Modeling bidirectional transcription using silkmoth chorion gene promoters

Bidirectional transcription is an interesting feature of eukaryotic genomes; yet not all aspects of its mechanism are understood. Silkmoth choriogenesis is a model system for studying transcriptional regulation at the initiation level. As chorion genes comprise a large group of divergently transcribed gene pairs, we are presented with the possibility of investigating the intricacies of bidirectional transcription. Their well characterized 5′ regulatory regions and expression profiles lay the foundation for investigating protein:protein and protein:DNA interactions, and RNA polymerase function during oocyte development. In this article we summarize current knowledge on chorion gene regulation and propose an approach to modeling bidirectional transcription using chorion promoters. © 2009 Landes Bioscience

The possible evolutionary significance of repeat elements near and within an early chorion gene in the late chorion locus of Bombyx mori

Three β-type early chorion gene copies (6F76.1, 6F76.2, and 6F76.3) are dispersed in the late region of chorion locus Chl-2. Detailed analysis of the 5′-flanking region and the intron of 6176.1 shows that they contain sequences that are homologous to Bombyx mori Bm l repeat elements. Interestingly, the Bm l -type segment of the intron is interrupted by the insertion of a sequence that shows significant similarities with part of an intron of B. mori and Bombyx mandarina fibroin genes, and with part of the 3′-flanking region of B. mori prothoracicotropic hormone and tRNA-Glu genes; this sequence may represent a new repetitive, possibly transposable, element of B. mori. Following the Bm1-homologous sequence of the 6176.1 5′-flanking region and preceding the gene promoter region, a short DNA segment shows sequence motifs that are also present in the ErA.1 promoter region. The occurrence of these sequences near one end or within the Bm1 repeat element is suggestive of complex sequence transfer events. Comparative analysis of known B. mori chorion α-gene promoters and of Bm1 repeat elements suggests, with marginal statistical significance, that these two sets of sequences contain common elements. © 1992, Springer-Verlag New York Inc. All rights reserved

A modified chromatin-immunoprecipitation protocol for silkmoth ovarian follicular cells reveals C/EBP and GATA binding modes on an early chorion gene promoter.

Standard Chromatin immunoprecipitation protocols have been designed to suit studies performed on cell line cultures or yeast cells growing in liquid cultures. In these cases cross-linking/fixation takes place directly in the growing medium of the cells by the addition of a general fixation reagent. When applied on whole isolated silkmoth follicles, this procedure results in poor release of follicular cells from the basal membrane and lower yield of cross-linked chromatin. We present a modification to the standard protocol, where detachment of follicular cells from the basal membrane of the egg and nuclei isolation precedes formaldehyde-mediated cross-linking. We also discuss application of the modified method for the identification of distinct BmC/EBP and BmGATAbeta binding modes on a chorion gene promoter from the Er1.A/B early gene pair

Three copies of the early gene 6F6 are interspersed in and around the late chorion gene cluster of Bombyx mori

The developmentally regulated chorion genes of the silkmoth, Bombyx mori, are clustered in two genetic loci (Chl-2 and Ch3) of chromosome 2, which are separated by approximately 4 centiMorgans. Early genes are clustered in chorion locus Ch3, whereas Ch l-2 contains all of the late genes in a continuous region of 140 kb, which is sandwiched between two regions containing most of the middle chorion genes. The late-gene area has been extensively studied and was considered to contain only late genes coding for chorion proteins of exceptionally high cysteine content organized in tightly clustered α/β gene pairs. In the present paper we report the unexpected presence of three dispersed copies (6F6.1, 6F6.2, 6F6.3) of an early β-gene, which disrupts the continuity of the late locus. Hybridization data indicate that 6F6.2 corresponds to the previously characterized m6F6 cDNA clone and that 6F6.1 and 6F6.3, but not 6F6.2, are adjacent to α-type genes. Determination of the complete sequence of 6F6.1 and of the major exon of the A-gene near it shows that these two genes have a convergent rather than a divergent direction of transcription and thus do not constitute a typical gene pair. The sequence data further suggest that 6F6.1 is transcriptionally active. The three dispersed 6F6 gene copies are localized at points of inversion of the polarity of neighboring gene pairs and their locations in this locus indicate complex gene rearrangement events. © 1992, Springer-Verlag New York Inc. All rights reserved

A modified chromatin-immunoprecipitation protocol for silkmoth ovarian follicular cells reveals C/EBP and GATA binding modes on an early chorion gene promoter

Standard Chromatin immunoprecipitation protocols have been designed to suit studies performed on cell line cultures or yeast cells growing in liquid cultures. In these cases cross-linking/fixation takes place directly in the growing medium of the cells by the addition of a general fixation reagent. When applied on whole isolated silkmoth follicles, this procedure results in poor release of follicular cells from the basal membrane and lower yield of cross-linked chromatin. We present a modification to the standard protocol, where detachment of follicular cells from the basal membrane of the egg and nuclei isolation precedes formaldehyde-mediated cross-linking. We also discuss application of the modified method for the identification of distinct BmC/EBP and BmGATAβ binding modes on a chorion gene promoter from the Er1.A/B early gene pair. © 2008 Springer Science+Business Media B.V

Three copies of the early gene 6F6 are interspersed in and around the late chorion gene cluster of Bombyx mori

The developmentally regulated chorion genes of the silkmoth, Bombyx mori, are clustered in two genetic loci (Chl-2 and Ch3) of chromosome 2, which are separated by approximately 4 centiMorgans. Early genes are clustered in chorion locus Ch3, whereas Ch l-2 contains all of the late genes in a continuous region of 140 kb, which is sandwiched between two regions containing most of the middle chorion genes. The late-gene area has been extensively studied and was considered to contain only late genes coding for chorion proteins of exceptionally high cysteine content organized in tightly clustered α/β gene pairs. In the present paper we report the unexpected presence of three dispersed copies (6F6.1, 6F6.2, 6F6.3) of an early β-gene, which disrupts the continuity of the late locus. Hybridization data indicate that 6F6.2 corresponds to the previously characterized m6F6 cDNA clone and that 6F6.1 and 6F6.3, but not 6F6.2, are adjacent to α-type genes. Determination of the complete sequence of 6F6.1 and of the major exon of the A-gene near it shows that these two genes have a convergent rather than a divergent direction of transcription and thus do not constitute a typical gene pair. The sequence data further suggest that 6F6.1 is transcriptionally active. The three dispersed 6F6 gene copies are localized at points of inversion of the polarity of neighboring gene pairs and their locations in this locus indicate complex gene rearrangement events. © 1992, Springer-Verlag New York Inc. All rights reserved

Silkmoth chorion gene regulation revisited: promoter architecture as a key player.

Regulation of silkmoth chorion genes has long been used as a model system for studying differential gene expression. The large numbers of genes, their overlapping expression patterns and the overall complexity of the system hinted towards an elaborate mechanism for transcriptional control. Recent studies, however, offer evidence of a molecular pathway governed by the interplay between two general transcription factors, CCAAT enhancer binding proteins (C/EBP) and GATA, an architectural protein, high mobility group A and a chromatin remodeller, chromo-helicase/ATPase-DNA binding protein 1. In this review we present a parsimonious model that adequately describes regulation of transcription across all temporally regulated chorion genes, and propose a role for promoter architecture

BmCbZ, an insect-specific factor featuring a composite DNA-binding domain, interacts with BmC/EBPgamma.

A novel factor featuring a composite AT hook/basic region-leucine zipper DNA-binding domain was isolated from Bombyx mori follicular cells. Screening of EST databases derived from a variety of metazoans revealed the exclusive presence of BmCbZ homologues in insect species. BmCbZ characteristic features and gene organization are discussed, in comparison to other known bZIP factors. We concordantly propose that this factor establishes a new insect-specific bZIP family. We further present the isolation of the silkmoth homologue of mammalian C/EBPgamma, BmC/EBPgamma, and in vitro evidence for its interaction with BmCbZ. The formation of a BmCbZ-BmC/EBPgamma heterodimer is a prerequisite for binding to specific C/EBP recognition sites on chorion gene promoters, most probably via both major and minor groove interactions

BmCbZ, an insect-specific factor featuring a composite DNA-binding domain, interacts with BmC/EBPγ

A novel factor featuring a composite AT hook/basic region-leucine zipper DNA-binding domain was isolated from Bombyx mori follicular cells. Screening of EST databases derived from a variety of metazoans revealed the exclusive presence of BmCbZ homologues in insect species. BmCbZ characteristic features and gene organization are discussed, in comparison to other known bZIP factors. We concordantly propose that this factor establishes a new insect-specific bZIP family. We further present the isolation of the silkmoth homologue of mammalian C/EBPγ, BmC/EBPγ, and in vitro evidence for its interaction with BmCbZ. The formation of a BmCbZ-BmC/EBPγ heterodimer is a prerequisite for binding to specific C/EBP recognition sites on chorion gene promoters, most probably via both major and minor groove interactions. © 2005 Elsevier Inc. All rights reserved