The level of expression and the appropriate regulation of the various chicken actin genes, when stably introduced into mouse myogenic cell lines, is dependent upon the developmental history of the particular line. The skeletal actin genes are not appropriately regulated in adult myogenic satellite cells, whereas correct regulation is observed in embryonically derived lines. The cytoplasmic beta actin down regulates during myogenesis in all muscle lines tested so far. These various lines were used to demonstrate that all the sequence information necessary for the regulated expression of the actin genes was present in our genomic isolates. Promotor constructs with the bacterial CAT gene have shown the transcriptional control and regulatory regions for cardiac actin are contained within the 300 bp 5' to the start of transcription. Transcription of the beta cytoplasmic actin is not directly regulated through the promotor region, as determined by promotor exchanges and CAT constructs. Deletion analysis has defined a 320 bp region spaning the polyadenylation signal that is responsible for the transcriptional regulation of beta actin. The promotor regions for the myosin LC1/LC3 gene have been defined with CAT constructs. Sequences involved in the regulated, tissue specific expression of these are also contained within these promotor regions. Two lower eukaryotic systems are under investigation: the cytoplasmic myosin gene of Acanthamoeba and the myosin gene of yeast. We have isolated and determined the nucleotide sequence of the Acanthamoeba gene and compared its structure and organization to other myosin genes. Using a probe from the myosin gene of C. elegans we have identified homologous sequences in the yeast genome. PC12 cells undergo neuronal differentiation in response to NGF. We have isolated a cDNA sequence and the corresponding gene that is induced 50-80 fold in response to NGF. The cDNA encodes a polypeptide of 72,000 daltons. We have made antibodies to different portions of the cDNA using Lac Z fusions to study the induction and localization of the protein. The promotor of the NGF induced gene responds to NGF when fused to CAT and transfected into PC12 cells.
