An enhancer for transcription of collagen IV genes is activated by F9 cell differentiation

Isolation and heterologous transformation analysis of a pollen-specific promoter from wheat (Triticum aestivum L.)

The promoter of a pollen-specific gene TaPSG719 was isolated from wheat (Triticum aestivum L.) by inverse-PCR (IPCR). Sequence analysis revealed that the promoter contains two cis-acting elements (AGAAA and GTGA) known to confer anther/pollen-specific gene expression which suggests that the promoter of TaPSG719 gene is a pollen-specific one. To ascertain the regulatory function of TaPSG719 promoter, two deleted fragments (-1,776 to -1 bp and -1,019 to -1 bp) were fused to the beta-glucuronidase (GUS) gene and transformed into tobacco plants. Similar GUS expression patterns were observed in all transformed plants and its activity was detected exclusively in pollen. No GUS activity in any other floral or vegetative tissue was observed. The results confirm that TaPSG719 promoter is pollen-specific and active during the middle stages of pollen development till anther matured, and it can drive pollen-specific gene expression across the species.

Sox9a regulation of ff1a in zebrafish (Danio rerio) suggests an involvement of ff1a in cartilage development

The NR5A family of orphan nuclear receptors has been implicated in development of the vertebrate embryo, but their exact role remains largely unknown. To evaluate the regulation and developmental role for ff1a (NR5A2) in zebrafish (Danio rerio), we performed morpholino knockdown to block translation of the ff1a gene and the upstream located sox9a gene during embryogenesis. Using a newly developed antibody against Ff1a we could show that the ff1a morpholinos were functional and that a reduction in the expression of Ff1a correlated to altered phenotypes. The role of Sox9a in ff1a gene regulation and function was studied using sox9a morpholinos. Knock-down of sox9a resulted in abolished ff1a signals in the somites, mandibular arches and pharyngeal arches, while the pectoral fin signal remained. The reduction in Ff1a levels correlated to truncated tails and cranio-facial malformation. As Sox9a is involved in chondrocyte development we analysed for cartilage formation and found that blocking translation of either sox9a or ff1a also blocked cartilage formation. In light of the results, the present study suggests a novel function of ff1a in chondrocyte development.

SRY-related HMG box 9 regulates the expression of Col4a2 through transactivating its enhancer element in mesangial cells

Accumulation of alpha1(IV) and alpha2(IV) collagen is one of the characteristic pathological changes in glomerulosclerosis. Although the Col4a2 gene is known to have a 0.3-kb critical enhancer element with the GAACAAT motif, which transcription factor binds and transactivates this motif has not been identified. In this study, we found that SRY-related HMG box 9 (SOX9) was bound to the GAACAAT motif in the Col4a2 enhancer in vitro and in vivo in mesangial cells. SOX9 strongly activated this enhancer when cotransfected with Col4a2 enhancer-promoter construct in mesangial cells and Swiss/3T3 cells. Mutation in the GAACAAT motif eliminated the activation by SOX9. Furthermore, transforming growth factor-beta (TGF-beta) treatment induced the expression of SOX9 and Col4a2, and a small interfering RNA against SOX9 reduced Col4a2 expression induced by TGF-beta treatment in mesangial cells. In vivo, we found that the expression of SOX9 was dramatically increased along with the expression of TGF-beta and Col4a2 in mouse nephrotoxic nephritis. These results indicate that SOX9 is essential for Col4a2 expression in mesangial cells and might be involved in the accumulation of alpha2(IV) collagen in experimental nephritis.

Identification of an upstream enhancer in the mouse laminin alpha 1 gene defining its high level of expression in parietal endoderm cells

Laminin-1 is the major component of the embryonic basement membrane and consists of alpha1, beta1, and gamma1 chains. The expression of laminin-1 is induced in mouse F9 embryonal carcinoma cells upon differentiation into parietal endoderm through transcriptional up-regulation of the genes encoding these subunits. Here, we identified a 435-bp enhancer in the 5'-flanking region of the mouse laminin alpha1 (LAMA1) gene that activated its transcription in a differentiation-dependent manner. This enhancer was also active in PYS-2 parietal yolk sac-derived cells but not in NIH/3T3 fibroblasts, indicating that it was a parietal endoderm-specific enhancer. This enhancer was also active in Engelbreth-Holm-Swarm (EHS) tumor-derived cells characterized by excessive production of laminin-1 and other basement membrane components, suggesting that EHS tumors have a transcriptional control mechanism similar to that of parietal endoderm cells. Electrophoretic mobility shift analyses revealed four protein binding sites (PBS1-PBS4) in the 435-bp region. However, these DNA-binding proteins were detected not only in parietal endoderm cells (i.e. differentiated F9 cells, PYS-2 cells, and EHS tumor-derived cells) but also in undifferentiated F9 cells and NIH/3T3 cells. Mutational analyses revealed that three of these binding sites (PBS2, PBS3, and PBS4) function synergistically to confer the parietal endoderm-specific enhancer activity. The proteins binding to PBS2 and PBS4 were identified as the Sp1/Sp3 family of transcription factors and YY1, respectively.

Disassociation of MAPK activation and c-Fos expression in F9 embryonic carcinoma cells following retinoic acid-induced endoderm differentiation

Retinoic acid induces cell differentiation and suppresses cell growth in a wide spectrum of cell lines, and down-regulation of activator protein-1 activity by retinoic acid contributes to these effects. In embryonic stem cell-like F9 teratocarcinoma cells, which are widely used to study retinoic acid actions on gene regulation and early embryonic differentiation, retinoic acid treatment for 4 days resulted in suppression of cell growth and differentiation into primitive and then visceral endoderm-like cells, accompanied by a suppression of serum-induced c-Fos expression. The MAPK (ERK) pathway was involved in mitogenic signaling in F9 cells stimulated with serum. Surprisingly, although c-Fos expression was reduced, the MAPK activity was not decreased by retinoic acid treatment. We found that retinoic acid treatment inhibited the phosphorylation of Elk-1, a target of activated MAPK required for c-Fos transcription. In F9 cells, the MAPK/MEK inhibitor PD98059 suppressed Elk-1 phosphorylation and c-Fos expression, indicating that MAPK activity is required for Elk-1 phosphorylation/activation. Phosphoprotein phosphatase 2B (calcineurin), the major phosphatase for activated Elk-1, is not the target in the disassociation of MAPK activation and c-Fos expression since its inhibition by cyclosporin A or activation by ionomycin had no significant effects on serum-stimulated c-Fos expression and Elk-1 phosphorylation. Thus, we conclude that retinoic acid treatment to induce F9 cell differentiation uncouples Ras/MAPK activation from c-Fos expression by reduction of Elk-1 phosphorylation through a mechanism not involving the activation of phosphoprotein phosphatase 2B.

Two genes, COL4A3 and COL4A4 coding for the human alpha3(IV) and alpha4(IV) collagen chains are arranged head-to-head on chromosome 2q36

We first isolated and characterized genomic DNA fragments that cover the 5' flanking sequences of COL4A3 and COL4A4 encoding the human basement membrane alpha3(IV) and alpha4(IV) collagen chains, respectively. Nucleotide sequence analysis indicated that the two genes are arranged head-to-head. To determine transcription start site for COL4A4 gene, we performed RACE and RNase protection assays, indicating that there are two alternative transcripts presumably derived from two different promoters. Interestingly, one transcription start site (from exon 1') of COL4A4 is only 5 bp away from the reported transcription start site of COL4A3, whereas the other transcript (from exon 1) starts 373 nucleotides downstream from the first one, generating the two kinds of transcripts that differ in the 5' UTR regions. Expression of these two transcripts appears tissue-specific; exon 1 transcript was expressed predominantly in epithelial cells, while exon 1' transcript showed rather ubiquitous and low expression. The nucleotide sequence of the promoter region is composed of dense CpG dinucleotides, GC boxes, CTC boxes and a CCAAT box but no TATA box. These results provide information to delineate the promoter activity for the tissue-specific expression of the six type IV collagen genes and basement membrane assembly in different tissues and organs.

Structure of the rat collagen IV promoter

We have isolated a 1.6 kb clone from a rat genomic library which contains the bidirectional collagen IV promoter, flanked by exons coding for the alpha 1 (IV) and alpha 2 (IV) collagen chains. There are at least two transcription start sites within both the alpha 1 (IV) and alpha 2 (IV) collagen genes. Rat mesangial cells were transfected with chloramphenicol acetyltransferase (CAT) reporter plasmids containing segments of the promoter and 5' flanking region, in both the alpha 1 (IV) and alpha 2 (IV) orientations. Our results suggest that transcriptional efficiency of the bidirectional promoter is more efficient in the alpha 2 (IV) direction than in the alpha 1 (IV) direction.

Coordinate gene expression of the alpha3, alpha4, and alpha5 chains of collagen type IV. Evidence from a canine model of X-linked nephritis with a COL4A5 gene mutation

Canine X-linked hereditary nephritis is an animal model for human X-linked hereditary nephritis with a premature stop codon in the alpha5(IV) gene of collagen type IV. We used this model to examine the other alpha(IV) chains at the mRNA and protein level in the kidney, since in human X-linked hereditary nephritis, the alpha3(IV) and alpha4(IV) chains are often absent from the glomerular basement membrane, although both are encoded by autosomal genes. cDNA probes for the alpha1(IV)-alpha6(IV) chains were generated from normal dog kidney using the polymerase chain reaction. Sequences were >/=88% identical at the DNA level and >/=92% identical at the protein level to the respective human alpha(IV) chains. By Northern analysis, transcripts for the alpha1(IV), alpha2(IV), and alpha6(IV) chains were detected at comparable levels in both normal and affected male dog kidney RNA. As previously shown, the transcript for the alpha5(IV) chain was reduced to approximately 10% of normal. Unexpectedly, the alpha3(IV) and alpha4(IV) transcripts were both decreased >/=77% in affected male dog kidney, suggesting a mechanism coordinating the expression of these three basement membrane components. The NC1 domain of collagen type IV isolated from normal dog glomeruli was positive for the alpha3(IV), alpha4(IV), and alpha5(IV) chains by Western blotting. In contrast, in the NC1 domain isolated from affected dog glomeruli, these three chains were not detectable, except for a trace of alpha3(IV) dimer. In X-linked hereditary nephritis, the absence of the alpha3(IV) and alpha4(IV) chains from glomerular basement membrane may reflect factors acting at the transcriptional and/or translational level in addition to the protein assembly level.

Structural organization of the human and mouse laminin beta2 chain genes, and alternative splicing at the 5' end of the human transcript

We have determined the structural organization of the human and mouse genes that encode the laminin beta2 chain (s-laminin), an essential component of the basement membranes of the neuromuscular synapse and the kidney glomerulus. The human and mouse genes have a nearly identical exon-intron organization and are the smallest laminin chain genes characterized to date, due to the unusually small size of their introns. The laminin beta2 chain genes of both species consist of 33 exons that span </=12 kilobase pairs of genomic DNA. The exon-intron pattern of the laminin beta2 chain gene is also highly similar to that of the human genes encoding the homologous laminin beta1 and beta3 chains. The putative promoter regions of the human and mouse laminin beta2 chain genes have features characteristic of the promoters of genes that have a limited tissue expression. Considerable conservation of the intron sequences of the mouse and human genes was observed. The first intron of the human gene, located 1 base pair upstream of the translation start codon, contains a non-consensus 5' splice site. This intron was shown to be inefficiently spliced in humans, suggesting that post-transcriptional mechanisms may be involved in the regulation of laminin beta2 chain gene expression.

Positive elements in the laminin gamma 1 gene synergize to activate high level transcription during cellular differentiation

Transcription of the murine laminin gamma 1 gene is activated during retinoic acid/cAMP induced differentiation of F9 embryonal carcinoma cells. Positive transcription control elements associated with two DNase I hypersensitive regions in the large first intron of the gene have been identified which confer a differentiation response on the laminin gamma 1 promoter. However, the kinetics of transcriptional activation suggest each DNA region interacts with transcription factors appearing at different times during differentiation. Synergy between the two regions in cis causes high level activation.