Alpha 1(IV) and alpha 2(IV) collagen genes are regulated by a bidirectional promoter and a shared enhancer.

Abstract

Collagen IV is the major structural component of basement membranes and is a heterotrimer composed of two al(IV) and one a2(IV) chains. Most collagen genes are dispersed in the human genome, such as the genes for collagen I, which are located on chromosomes 7 [al(I)] and 17 [a2(I)].In contrast, we have found that the murine al(IV) and a2(IV) collagen chain genes exist in a head-to-head arrangement on opposite strands separated by 130 base pairs. By transfecting various portions of these genes into cells, we have found that transcription of the al(IV) and t2(IV) genes is regulated by a bidirectional promoter located between the two genes working in concert with an enhancer located in the frst intron of the al(IV) chain gene.The collagen family is composed of >20 distinct gene products coding for a variety ofhomotrimeric and heterotrimeric proteins (1). Most of the collagen genes are dispersed throughout the genome with the exception of the collagen IV and collagen VI genes (2). In the case of collagen IV, composed of two al(IV) and a2(IV) chains, the human genes have been mapped to the same segment of chromosomes 13q (3, 4). More recently, the al(IV) and a2(IV) genes were determined to be separated by <650 kilobases (kb) by pulse-field electrophoresis (5).Collagen IV, found exclusively in basement membranes, is synthesized by a variety of cultured cells, including epithelial, endothelial, muscle, and certain tumor cells (6). F9 teratocarcinoma cells provide a unique system for studying the coordinate gene regulation of the al(IV) and a2(IV) chain genes.Undifferentiated F9 teratocarcinoma cells produce very low amounts of mRNA for the al(IV) and a2(IV) chains but are rapidly induced to synthesize these mRNAs in large amounts by treatment with retinoic acid and dibutyryl cAMP (7). We have begun to identify cis-acting elements necessary for celland tissue-specific expression of the al(IV) chain gene and found that the promoter for this gene requires an enhancer located in the first intron for effective transcription (8). This sequence in the first intron was defined as an enhancer based on its ability to stimulate transcription, independent of orientation and distance. Here we report that the a2(IV) collagen gene is located 130 base pairs (bp) away in a head-to-head orientation with the al(IV) chain gene. We also show that the al(IV) and a2(IV) chain genes share a bidirectional promoter that utilizes the same enhancer within the first intron of the al(IV) collagen gene for efficient transcriptional activity. This unique gene organization and sharing of regulatory elements may be important in the coordinate expression of these genes during differentiation and development.EXPERIMENTAL PROCEDURES constructed from the promoterless pSVOCAT-X plasmid (8).The structure of the 0.78-kb promoter-CAT construct for the al(IV) (p47A) containing nucleotides 939-163 has been described (8). p47B contains nucleotides 163-939 in the opposite orientation of p47A. The DNA fragment in p47B includes 5' flanking DNA, first exon an...

Collagen IV is essential for basement membrane stability but dispensable for initiation of its assembly during early development

“…Targeted inactivation of the Col4a1/Col4a2 genes does not interfere with early embryonic development The Col4a1 and Col4a2 genes are closely linked on mouse chromosome 8 in a unique head-to-head arrangement and separated by a short, shared promoter region similar to the human genes (Burbelo et al, 1988;Pöschl et al, 1988). The first exon of Col4a1 and exons 1-3 of Col4a2 encode the 5′ untranslated regions together with the signal peptides, respectively.…”

A GC box in the bidirectional promoter is essential for expression of the human dihydrofolate reductase and mismatch repair protein 1 genes

“…Promoters of several mammalian genes have been shown to have bidirectional activity [14,15,18,19]. However, none of these promoters has been characterized in detail.…”

Systematic Analysis of Head-to-head Gene Organization: Evolutionary Conservation and Potential Biological Relevance

“…This gene organization was first observed in the investigation of mouse DHFR gene [3]. Subsequently, SURF-1/SURF-2 [4], COL4A1/COL4A2 [1], RanBP1/Htf9-c [5], E14/ATM [6], BRCA1/NBR2 [7], DNA-PKcs/MCM4 [8], FEN1/C11orf10 [9], and so on were identified in human, hamster, rat, or mouse through individual experiments. Of them, many cases, such as DHFR/REP3 [10], SURF-1/SURF-2 [11], E14/ATM [6], and TK/ KF [12], were found to be conserved among mammalian species.…”