Regulated spatial expression of fusion gene constructs with the 5′ upstream region of Halocynthia roretzi muscle actin gene in Ciona savignyi embryos

pHrMA4a-Z is a recombinant plasmid in which about 1.4 kb of the 5 flanking region of a gene for muscle actin HrMA4a from the ascidian Halocynthia roretzi is fused with the coding sequence of a bacterial gene for -galactosidase (lac-Z). In this study, we examined the expression of the fusion gene construct when it was introduced into eggs of another ascidian, namely Ciona savignyi. When a moderate amount of linearized pHrMA4a-Z was introduced into fertilized Ciona eggs, the expression of the reporter gene was evident in muscle cells of the larvae, suggesting that both species share a common machinery for the expression of muscle actin genes. The 5 upstream region of HrMA4a contains several consensus sequences, including a TATA box at -30, a CArG box at -116 and four E-boxes within a region of 200 bp. A deletion construct, in which only the 216-bp 5 flanking region of HrMA4a was fused with lac-Z, was expressed primarily in larval muscle cells. However, another deletion construct consisting of only the 61-bp upstream region of HrMA4a fused with lac-Z was not expressed at all. When pHrMA4a-Z or pHrMA4a-Z (–216) was injected into each of the muscle-precursor blastomeres of the 8-cell embryo, expression of the reporter gene was observed in larval muscle cells in a lineage-specific fashion. However, expression of the reporter gene was not observed when the plasmid was injected into non-muscle lineage. Therefore, the expression of the reporter gene may depend on some difference in cytoplasmic constituents between blastomeres of muscle and non-muscle lineage in the 8-cell embyo.     

Quantity of prelocalized maternal factor is associated with the timing of initiation of an epidermis-specific gene expression of the ascidian embryo

 We produced half-egg-volume ascidian embryos by dividing the unfertilized egg of Halocynthia roretzi at the equatorial plane, and investigated the timing of the initiation of the expression of three tissue-specific genes, a muscle-specific actin gene HrMA4, a notochord-specific gene As-T and an epidermis-specific gene HrEpiC in the half-egg-volume embryos of the animal side and those of the vegetal side. The timing of the onset of HrMA4 and As-T expression in both the animal- and vegetal-half embryos and that of HrEpiC expression in the animal-half embryos were essentially the same as that of normal embryos. In contrast, the timing of HrEpiC expression in the vegetal-half embryos was delayed by one division cycle compared with the normal embryos. This delay was partially recovered by increasing the amount of unfertilized egg cytoplasm of the animal hemisphere, suggesting that the timing of HrEpiC expression is regulated by the amount of a maternal factor which is distributed abundantly in the animal hemisphere of the unfertilized egg. Received: 27 August 1997 / Accepted: 1 February 1998     

Introduction and Expression of Recombinant Genes in Ascidian Embryos

In order to examine the expression of exogenous genes introduced into ascidian eggs, two recombinant plasmids pmiwZ and pHrMA4aCAT were microinjected into the cytoplasm of fertilized eggs of Ciona savignyi and Halocynthia roretzi , respectively. The plasmid pmiwZ contains the coding sequence of bacterial β-galactosidase gene ( lac-Z ) fused with animal gene promoters, while pHrMA4aCAT was constructed by fusing about 1.4-kb long 5' flanking region of H. roretzi muscle actin gene HrMA4a with bacterial chloramphenicol acetyltransferase gene ( CAT ). Injection of approximately 160 pl of 10 μg/ml pmiwZ DNA into Ciona eggs did not affect the embryogenesis, although introduction of the same volume of 30 μg/ml pmiwZ DNA resulted in abnormal development of injected eggs. When the expression of lac-Z was examined by histochemical detection of the enzyme activity, the expression was evident in the early tailbud embryos and later stage embryos, and larvae, irrespective of linear or circular form of the plasmid. The enzyme activity appeared in various cell-types including epidermis, nervous system, endoderm, mesenchyme, notochord, and muscle. In contrast, when pHrMA4aCAT was introduced into Halocynthia eggs and the appearance of CAT protein was examined later by the anti-CAT antibody, the CAT expression was restricted to muscle cells. These results indicate that the recombinant genes introduced into ascidian eggs could express during embryogenesis and that the 1.4-kb long 5' flanking region of HrMA4a contains regulatory sequences enough for the appropriate spatial and temporal expression of the gene.     

Both muscle-specific and ubiquitous nuclear factors are required for muscle-specific expression of the myosin heavy-chain beta gene in cultured cells.

Expression of the myosin heavy-chain beta gene is controlled by multiple cis-acting regulatory elements in the 5' flanking region; two of these, referred to as A (-276 to -263) and B (-207 to -180), are essential for conferring muscle-specific activation on homologous and heterologous promoters. Here we report on the identification of nuclear protein factors that specifically bind to these two elements. By using the A element as a probe, as well as nuclear extracts from muscle cells, we found two protein-DNA complexes that displayed distinct bands in a gel mobility shift assay but had identical methylation interference patterns. One complex was present mainly in nuclear extracts from undifferentiated muscle and nonmuscle cells, whereas the other was observed mainly in nuclear extracts from differentiated muscle cells. Thus, the muscle-specific complex formation with the A element appears to be involved in determining tissue-specific expression. Furthermore, competition analysis demonstrated that the A-element-binding factors also bind to the muscle-CAT motif in the cardiac troponin T gene. By using the B element as a probe, we saw similar patterns of gel-shifted bands and methylation interference in nonmuscle and muscle nuclear extracts. In addition, both elements A and B were found to be necessary for tissue-specific expression, suggesting that the muscle-specific activation of the myosin heavy-chain beta gene may require interaction between a muscle-specific and a ubiquitous protein-DNA complex.     

Molecular characterization of differentially expressed TXNIP gene and its association with porcine carcass traits

Thioredoxin interacting protein (TXNIP), which plays a regulatory role in lipid metabolism and immune regulation, is down-regulated expressed in F₁ hybrids Landrace?×?Yorkshire skeletal muscle. Here we described the molecular characterization of porcine TXNIP gene. The full-length cDNA contains a coding sequence of 1,176?bp nucleotides with untranslated regions of 263?bp at 5′-end and 441?bp at 3′-end, respectively. The predicted molecular mass and isoelectric point of porcine TXNIP is 43.81?kDa and 7.385, respectively. The deduced 391 amino acids exhibit high identity with other mammalian TXNIP. The TXNIP gene contains eight coding exons and seven non coding introns, spans approximately 3,348?bp. The expression of porcine TXNIP mRNA is almost absent in Landrace?×?Yorkshire and lower level in 6-month-old pigs during skeletal muscle development. Other stages and breeds were high level expressed. Statistical analysis showed the TXNIP gene polymorphism (c.575-4T>C) was different between F₁ hybrids and their parents, was highly associated with dressing percentage (DP) and thorax–waist fat thickness (TFT) in the Yorkshire?×?Meishan F₂ population. The possible role of TXNIP was discussed.     

Sequence analysis of the 5′-untranslated region of the human H1 histamine receptor-encoding gene

A clone containing the H₁ histamine receptor (H₁HR)-encoding gene was isolated from a human genomic DNA library. The 5′-UTR of the H₁HR gene reported here differs upstream from bp −142 from that reported previously [Fukui et al., Biochem. Biophys. Res. Comm. 201 (1994) 894–901]. PCR amplification utilizing primer pairs derived from the 5′-UTR reported herein amplified a DNA fragment of the expected size from human genomic DNA whereas 5′-UTR primers derived from the Fukui et al. sequence did not yield a PCR product. The 5′-UTR of H₁HR contains potential TATA and CCAAT boxes, a CACCC sequence, potential GREs and other DNA-binding motifs.     

Tissue specificity of 3′-untranslated sequence of myosin light chain gene: Unexpected interspecies homology with repetitive DNA

Using the 3′ noncoding and coding sequences of chick heart myosin light chain mRNA cloned into Escherichia coli as probes, it was observed that, while the coding sequence shared homology with myosin light-chain mRNAs from other sources, the 3′ noncoding sequence was specific for chick heart muscle. This property was used to detect chick heart-specific myosin light-chain gene activity in chick blastoderms of very early developmental stages where cells of different muscle origins cannot be distinguished morphologically. However, in spite of the tissue-specific divergence of the 3′ noncoding sequence of myosin light-chain gene, which is present in a single copy in the chick genome, a surprising homology with DNA from such a diverse source like Dictyostelium discoideum was noted. The sequence homologous to chick myosin light-chain DNA was apparently present in a high repetition frequency in the Dictyostelium genome.     

Determinative mechanisms in secondary muscle lineages of ascidian embryos: development of muscle-specific features in isolated muscle progenitor cells

Muscle cells of the ascidian larva originate from three different lines of progenitor cells, the B-line, A-line and b-line. Experiments with 8-cell embryos have indicated that isolated blastomeres of the B-line (primary) muscle lineage show autonomous development of a muscle-specific enzyme, whereas blastomeres of the A-line and b-line (secondary) muscle lineage rarely develop the enzyme in isolation. In order to study the mechanisms by which different lines of progenitors are determined to give rise to muscle, blastomeres were isolated from embryos of Halocynthia roretzi at the later cleavage stages when conspicuous restriction of the developmental fate of blastomeres had already occurred. Partial embryos derived from B-line muscle-lineage cells of the 64-cell embryo (B7.4, B7.5 and B7.8) showed autonomous expression of specific features of muscle cells (acetylcholinesterase, filamentous actin and muscle-specific antigen). In contrast, b-line muscle-lineage cells, even those isolated from the 110-cell embryo (b8.17 and b8.19), did not express any muscle-specific features, even though their developmental fate was mainly restricted to generation of muscle. Isolated A-line cells from the 64-cell embryos (A7.8) did not show any features of muscle differentiation, whereas some isolated A-line cells from the 110-cell embryos (A8.16) developed all three above-mentioned features of muscle cells. This transition was shown to occur during the eighth cell cycle. These results suggest that the mechanism involved in the process of determination of the secondary-lineage muscle cells differs from that of the primary-lineage muscle cells. Interaction with cells of other lineages may be required for the determination of secondary precursors to muscle cells. The presumptive b-line and A-line muscle cells that failed to express muscle-specific features in isolation did not develop into epidermal cells. Thus, although interactions between cells may be required for muscle determination in secondary lineages, the process may represent a permissive type of induction and may differ from the processes of induction of mesoderm in amphibian embryos.