title: An extracellular matrix response element in the promoter of the LpS1 genes of the sea urchin Lytechinus pictus.
abstract: The extracellular matrix (ECM) has been shown to play an important role in development and tissue-specific gene expression, yet the mechanism by which genes receive signals from the ECM is poorly understood. The aboral ectoderm-specific LpS1-alpha and -beta genes of Lytechinus pictus , members of the Spec gene family, provide an excellent model system to study ECM- mediated gene regulation. Disruption of the ECM by preventing collagen deposition using the lathrytic agent beta-aminopropionitrile (BAPN) inhibits LpS1 gene transcription. LpS1 transcription resumes after removal of BAPN and subsequent collagen reformation. Using a chloramphenicol acetyltransferase (CAT) reporter gene assay, we show that a 125 bp region of the LpS1-beta promoter from -108 to +17 contains an ECM response element (ECM RE). Insertion of the 125 bp region into the promoter of the metallothionein gene of L. pictus, a gene unaffected by ECM disruption, caused the fused promoter to become ECM dependent. As with the endogenous LpS1 genes, CAT activity directed by the fused LpS1-beta promoter resumed in embryos recovered from ECM disruption. A mutation in a cis -acting element called the proximal G-string, which lies in the 125 bp region, caused CAT activity levels in ECM-disrupted embryos to equal that of the wild-type LpS1-bet apromoter in ECM-intact embryos. These results suggest that the intact ECM normally transmits signals to inhibit repressor activity at the proximal G-string in aboral ectoderm cells. Consistent with these results were our findings which showed that in addition to expression in the aboral ectoderm, the proximal G-string mutation caused expression of the CAT gene in oral ectoderm cells. These studies suggested that the proximal G-string serves as a binding site for negative regulation of the LpS1 genes in oral ectoderm during development. We also examined trans -acting factors binding the proximal G-string following ECM disruption. Band shift gels revealed a predominant set of slower migrating nuclear proteins from ECM-disrupted embryos which bound the proximal G-string. This work suggested that ECM disruption initiates signaling that induces a repressor to bind the ECM RE and/or modifies ECM RE binding proteins, which in turn represses LpS1 gene activity.
authors.affiliation: Department of Biology, University of Houston, Houston, TX 77204-5513, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Seid
authors.forename: R K
authors.initials: RK
authors.lastname: Ramachandran
authors.forename: J M
authors.initials: JM
authors.lastname: George
authors.forename: V
authors.initials: V
authors.lastname: Govindarajan
authors.forename: M F
authors.initials: MF
authors.lastname: González-Rimbau
authors.forename: C N
authors.initials: CN
authors.lastname: Flytzanis
authors.forename: C R
authors.initials: CR
authors.lastname: Tomlinson
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics*; D004247:DNA / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism*; D005786:Gene Expression Regulation; D011401:Promoter Regions, Genetic; D012617:Sea Urchins / Q000196:embryology / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D002135:Calcium-Binding Proteins; C099544:LpS1 protein, Lytechinus pictus; D014157:Transcription Factors; D004247:DNA