The transcriptional programs that specify the distinct components of the cardiac conduction system are poorly understood, in part due to a paucity of definitive molecular markers. In the present study we show that a cGATA-6 gene enhancer can be used to selectively express transgenes in the atrioventricular (AV) conduction system as it becomes manifest in the developing multichambered mouse heart. Furthermore, our analysis of staged cGATA-6/lacZ embryos revealed that the activity of this heart-region-specific enhancer can be traced back essentially to the outset of the cardiogenic program. We provide evidence that this enhancer reads medial/lateral and anterior/posterior positional information before the heart tube forms and we show that the activity of this enhancer becomes restricted at the heart looping stage to AV myocardial cells that induce endocardial cushion formation. We infer that a deeply-rooted heart-region-specific transcriptional program serves to coordinate AV valve placement and AV conduction system formation. Lastly, we show that cGATA-6/Cre mice can be used to delete floxed genes in the respective subsets of specialized heart cells.

We screened a chicken liver cDNA expression library with a probe spanning the distal region of the chicken vitellogenin II (VTGH) gene promoter and isolated clones for a transcription factor that we have named VBP (for vitellogenin gene-binding protein). VBP binds to one of the most important positive elements in the VTGH promoter and appears to play a pivotal role in the estrogen-dependent regulation of this gene. The protein sequence of VBP was deduced from a nearly full length cDNA copy and was found to contain a basic/zipper (bZIP) motif. As expected for a bZIP factor, VBP binds to its target DNA site as a dimer. Moreover, VBP is a stable dimer free in solution. A data base search revealed that VBP is related to rat DBP. However, despite the fact that the basic/hinge regions of VBP and DBP differ at only three amino acid positions, the DBP binding site in the rat albumin promoter is a relatively poor binding site for VBP. Thus, the optimal binding sites for VBP and DBP may be distinct. Similarities between the VBP and DBP leucine zippers are largely confined to only four of the seven helical spokes. Nevertheless, these leucine zippers are functionally compatible and appear to define a novel subfamily. In contrast to the bZIP regions, other portions of VBP and DBP are markedly different, as are the expression profiles for these two genes. In particular, expression of the VBP gene commences early in liver ontogeny and is not subject to circadian control.Genetic and biochemical studies have established that transcription by RNA polymerase II requires the assembly of a stable preinitiation complex over the proximal promoter region of each target gene (6,32 which a nonfunctional partner suppresses the activity of a functional partner. In addition to DNA binding domains (and, in some cases, dimerization domains), transcription factors also contain one or more transactivation domains that are required to mediate positive effects on the general transcriptional machinery. Subclasses of transactivation domains have been identified, and it is likely that other novel domains will be found as more transcription factors are cloned and analyzed. Much current work is directed at understanding how these activation domains function, and the notion that additional bridging factors may be involved has been advanced from several recent studies (reviewed in reference 25).Studies in our laboratory are focused on a molecular understanding of the estrogen-dependent and liver-specific transcriptional regulation of the chicken vitellogenin II (VTGII) gene. The estrogen-dependent aspect of this regulation was shown to be due to the presence of two upstream estrogen response elements, and the ability of the VTGII promoter to be activated by these elements was found to be cell type specific (5, 7). A linker scanner mutational analysis of the VTGII promoter using transient expression assays in chicken hepatoma (LMH) cells (18) and chicken embryo fibroblast cells revealed that this promoter has multiple positive elements as well as a negat...

Chicken genomes contain '=30,000 chicken repeat 1 (CR1) elements scattered among single-copy sequences, but no information has yet been presented to account for how these elements could have dispersed.

No abstract

Greenhouse, growth chamber, and laboratory studies were conducted to determine anatomical and morphological characteristics and cultural practices limiting the distribution of cogongrass, torpedograss, and johnsongrass in the United States. Cogongrass did not produce axillary buds along most of the rhizome nor regenerate when apical six-node-long rhizome segments were buried deeper than 8 cm. Both torpedograss and johnsongrass produced axillary buds along the entire lengths of their rhizomes. Torpedograss shoot emergence decreased at burial depths between 8 and 16 cm. Shoot emergence from johnsongrass rhizomes was not affected by burial as deep as 16 cm. Rhizomes of all three species were tolerant of desiccation. Cogongrass grew better in soil at pH 4.7 than in soil at pH 6.7, whereas torpedograss and johnsongrass grew equally well in either pH. It is postulated that cogongrass spread is limited by lack of axillary bud formation on most of the rhizome and the inability of rhizomes to send up new shoots if buried deeper than 8 cm. These factors could account for the intolerance of cogongrass to cultivation. Torpedograss appears to spread only vegetatively due to the lack of viable seed production.