Figure 2

Structure and expression of the mef2A gene. Panel A. RNAs were isolated from AX4 cells during growth (0) or after development (2–24 hours). Expression of mef2A or the large mitochondrial rRNA (internal control), were determined by PCR. Panel B. RNA purified from AX4 cells developed for 8 hours was converted into cDNA, and the 5^′ end extended using an oligonucleotide complementary to nucleotides 145 to 164 of the gene. Two different amplification products were obtained and their nucleotide sequences aligned to the genomic DNA. A diagram of the deduced structure of the gene is shown. Exon sequences are indicated as boxes, blue boxes for untranslated regions and deep red boxes for translated regions. Arrows indicate transcription initiation sites. The sequence has been numbered from the A of the translation initiation codon. The location of intron/exon borders is indicated on the lower part of the diagram and that of transcription initiation sites in the upper part. The DNA fragment deleted in the mutant strains is indicated in the lower part of the diagram. Panel C. The activity of the mef2A promoter regions was studied using lacZ reporter vectors driving the expression of a short-lived form of β-galactosidase. The region from the 3^′ end of the closest upstream gene (−2201) to the end of exon 1 (−489) (Pr1) and from the end of exon 1 (−511) to exon 3 (164) (Pr2), or the complete promoter region (−2201 to 164) (cPr), were cloned. lacZ expression was analyzed by histochemistry, using the Xgal substrate (2 hours of incubation) in aggregates (10 hours of development), finger (16 hours), slug (24 hours of development under migration conditions), Mexican hat (18 hours) and culminant (22 hours) structures. Pictures were taken using a Leica stereomicroscope, after counter-staining with eosin. Scale bar: 0.2 mm.