A Drosophila model of HIV-Tat-related pathogenicity.

To analyze the mechanism of Tat-mediated HIV pathogenicity, we produced a Drosophila melanogaster strain transgenic for HIV-tat gene and induced the expression of the protein during Drosophila development. By in vitro and in vivo experiments, we demonstrated that Tat specifically binds to tubulin via the MAP-binding domain of tubulin, and that this interaction delays the polymerization of tubulin and induces a premature stop to microtubule-dependent cytoplasmic streaming. The delay in the polymerization of microtubules, the tracks for the transport of the axes determinants, alters the positioning of the dorso-ventral axis as shown by the mislocalization of Gurken and Kinesin in oocyte of Drosophila after Tat induction. These results validate the use of Drosophila as a tool to study the molecular mechanism of viral gene products and suggest that Tat-tubulin interaction is responsible for neurodegenerative diseases associated with AIDS.

A competitive PCR-based method to measure human fibroblast growth factor receptor 1-4 (FGFR1-4) gene expression.

The four members of the fibroblast growth factor receptor (FGFR) family are cell-surface membrane-spanning tyrosine kinase receptors involved in a wide spectrum of biologic processes. Much evidence also indicates that mutations in FGFR genes result in several craniosynostotic disorders and chondrodysplasias, and that changes in qualitative and quantitative FGFR expression profiles are implicated in tumor induction or progression. Here, we describe a precise and reliable competitive PCR-based assay to evaluate human FGFR1-4 gene expression. A single multispecific synthetic competitive template was designed to amplify FGFR1-4 homologous stretches and constructed to contain FGFR1/FGFR2/FGFR3/FGFR4/GAPDH tandemly arranged forward and reverse primers that allow competition for cDNA-specific primer annealing. The housekeeping GAPDH transcript was utilized as a reference for comparing the expression profiles of different RNA pools. The assay herein described allows the comparison of relative FGFR expression levels, both within a single RNA pool and among multiple RNA pool samples. The major advantages of such a PCR-based approach are its ability to obtain unbiased FGFR mRNA expression patterns and to detect transcripts present in low copy number. Qualitative and semiquantitative analyses of the FGFR1-4 transcript repertoire in mesenchymal- and epithelial-derived primary cell cultures and cell lines demonstrated the utility of such a method to investigate the FGFR1-4 functional role in FGF signal transduction.

Fibroblast growth factor receptor mutational screening in newborns affected by metopic synostosis.

A number of craniosynostotic disorders have recently been ascribed to mutations in genes coding for the fibroblast growth factor receptors(FGFRs). The common feature of these FGFR-associated conditions is the unilateral or bilateral premature ossification of the coronal suture. One distinct craniosynostotic condition is trigonocephaly, which results from the premature fusion of the metopic suture. Trigonocephaly mostly occurs as isolated cranial defect; however, the premature closure of the metopic suture may represent a feature of more complex craniosynostotic conditions in which a progressive involvement of other cranial sutures with age is observed. The possible involvement of mutated FGFRs in trigonocephaly was investigated in nine newborns affected by isolated premature synostosis of the metopic suture. All except one of these cases carried no mutations in the FGFR1-3 domains indicated as hot spots for craniosynostosis-associated mutations. A T(978)C transition in the FGFR2 exon IIIa was found in a patient who had a phenotype that apparently fitted the trigonocephalic condition at birth, but showed additional facial anomalies, which worsened progressively with age towards a Crouzon-like profile. The present finding points out the importance, from both diagnostic and prognostic points of view, of early FGFR mutational screening in craniosynostotic conditions, even in forms that apparently do not involve closure of the coronal suture at birth.

Decreased proliferation and altered differentiation in osteoblasts from genetically and clinically distinct craniosynostotic disorders.

Craniosynostoses are a heterogeneous group of disorders characterized by premature fusion of cranial sutures. Mutations in fibroblast growth factor receptors (FGFRs) have been associated with a number of such conditions. Nevertheless, the cellular mechanism(s) involved remain unknown. We analyzed cell proliferation and differentiation in osteoblasts obtained from patients with three genetically and clinically distinct craniosynostoses: Pfeiffer syndrome carrying the FGFR2 C342R substitution, Apert syndrome with FGFR2 P253R change, and a nonsyndromic craniosynostosis without FGFR canonic mutations, as compared with control osteoblasts. Osteoblasts from craniosynostotic patients exhibited a lower proliferation rate than control osteoblasts. P253R and nonsyndromic craniosynostosis osteoblasts showed a marked differentiated phenotype, characterized by high alkaline phosphatase activity, increased mineralization and expression of noncollagenous matrix proteins, associated with high expression and activation of protein kinase Calpha and protein kinase Cepsilon isoenzymes. By contrast, the low proliferation rate of C342R osteoblasts was not associated with a differentiated phenotype. Although they showed higher alkaline phosphatase activity than control, C342R osteoblasts failed to mineralize and expressed low levels of osteopontin and osteonectin and high protein kinase Czeta levels. Stimulation of proliferation and inhibition of differentiation were observed in all cultures on FGF2 treatment. Our results suggest that an anticipated proliferative/differentiative switch, associated with alterations of the FGFR transduction pathways, could be the causative common feature in craniosynostosis and that mutations in distinct FGFR2 domains are associated with an in vitro heterogeneous differentiative phenotype.

Detection of bovine mitochondrial DNA in ruminant feeds: a molecular approach to test for the presence of bovine-derived materials.

A ban on ruminant-derived proteins in ruminant feeds has been introduced as a preventive measure to avoid the spread of bovine spongiform encephalopathy (BSE), as well as to minimize any potential risk of BSE transmission from bovines to humans. In the absence of commercially available efficient methods for identification of bovine-derived proteins in animal feeds, we developed a rapid and sensitive polymerase chain reaction (PCR)-based assay which allows detection and identification of a bovine-specific mitochondrial DNA sequence from feedstuffs. The amplified product encodes for the whole ATPase subunit 8 and the amino-terminal portion of the ATPase subunit 6 proteins, which are known to exhibit a relatively low degree of conservation among vertebrates. The specific amplification of such a bovine mitochondrial sequence from reference feedstuff samples was demonstrated by means of both direct sequencing and single-strand conformational analysis of the PCR product. Specificity was also confirmed by the absence of detectable homologous PCR product when using reference feedstuff samples lacking bovine-derived meat and bonemeals, or genomic DNA samples from vertebrates whose offals are commonly included in animal feeds. This method allows detection of the presence of bovine mitochondrial DNA in feedstuffs containing less than 0.125% of bovine-derived meat and bonemeals. Furthermore, it does not appear to be considerably affected by prolonged heat treatment. DpnII and SspI restriction endonuclease digestions of the unpurified PCR product may be used routinely to confirm the bovine origin of the amplified sequence. Since this method is specific, rapid, and sensitive, it could be successfully utilized as a routine control assay to evaluate the presence of bovine-derived meat and bonemeals in ruminant feeds.

Analysis of HIV-1 Tat effects in Xenopus laevis embryos.

Tat is one of the regulatory proteins of the HIV-1 virus. To date, besides the transactivation activity, a myriad of effects exerted by HIV-1 Tat on cellular and viral genes have been observed. The present study investigated the in vivo effects of HIV-1 Tat protein in the Xenopus embryo. We adopted the Xenopus system since expression of putative regulatory factors in the embryo has been widely used as a quick and effective first screen for protein function. Xenopus' early development is well characterized by stage-specific phenotypes, therefore, an in vivo HIV-1 Tat-mediated aberrant phenotype can easily be detected and analyzed. HIV-1 Tat protein expression through injection of synthetic mRNA into zygotes produced a marked delay in gastrulation leading to altered specification of the anterior-posterior axis and to partial or total loss of anterior structures. HIV-1 Tat effects resulted in a general suppression of gene expression, including that of Xbra and gsc, two early genes whose expression is required for proper gastrulation. The specificity of Tat effects was demonstrated by injecting a 'loss of function' mutant (Tat-C37S), lacking a single cysteine residue, which did not yield any effect. Both Tat and Tat-C37S were found to be localized mainly in the nucleus. The importance of subcellular targeting for the effects caused by HIV-1 Tat was demonstrated by injecting a second mutant (Tat-BDM), carrying an altered nuclear localization signal sequence. The Tat-BDM protein localized in the cytoplasm and accumulated at the cell membrane. Embryos injected with Tat-BDM mRNA did not develop beyond gastrulation. The importance of proper protein conformation and subcellular localization in determining Tat effects is discussed.

The uvp1 gene on the R46 plasmid encodes a resolvase that catalyzes site-specific resolution involving the 5'-conserved segment of the adjacent integron In1.

The product of the uvp1 gene of the R46 plasmid, a member of the DNA invertase-resolvase family, was studied to characterize its recombination activity on the R46 plasmid. The purified Uvp1 protein specifically binds to a 256-bp DNA fragment located immediately upstream of the uvp1 gene itself, and overlapping the 5'-conserved segment (5'-CS) of the R46 integron In1. We identified on this fragment a putative resolution (res) site. Using an in vitro assay, we demonstrated the ability of the protein to resolve a synthetic cointegrate containing a direct repeat of the res site. In vivo, we obtained cointegrate resolution in Uvp1-expressing recA- cells. Sites I and II, subsites of the putative res site, lie within the outer boundary of the integron 5'-CS which is common to all the known integrons. Furthermore, a 69-bp DNA element (containing site I) is required for cointegrate resolution. We propose that this recombination mechanism protects R46 plasmid against unequal distribution following fusion with either identical or different integron-bearing plasmids. Moreover, Uvp1 might have a role in generating gene cassette diversity between the two conserved segments of the integron.

Trp290Cys mutation in exon IIIa of the fibroblast growth factor receptor 2 (FGFR2) gene is associated with Pfeiffer syndrome.

Pfeiffer syndrome is a skeletal disorder characterized by craniosynostosis associated with foot and hand anomalies. Mutations in the genes encoding fibroblast growth factor receptors 1 and 2 (FGFR1 and FGFR2) have recently been implicated in the aetiology of such a syndrome, as well as of other craniosynostotic conditions. We now report a novel missense mutation, a G to C transversion at position 1049 (exon IIIa) of FGFR2, detected in a patient with severe Pfeiffer clinical features. The mutation results in the substitution of a cysteine for tryptophan-290 in the third immunoglobulin-like domain and affects both spliceoforms of FGFR2. Mutations causing replacement of tryptophan-290 have also been reported previously in Crouzon syndrome, a similar but clinically distinct craniosynostotic disorder. This finding confirms the involvement of mutations of FGFR2 exon IIIa in Pfeiffer syndrome, and emphasizes both the extensive heterogeneity of the FGFR2 mutations that result in the Pfeiffer phenotype and the perturbations caused by unpaired cysteine residues in receptor dimerization and transduction of the FGFs signal.

Jackson-Weiss syndrome: identification of two novel FGFR2 missense mutations shared with Crouzon and Pfeiffer craniosynostotic disorders.

Jackson-Weiss syndrome is a rare skeletal disorder characterized by craniosynostosis associated with foot malformations. This condition is inherited as an autosomal dominant trait with complete penetrance and wide phenotypic heterogeneity. Mutations in the fibroblast growth factor receptor 2 (FGFR2) gene have been recently identified as causes of this syndrome and of at least four other craniosynostotic disorders, namely the Apert, Beare-Stevenson cutis gyrata, Crouzon and Pfeiffer syndromes. We report two novel FGFR2 missense mutations associated with phenotypes consistent with Jackson-Weiss syndrome. Both nucleotide changes predict a serine for cysteine-342 substitution in the second half of the third immunoglobulin-like domain. The replacement of Cys342 with arginine has previously been reported in one of the three Jackson-Weiss cases investigated. Interestingly, both Cys342Ser and Cys342Arg substitutions have been found to be associated with the Crouzon and Pfeiffer phenotypes; a phenotypic heterogeneity, Crouzon vs Jackson-Weiss clinical features, has been also observed for Gln289Pro and Ala344Gly amino-acid changes. This finding indicates the genetic homogeneity of the "heterogeneous" Jackson-Weiss phenotype and a common molecular basis for these apparently "clinically distinct" craniosynostotic disorders.

Interactions among the bHLH domains of the proteins encoded by the Enhancer of split and achaete-scute gene complexes of Drosophila.

The Enhancer of split and achaete-scute gene complexes [E(spl)-C and AS-C] encode helix-loop-helix proteins required for neurogenesis in Drosophila. Using a heterologous bacterial system, we show that (i) the bHLH domains of the proteins encoded by the two gene complexes differ in their ability to form homo- and/or heterodimers; (ii) the bHLH domains of the E(spl)-C proteins m5, m7 and m8 interact with the bHLH domains of the Ac and Sc proteins. These bHLH domains form an interaction network which may represent the molecular mechanism whereby the competent state of the proneural cells is maintained until the terminal determination to neuroblast occurs. Also, the pattern of interactions of the bHLH domains of certain proteins encoded by the two gene complexes may explain their functional redundancy.

A novel approach to protein-protein interaction: complex formation between the p53 tumor suppressor and the HIV Tat proteins.

By using a novel genetic approach, based on the properties of lambda cl repressor, we demonstrate that the HIV-1 Tat protein specifically interacts with the human p53 protein via the p53 O2 dimerization domain. By random and site-specific mutagenesis, we also identify the residues in Tat and O2 peptides which are involved in this interaction. Two alternative biological consequences are expected to result from Tat-p53 interaction: (i) Tat-O2 interaction inactivates p53 regulation function, thus producing cell transformation; (ii) Tat-O2 interaction favours the formation of p53 dimers, thus leading the cell towards apoptosis.

Genetic tests to reveal TAT homodimer formation and select TAT homodimer inhibitor.

The HIV Tat protein is essential for productive infection and is a potent activator of viral gene expression. By constructing a genetic fusion between the amino-terminal DNA-binding domain of the lambda repressor (as a reporter for dimerization) and Tat, we show that Tat forms dimers in vivo. By deletion analysis and site-directed mutagenesis, we show that (i) the peptide encoded by exon-1 of Tat is sufficient to promote dimerization and (ii) cys37 is essential for homo-dimerization of Tat protein. Furthermore, by using a new E. coli strain in which the expression of beta-galactosidase is under the negative control of the cl::Tat repressor, we select a protein (CD10/Nep) expressed by human Jurkat T-cells which inhibits Tat dimerization.

pR plasmid replication provides evidence that single-stranded DNA induces the SOS system in vivo.

Evidence is presented that the pR bat gene is essential for plasmid replication and for spontaneous induction of the SOS response in Escherichia coli. Mutations preventing single-stranded DNA production, needed for pR plasmid replication, also prevent the induction of the SOS system. The following experimental design was used. Firstly, we identified the minima rep region, defined as the minimal DNA sequence necessary for pR plasmid replication and, secondly, analyzed the nucleotide sequence of this region. This identified structures and functions (ori-plus, ori-minus and Rep protein) homologous to those found in phages and plasmids replicating by the rolling-circle mechanism. Finally, mutations were introduced either in the replication protein catalytic site or in the nick site consensus sequence, which caused the pR plasmid to lose its ability to induce the SOS system. We conclude that, in this system, the in vivo SOS-inducing signal appears to be the single-stranded DNA produced during pR replication.

The uvp1 gene of plasmid pR cooperates with mucAB genes in the DNA repair process.

We show that a DNA fragment that contains the uvp1 gene of the plasmid pR directs the synthesis in Escherichia coli minicells of a protein of apparent molecular weight 20 kDa. Inspection of the nucleotide sequence of the region reveals an open reading frame that has the capacity to encode a protein of 198 amino acids. The uvp1 gene product has been found, in two different systems, to enhance the recombinational activity of E. coli cells. We have also observed a striking similarity to resolvase and invertase proteins. The significance of this finding for the function of the uvp1 gene product requires further investigation. We conclude that the uvp1 gene encodes a 20 kDa protein which appears to be responsible for enhancement of both UV survival and recombinational activity in E. coli.

The pR plasmid: a tool for studying DNA repair and mutagenesis in prokaryotic and eukaryotic cells.

The pR plasmid, a derivative of R46 plasmid, offers the possibility to have an experimental approach to three important problems related to UV repair and mutagenesis. By using this plasmid we were able to show: a) the pR mucAB genes need the cooperation of uvpl gene product to carry out their UV repair function; b) the expression of mucAB genes is regulated not only by lexA gene, but by a gene localized in the rep region of pR itself. This gene acts as an antirepressor of lexA; c) mammalian cells show an enhanced resistance to UV light when transformed by pR plasmid carrying the mucAB genes.

Bent helical structure in Trypanosoma lewisi minicircles.

By gel retardation assay and computational analysis we demonstrated a bent region in Trypanosoma lewisi, localized in two different classes of minicircles. We showed that in each minicircle this bent region is unique, adjacent to one of two highly conserved regions and characterized by adenine stretches. The same properties are conserved in the majority of minicircles from Trypanosomes tested so far. Therefore, we suggest that the genetic information could be located in a definite structure of minicircle DNA molecules rather than in the nucleotide sequence.

The rep region of pR plasmid regulates the expression of SOS system.

By using an artificial hybrid between phage lambda and the pR plasmid, we have shown that the rep region of the pR plasmid encodes a function which regulates the expression of the muc genes (plasmid genes that are under the negative control of lexA and responsible for an increased rate of spontaneous mutagenesis and resistance to UV and chemicals). Expression of the muc genes were monitored by a fusion between the muc promoter and the lacZ structural gene. When E. coli cells containing such a fusion are infected by the hybrid lambda pR phasmid, beta-galactosidase activity is enhanced, indicating that pR encodes an antagonist of lexA. By deletion mapping we have located the gene encoding the antagonist of lexA (bat) in the rep region of the plasmid. The bat gene product can also antagonize the lambda cI repressor as shown by the observation that lambda pR phasmids are virulent on a homoimmune lysogen. We have exploited this latter property to carry out genetic and functional analysis of the bat region. This region is organized as a classical operon where the expression of the bat structural gene is negatively regulated by a repressor gene that encodes a proteic product.

Cellular response to DNA damage is enhanced by the pR plasmid in mouse cells and in Escherichia coli.

The pR plasmid, which enhances the survival of Escherichia coli C600 exposed to UV light by induction of the SOS regulatory mechanism, showed the same effect when it transformed mouse LTA cells (tk-, aprt-). With Tn5 insertion mutagenesis which inactivates UV functions in the pR plasmid, we recognized two different regions of the plasmid, uvp1 and uvp2. These pR UVR- mutants exhibited the same effect in LTA transformed cells, demonstrating that resistance to UV light, carried by the pR plasmid, was really due to the expression of these two regions, which were also in the mouse cells. Statistical analysis showed that the expression of the uvp1 and uvp2 regions significantly increased (P less than 0.01) the survival upon exposure to UV light in mouse cells and bacteria. These results might suggest the presence of an inducible repair response to DNA damage in mouse LTA cells.