and Emerson 1978, Garreis 1979) and their organization into sarcomeric structures (Fischman 1970), by the accumulation of enzymes important in muscle metabolism (e.g. Caravatti et al. 1979), and by the appearance of membrane components such as the acetylcholine receptor (e.g. Merlie et al. 1975), essential for nerve-muscle interaction.