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One of the earliest events observed in the 'dedifferentiation phase' of traumatic regeneration is an in vivo increase in transcription. In order to see whether that increase corresponds to a variation at the level of genetic material, we prepared chromatin from normal and regenerating animals (12 h after amputation) for transcription in vitro by E. coli RNA polymerase. The template activity of regenerating chromatin was 2.1-fold higher than normal under standard conditions and showed an altered response to variation of the ionic strength of the medium. The accessibility of DNA in the chromatin was tested using mild digestion by DNAase II. Almost twice as much DNA was solubilised from regenerating chromatin as from normal chromatin. These data were correlated with morphological changes (decondensation) observed by electron microscopy.

A quantitative study of elementary granules in neuron axons of the nervous chain of Owenia fusiformis (Annelid polychaete) shows that daily variations of the number of secretory granules occur in unamputated animals and in ventral tissue cultures. These variations are correlated with the thythm of the cell cycle.

During anterior traumatic regeneration of the polychaete annelid Owenia fusiformis, we have observed by electron microscopy the dedifferentiation processes of muscle cells. The dedifferentiated cells are reminiscent of undifferentiated myoblasts. They form the blastema and redifferentiate in muscle cells in the regenerate. The in vivo and in vitro biochemical studies of the biosynthesis of contractile proteins, as markers of the terminal differentiation programme of the muscle cells, showed that gene expression correlated with the terminal differentiation programme (at last for muscle cells) seemed unaffected. It seems in fact that contractile protein synthesis is regulated partly at the translational level during traumatic regeneration in the invertebrate.

Amputation of the tail of the amphibian Pleurodeles waltlii leads to the formation of a blastema composed of undifferentiated cells during the first stages of regeneration. Between the 3rd and 4th week following amputation, the first fully differentiated striated muscle cells appear, and in the 6th week myogenic differentiation extends throughout the regenerate. Myoblasts appear in cell patches where cells fuse as differentiation proceeds. Using a cloned cDNA probe to a striated muscle actin gene specifically expressed in adult skeletal muscle, we show that no corresponding mRNA remains during dedifferentiation. A new actin transcript of the same length as cardiac actin transcript appears in the 4th week after amputation. We conclude that for the myogenic cell line, differentiation in the regenerate is accompanied by an actin isoform transition similar to that seen in embryonic terminal differentiation of higher vertebrates.

In a system consisting of synovial samples taken surgically and maintained in culture, the authors studied the regulation of enzyme synthesis by taking acid phosphatase as the test enzyme. By means of double labelling and the use of protein synthesis inhibitors, they were able to demonstrate that this synthesis was stimulated by the addition of rheumatoid factor to the culture medium and that it depended on the transcription activity of the genome and on the translation of the information molecules.

The binding of [3H] Uridine labelled RNAs and [32P] RNAs to poly U filters using the Sheldon et al. technique (1972) shows an increase in the poly A+ RNA populations from total RNAs and cytoplasmic RNAs in the prereplicative phase of the regenerating process in Owenia fusiformis. This increase confirms that the first stage of this process consists in an activation of the transcription of the genetic material concerning mainly mRNAs synthesis activation.

3H Trp and 14C Lys incorporation in proteins from chromatin of normal and regenerating animals, purified on metrizamide, show that the synthesis of these proteins is different in the two cases.

We have analysed DNA synthesis in early phases of regeneration in a marine Polychaete Annelid, Owenia fusiformis. The length and efficiency of the prereplicative phase was found to vary with the diurnal rhythm of activity of the animal; that is, it depends on the initial state of the cell population at the moment of the onset of proliferative stimulatin. When animals were operated on at 12 a.m., the duration of the prereplicative phase of the first cells stimulated to proliferate was found to be 12 h. The remaining cells entered the S-phase progressively in waves until the 3rd day following amputation when nearly 100% of the blastema cells were stimulated. At that time the cell-cycles of these dividing cells were found to be highly synchronized. Blastema differentiation takes place on the 4th day and is initiated by stomodeum formation. During the differentiation phase, DNA synthesis is restricted to small areas of the regenerating part. The system described is viewed as a new instrument for investigating the control of the cell cycle in synchronized and subsequently differentiating tissue cells.