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Mech Dev
1999 Sep 01;871-2:199-202. doi: 10.1016/s0925-4773(99)00148-3.
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Two skeletal alpha-tropomyosin transcripts with distinct 3'UTR have different temporal and spatial patterns of expression in the striated muscle lineages of Xenopus laevis.
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The Xenopus laevis alpha-tropomyosin (TM) gene, like its vertebrates counterparts, encodes muscle and non-muscle isoforms through two promoters and alternatively spliced exons. In the present study we describe a cDNA clone (XTMalpha7) encoding a skeletal muscle isoform of the gene that differs from the previously described skeletal TM transcript (XTMalpha2) by its 3'UTR sequence. The two skeletal alpha-TM encoding mRNAs are generated through distinct 3'end processing using different polyA signals and distinct patterns of exon splicing. Using RNAse protection and RNA in situ hybridization, we have analysed the developmental and spatial expression of the two transcripts. Both are expressed in the embryo, but XTMalpha7 is by far the most prevalent of the two. In contrast, only XTMalpha2 is expressed in adult striated muscle tissues. In the embryo, the spatial expression of XTMalpha7 is restricted to the somites whereas XTMalpha2 is expressed in both somites and embryonic heart.
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10495287
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Fig. 1. XTMa2 and XTMa7 cDNA sequence alignment, schematic structure of the Xenopus laevis a-TM 3' genomic region and expression of the two transcripts in adult striated tissues. (A) Sequence alignment of the COOH terminal and 3'UTR of XTMa2 and XTMa7 sequences. Amino acid identity is indicated by dots and stop codons by (*). Polyadenylation signals are underlined. (B) Organization of the Xenopus laevis a-TM 3' genomic region and schematic representation of the two skeletal encoding mRNAs produced. Only the mRNA portions relevant to the study are shown and they correspond to XTMa27 and XTMa74 probes. The size of the protected fragments obtained in RNase protection assay are indicated below the probes. Exons are shown by open boxes and introns by solid lines. The XTMa7 3'UTR region is indicated by a thick solid line. The polyA signal (A) and stop codons (*) are shown. (C) RNase protection analysis of XTMa2 and XTMa7 transcripts. Total RNA from adult striated muscles, stage 42 embryo (E) or tRNA (2) was analysed by RNase protection with XTMa27 or XTMa74 probes. M, size markers (HpaII-digested pBluescript); muscle RNAs were from longissimus dorsi (Ld), gastrocnemius (Gc) or heart (H). Synthetic sense RNA derived from XTMa2 (a2) and XTMa7 (a7) cDNAs were used as control. The discrepancy between the size of the probes (P) and the 339 nt protected fragment for XTMa27 or the 290 nt fragment for XTMa74 probe corresponds to the polylinker sequence included in the antisense probes.
Fig. 2. Developmental and spatial pattern of expression of XTMa2 and XTMa7 transcripts in embryo analysed by RNAse protection and wholemount in situ hybridization. (A) RNase protection analysis. Total RNA from different developmental stages embryos (9-42) or tRNA (2) was analysed by RNase protection with the XTMa27 probe that reveal simultaneously XTMa2 (339 nt protected fragment) and XTMa7 (214 nt protected fragments). (B) Whole-mount in situ hybridization was performed with XTMa2 and XTMa7 3'UTR specific probe and different developmental stages embryos as indicated.
