Genes that are differentially expressed in rat vibrissa follicle germinative epithelium in vivo show altered expression patterns after extended organ culture

Hair growth depends on maintenance of signalling between the dermal papilla and the germinative epithelium (GE), from which the differentiated layers of the hair fibre originate. Because no molecular studies have been reported which concentrate specifically on GE cells either in vivo or in vitro, we prepared a cDNA library enriched for messages which were highly expressed in GE cells to identify genes that may be involved in hair growth control. Of 35 subtracted library clones sequenced, 23 shared extensive homology with previously determined cDNA sequences, including LEF-1 and id4. Hair follicle organ culture models are often used to investigate the molecular basis of hair growth, although hair growth arrest occurs relatively rapidly in vitro. As an indicator of their role in follicle activities, we compared the expression of GE-specific clones in different regions of freshly isolated vibrissa follicles, with the corresponding regions of growth arrested, cultured follicles. Changes in the expression of some of these clones indicates that they could be related to fundamental cellular activities in the follicle. A library enriched for GE-specific clones therefore provides a useful source of candidate molecules for studies of follicular epithelial cell behaviour, both in vivo and in vitro.

SmtB is a metal-dependent repressor of the cyanobacterial metallothionein gene smtA: identification of a Zn inhibited DNA-protein complex

The smt locus of Synechococcus PCC 7942 contains a metal-regulated gene (smtA), which encodes a class II metallothionein, and a divergently transcribed gene, smtB, which encodes a repressor of smtA transcription. Regions containing cis-acting elements required for efficient induction, and required for smtB-dependent repression, of the smtA operator-promoter were identified. Specific interactions between proteins extracted from Synechococcus PCC 7942 and defined regions surrounding the smtA operator-promoter were detected by electrophoretic mobility shift assays. Three metallothionein operator-promoter associated complexes were identified, one of which (MAC1) showed Zn-dependent dissociation and involved a region of DNA immediately upstream of smtA. Treatment with Zn-chelators facilitated re-association of MAC1 in vitro. MAC1 was not observed in extracts from smt deficient mutants but was restored in extracts from mutants complemented with a plasmid borne smtB. SmtB is thus required for the formation of a Zn-responsive complex with the smt operator-promoter and based upon the predicted structure of SmtB we propose direct SmtB-DNA interaction exerting metal-ion inducible negative control.

Isolation of a prokaryotic metallothionein locus and analysis of transcriptional control by trace metal ions

In eukaryotes, metallothioneins (MTs) are involved in cellular responses to elevated concentrations of certain metal ions. We report the isolation and analysis of a prokaryotic MT locus from Synechococcus PCC 7942. The MT locus (smt) includes smtA, which encodes a class II MT, and a divergently transcribed gene, smtB. The sites of transcription initiation of both genes have been mapped and features within the smt operator-promoter region identified. Elevated concentrations of the ionic species of Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn elicited an increase in the abundance of smtA transcripts. There was no detectable effect of elevated metal (Cd) on smtA transcript stability. Sequences upstream of smtA, fused to a promoterless lacZ gene, conferred metal-dependent beta-galactosidase activity in Synechococcus PCC 7942 (strain R2-PIM8). At maximum permissive concentrations, Zn was the most potent elicitor in vivo, followed by Cu and Cd with slight induction by Co and Ni. The deduced SmtB polypeptide has similarity to the ArsR and CadC proteins involved in resistance to arsenate/arsenite/antimonite and to Cd, contains a predicted helix-turn-helix DNA-binding motif and is shown to be a repressor of transcription from the smtA operator-promoter.

Amplification and rearrangement of a prokaryotic metallothionein locus smt in Synechococcus PCC 6301 selected for tolerance to cadmium

Metal-tolerant cyanobacteria have been isolated from metal-polluted aquatic environments and also selected in culture, but no genes which confer metal tolerance have been described. To investigate the possibility that amplification of a prokaryotic metallothionein gene (smtA), or rearrangement of the smt locus, could be involved in the development of Cd tolerance in Synechococcus PCC 6301, Cd-tolerant lines were selected by stepwise adaptation of a Synechococcus culture. An increase in smtA gene copy number and the appearance of unique additional smtA restriction fragments (both larger and smaller) were detected in these tolerant lines (tolerant to 0.8 microM Cd, 1.3 microM Cd and 1.7 microM Cd). Stepwise adaptation was repeated by using a culture of Synechococcus PCC 6301 inoculated from a single plated colony to obtain four new lines (tolerant to 1.4 microM Cd, 1.8 microM Cd, 2.6 microM Cd and 3.2 microM Cd). Amplification of the smtA gene and development of unique smtA restriction fragments (larger and smaller) were once again detected in these tolerant lines. Amplification and rearrangement of the smt locus were only detected in the seven Cd-tolerant lines, with no evidence of amplification or rearrangement in the non-tolerant lines from which they were derived. As a control, another gene, psaE, was also monitored in these cell lines. There was no evidence of amplification or rearrangement of psaE in the non-tolerant or any of the Cd-tolerant lines.

Cyanobacterial metallothionein gene expressed in Escherichia coli. Metal-binding properties of the expressed protein

The recently isolated Synechococcus gene smtA encodes the only characterised prokaryotic protein designated to be a metallothionein (MT). To examine the metal-binding properties of its product the smtA gene was expressed in Escherichia coli as a carboxyterminal extension of glutathione-S-transferase. The pH of half dissociation of Zn, Cd and Cu ions from the expressed protein was determined to be 4.10, 3.50, 2.35, respectively, indicating a high affinity for these ions (in particular for Zn in comparison to mammalian MT). E. coli expressing this gene showed enhanced (ca. 3-fold) accumulation of Zn.