The lac operator-repressor system is functional in the mouse

We report the successful transfer of a fully functional lac operator-repressor gene regulatory system to the mouse. The key component is a lac repressor transgene that resembles a typical mammalian gene both in codon usage and structure and expresses functional levels of repressor protein in the animal. We used the repressor to regulate the expression of a mammalian reporter gene consisting of the tyrosinase promoter embedded with three short lac operator sequences and the tyrosinase coding sequence. Pigmentation of the mouse was controlled by the interaction of the lac repressor with the regulatable Tyrosinase transgene in a manner that was fully reversible by the lactose analog IPTG. Direct control of mammalian promoters by the lac repressor provides tight, reversible regulation, predictable levels of de-repressed expression, and the promise of reversible control of the endogenous genome.     

Multiple spatially specific enhancers are required to reconstruct the pattern of Hox-2.6 gene expression.

Murine Hox genes are organized into four clusters that share many features with the homeotic clusters of Drosophila. This evolutionary conservation and the clear relationships between the position of a gene within a cluster and its expression pattern have led to the suggestion that the structure of the cluster is essential for proper regulation. Using a Hox-2.6-lacZ reporter gene in transgenic mice we have shown that the overall expression pattern of the endogenous Hox-2.6 gene can be reconstructed when it is isolated from the complex. The transgene was expressed in the proper tissues, with the correct spatial distribution and temporal pattern. Furthermore, direct comparison by in situ hybridization revealed that the levels of transgene expression are similar to those of the endogenous gene. This has allowed us to define three elements that regulate particular aspects of the Hox-2.6 pattern, two of which act as spatially specific enhancers. One enhancer, region A, directed expression only in the neural tube, whereas the other, region C, specified the majority of the Hox-2.6 pattern. Both were also capable of imposing the correct boundaries of expression on heterologous promoters. The definition of such elements will allow the characterization of the trans-acting factors that mediate spatial regulation in the mammalian embryo.     

Expression of heterologous promoters in Lutzomyia longipalpis and Phlebotomus papatasi (Diptera: Psychodidae) cell lines

To establish a transient expression system for genes introduced into sand fly cell lines, we tested the expression of the luciferase reporter gene under control of different promoters. Towards this end, we lipofected cell lines obtained from New and Old World sand flies, LL-5 from Lutzomyia longipalpis Lutz & Neiva and PP-9 from Phlebotomus papatasi Scopoli, respectively. The relative levels of luciferase expression were studied under control of Drosophila melanogaster Meigen heat shock protein 70 (hsp70), human cytomegalovirus, simian virus 40 or Junonia coenia (Hübner) densovirus (P9) promoters. The Drosophila heat shock protein 70 promoter, originating from insect genes, functioned as a strong promoter in both cell lines. Promoters from the different virus genes also were capable of driving transgene expression in both cell lines.     

Redox regulation of mammalian heat shock factor 1 is essential for Hsp gene activation and protection from stress

The activation of eukaryotic heat shock protein (Hsp) gene expression occurs in response to a wide variety of cellular stresses including heat shock, hydrogen peroxide, uncoupled oxidative phosphorylation, infection, and inflammation. Biochemical and genetic studies have clearly demonstrated critical roles for mammalian heat shock factor 1 (HSF1) in stress-inducible Hsp gene expression, resistance to stress-induced programmed cell death, extra-embryonic development, and other biological functions. Activation of mammalian Hsp gene expression involves the stress-inducible conversion of HSF1 from the inactive monomer to the DNA-binding competent homotrimer. Although Hsp activation is a central conserved process in biology, the precise mechanisms for stress sensing and signaling to activate HSF1, and the mechanisms by which many distinct stresses activate HSF1, are poorly understood. In this report we demonstrate that recombinant mammalian HSF1 directly senses both heat and hydrogen peroxide to assemble into a homotrimer in a reversible and redox-regulated manner. The sensing of both stresses requires two cysteine residues within the HSF1 DNA-binding domain that are engaged in redox-sensitive disulfide bonds. HSF1 derivatives in which either or both cysteines were mutated are defective in stress-inducible trimerization and DNA binding, stress-inducible nuclear translocation and Hsp gene trans-activation, and in the protection of mouse cells from stress-induced apoptosis. This redox-dependent activation of HSF1 by heat and hydrogen peroxide establishes a common mechanism in the stress activation of Hsp gene expression by mammalian HSF1.     

Focal gene misexpression in zebrafish embryos induced by local heat shock using a modified soldering iron.

Misexpression of genes in a temporally and spatially controlled fashion is an important tool for assessing gene function during development. Because few tissue-specific promoters have been identified in zebrafish, inducible systems such as the Cre/LoxP and Tet repressor systems are of limited utility. Here we describe a new method of misexpression: local heat shock using a modified soldering iron. Zebrafish carrying transgenes under the control of a heat shock promoter (hsp70) are focally heated with the soldering iron to induce gene expression in a small area of the embryo. We have validated this method in three stable transgenic lines and at three developmental timepoints. Local heat shock is a fast, easy, and inexpensive method for gene misexpression.     

Induction of the heat shock response of E. coli through stabilization of sigma 32 by the phage lambda cIII protein

The cIII protein of phage lambda favors the lysogenic response to infection by inhibiting the degradation of the lambda cII protein, which exerts the primary control on the developmental decision for lysis or lysogeny. To study the mechanism and scope of cIII-mediated regulation, we have used plasmid systems to examine the specific effect of cIII overproduction on the growth of Escherichia coli and the synthesis of bacterial proteins. We have found that maximal production of cIII prolongs the heat-induced synthesis of E. coli heat shock proteins and provokes elevated production of heat shock proteins even at low temperature. The overproduction of heat shock proteins is correlated with a rapid inhibition of cell growth, as judged by measurements of optical density. We suggest that an overactive heat shock response inhibits bacterial growth, either because excessive production of one or more of the proteins is highly deleterious or because only heat shock promoters are transcribed efficiently. To examine the effect of cIII on sigma 32, the specificity factor for the heat shock response, we have studied the stability of sigma 32 in cells carrying both cIII- and sigma 32-producing plasmids; the half-life of sigma 32 is increased fourfold in the presence of cIII. We conclude that overproduction of cIII provokes the heat shock response by increasing the steady-state level of active sigma 32. These studies also support the concept that the rate of expression of heat shock proteins is directly correlated with the amount of active sigma 32 and that regulation of the stability of sigma 32 may be an important factor for control of the heat shock response.     

Cloning and characterization of the hsp 18.55 gene, a new member of the small heat shock gene family isolated from wine Lactobacillus plantarum

Using a molecular approach based on PCR, RT-PCR and northern blot analysis, a new member of the small heat shock family of wine, Lactobacillus plantarum, was cloned and characterized. The protein sequence deduced from the isolated gene had a calculated molecular mass of 18.548 kDa and was therefore named HSP 18.55. The gene codes for a protein homologous to the previously characterized HSP 19.3 and HSP 18.5 and is co-transcribed with an upstream gene of unknown function. Analysis of the 5' flanking region of the hsp 18.55 gene revealed the presence of putative cis elements able to bind alternative sigma factor sigma(B). Based on its structure, the gene was classified as belonging to class II of the heat shock genes according to Bacillus subtilis nomenclature for shock-responsive genes. Expression of the newly identified small heat shock gene, analyzed by RT-PCR and northern blot analysis, was induced by a wide range of abiotic stresses including heat, cold and ethanol, suggesting that the small family of heat shock genes is probably involved in the general stress response in wine L. plantarum. Moreover, the expression of hsp 18.5, hsp 18.55 and hsp 19.3 genes, analyzed over a complete culture cycle, revealed that early growing cells contained substantial amounts of hsp 18.5, hsp 18.55 and hsp 19.3 mRNAs, which rapidly declined upon entry into stationary phase.     

Immune responses to gene product of inducible promoters

Efficient gene transfer has been achieved in several animal models using different vector systems, leading to stable transgene expression. The tight control of this expression is now an important outcome for the field of gene therapy. Such regulation is likely to be required for therapeutic applications and in some instances for safety reasons. For this purpose, several regulatable systems depending on small molecules have been developed. Among these, the tetracycline and the rapamycin dependent systems have been largely used. However, if long-term regulation of the transgene has been obtained in small animal models using these inducible systems, when translational studies were initiated in larger animals, the development of an immune response against proteins involved in transgene regulation were often observed. Such immune response was especially documented when using the TetOn tetracycline regulatable system in nonhuman primates (NHP). Humoral and destructive cellular immune responses against the transactivator involved in this regulation system were documented in a large majority of NHP leading to the complete loss of the transgene regulation and expression. This review will describe the immune responses observed in these different model systems applied for transgene regulation. Focus will be finally given on future directions in which such immune responses might be surmounted, enabling long-term transgene regulation in future clinical developments of gene transfer.     

Conditional gene expression in human embryonic stem cells

Human embryonic stem cells (hESCs) possess unique properties for studying mechanisms controlling cell fate commitment during early mammalian development. Gain of function is a common strategy to study the function of specific genes involved in these mechanisms. However, transgene toxicity can be a major limitation, especially with factors influencing proliferation or differentiation. Here, we describe an efficient method based on the inducible recombinase Cre-ERT2 for conditional gene expression in hESCs and their differentiated derivatives. Using this approach, we have established several hESC sublines inducible for the expression of the enhanced green fluorescent protein and the transforming growth factor beta family member Nodal. Together, these results demonstrate that Cre-ERT2 can be used to control gene expression in undifferentiated and differentiated cells, thereby providing the first conditional transgene expression system that works effectively in hESCs. Disclosure of potential conflicts of interest is found at the end of this article.     

Chromosomal assignments of human 27-kDa heat shock protein gene family

The 27-kDa human heat shock protein (hsp27) is dually regulated by both estrogen and heat shock treatment. Its function is obscure, but the high degree of homology to the lens -crystallins and to the small heat shock proteins of Drosophilasuggests that it may serve a structural function. There are at least three related human hsp27 sequences. To provide possible insight into the dual regulation of hsp27, we have determined the chromosomal location of all these and found them to be on separate chromosomes: 3, 9, and X.