Martha Vázquez

Emerging roles of the SUMO pathway in development

Sumoylation is a reversible post-translational modification that targets a variety of proteins mainly within the nucleus, but also in the plasma membrane and cytoplasm of the cell. It controls diverse cellular mechanisms such as subcellular localization, protein–protein interactions, or transcription factor activity. In recent years, the use of several developmental model systems has unraveled many critical functions for the sumoylation system in the early life of diverse species. In particular, detailed analyses of mutant organisms in both the components of the SUMO pathway and their targets have established the importance of the SUMO system in early developmental processes, such as cell division, cell lineage commitment, specification, and/or differentiation. In addition, an increasing number of developmental proteins, including transcription factors and epigenetic regulators, have been identified as sumoylation substrates. Sumoylation acts on these targets through various mechanisms. For example, this modification has been involved in converting a transcription factor from an activator to a repressor or in regulating the localization and/or stability of numerous transcription factors. This review will summarize current information on the function of sumoylation in embryonic development in different species from yeast to mammals.

The Drosophila trithorax group gene tonalli (tna) interacts genetically with the Brahma remodeling complex and encodes an SP-RING finger protein.

The trithorax group genes are required for positive regulation of homeotic gene function. The trithorax group gene brahma encodes a SWI2/SNF2 family ATPase that is a catalytic subunit of the Brm chromatin-remodeling complex. We identified the tonalli (tna) gene in Drosophila by genetic interactions with brahma. tna mutations suppress Polycomb phenotypes and tna is required for the proper expressions of the Antennapedia, Ultrabithorax and Sex combs reduced homeotic genes. The tna gene encodes at least two proteins, a large isoform (TnaA) and a short isoform (TnaB). The TnaA protein has an SP-RING Zn finger, conserved in proteins from organisms ranging from yeast to human and thought to be involved in the sumoylation of protein substrates. Besides the SP-RING finger, the TnaA protein also has extended homology with other eukaryotic proteins, including human proteins. We show that tna mutations also interact with mutations in additional subunits of the Brm complex, with mutations in subunits of the Mediator complex, and with mutations of the SWI2/SNF2 family ATPase gene kismet. We propose that Tna is involved in postranslational modification of transcription complexes.

The NodI and NodJ proteins from Rhizobium and Bradyrhizobium strains are similar to capsular polysaccharide secretion proteins from Gram-negative bacteria

The NodI and NodJ nodulation proteins have been described in different Rhizobium and Bradyrhizobium species. The NodIJ genes belong to the nod regulon. Other genes from this regulon are involved in the biosynthesis and modification of lipo‐oligosaccharide molecule(s) which are morphogénic signals when acting on legume roots. It has been proposed that the NodI and NodJ proteins belong to a bacterial inner membrane transport system of small molecules. Nucleotide sequencing of MudII PR 13 insertions in the nodulation region of the symbiotic plasmid from a Rhizobium leguminosarum bv. phaseoli strain CE3 has revealed the presence of NodI and nodJ related sequences downstream of nodC. Computer nucleotide sequence analysis of the entire NodI and NodJ sequences from R. leguminosarum bv. viciae and Bradyrhizobium japonicum strains show that both proteins are similar to the KpsT and KpsM proteins from Escherichia coli Kl and K5 strains, to the BexB and BexA proteins from Haemophilis influenzae and to the CtrD and CtrC proteins from Neisseria meningitidis, respectively. Except for the NodI and NodJ proteins, all of them have been involved in the mechanism of secretion of polysaccharides in each of their harbouring species. On the basis of the similarity found, we propose that the NodI and the NodJ proteins could be involved in the export of a lipo‐oligosaccharide.

Role of the p53 homologue from Drosophila melanogaster in the maintenance of histone H3 acetylation and response to UV-light irradiation

It has been demonstrated that the human tumor suppressor p53 has an important role in modulating histone modifications after UV light irradiation. In this work we explored if the p53 Drosophila homologue has a similar role. Taking advantage of the existence of polytene chromosomes in the salivary glands of third instar larvae, we analyzed K9 and K14 H3 acetylation patterns in situ after UV irradiation of wild‐type and Dmp53 null flies. As in human cells, after UV damage there is an increase in H3 acetylation in wild‐type organisms. In Dmp53 mutant flies, this response is significantly affected at the K9 position. These results are similar to those found in human p53 mutant tumor cells with one interesting difference, only the basal H3 acetylation of K14 is reduced in Dmp53 mutant flies, while the basal H3‐K9 acetylation is not affected. This work shows, that the presence of Dmp53 is necessary to maintain normal H3‐K14 acetylation levels in Drosophila chromatin and that the function of p53 to maintaining histone modifications, is conserved in Drosophila and humans.

XNP/dATRX interacts with DREF in the chromatin to regulate gene expression

The ATRX gene encodes a chromatin remodeling protein that has two important domains, a helicase/ATPase domain and a domain composed of two zinc fingers called the ADD domain. The ADD domain binds to histone tails and has been proposed to mediate their binding to chromatin. The putative ATRX homolog in Drosophila (XNP/dATRX) has a conserved helicase/ATPase domain but lacks the ADD domain. In this study, we propose that XNP/dATRX interacts with other proteins with chromatin-binding domains to recognize specific regions of chromatin to regulate gene expression. We report a novel functional interaction between XNP/dATRX and the cell proliferation factor DREF in the expression of pannier (pnr). DREF binds to DNA-replication elements (DRE) at the pnr promoter to modulate pnr expression. XNP/dATRX interacts with DREF, and the contact between the two factors occurs at the DRE sites, resulting in transcriptional repression of pnr. The occupancy of XNP/dATRX at the DRE, depends on DNA binding of DREF at this site. Interestingly, XNP/dATRX regulates some, but not all of the genes modulated by DREF, suggesting a promoter-specific role of XNP/dATRX in gene regulation. This work establishes that XNP/dATRX directly contacts the transcriptional activator DREF in the chromatin to regulate gene expression.

A new peroxinectin-like gene preferentially expressed during oogenesis and early embryogenesis in Drosophila melanogaster.

Abstract. Several peroxidase isozymes have been described in Drosophila melanogaster. We describe a peroxinectin-like gene (Dpxt) in D. melanogaster. Peroxinectin is a cell-adhesive hemoperoxidase which binds superoxide dismutase and mediates blood cells attachment and spreading in the crayfish Pacifastacus leniusculus. The Dpxt predicted protein has a putative RGD-integrin binding tripeptide. The Dpxt mRNA is present in high amounts in late oogenesis and in early embryogenesis until the cellular blastoderm stage. It is virtually absent at other stages of the Drosophila life cycle, suggesting that Dpxt function is restricted to the early stages of fly development.

Molecular cloning of a Salmonella typhi LT‐like enterotoxin gene

Diarrhoea is a common event during typhoid fever; nevertheless, the possible participation of a diarrhoea‐inducing enterotoxin has not been described (Roy et al., 1985). Recombinant bacteriophage λ FDC1 was isolated from a genomic library of Salmonella typhi, the causal agent of typhoid fever, by screening with a probe for the B subunit gene of the heat‐labile, cholera‐like, Escherichia coli enterotoxin (LT). λ FDC1 codes for an enterotoxin that causes secretion in rat ileal loops, that elongates Chinese hamster ovary (CHO) cells, that is recognized by antibodies against LT, and does not bind in vitroto ganglioside GM1. These results should allow further studies towards elucidating a possible role for the S. typhi enterotoxin in the pathogenesis of typhoid fever.

Expression of nodule-specific genes in Phaseolus vulgaris L.

The identification of some nodule-specific host proteins (nodulins) from common bean (Phaseolus vulgaris L.), a tropical ureide-transporting legume, is described. Particularly, the existence and developmental expression of several abundant nodule-specific transcripts of P. vulgaris are shown, including leghemoglobin, nodulespecific uricase and a group that in vitro translates into a cluster of about 30 kDa products. The expression pattern of nodulins in effective (Fix+) nodules compared to ineffective (Fix-) ones is also presented. The modified expression of main nodulins observed between these nodules indicates that different levels and/or factors associated with their regulation are involved. The intracellular infection by Rhizobium as a decisive step in the induction of some P. vulgaris nodulins is discussed.

Characterization of Rhizobium phaseoli Sym plasmid regions involved in nodule morphogenesis and host‐range specificity

Two nodulation regions from the symbiotic plasmid (pSym) of Rhizobium phaseoil CE‐3 were identified. The two regions were contained in overlapping cosmids pSM927 and pSM991. These cosmids, in a R phaseoli pSym‐cured strain background, induced ineffective nodules on Phaseolus vulgaris roots.

Physical and Functional Interactions between Drosophila Homologue of Swc6/p18Hamlet Subunit of the SWR1/SRCAP Chromatin-remodeling Complex with the DNA Repair/Transcription Factor TFIIH

Background: TFIIH interacts with multiple factors. Results: The fly p8 subunit of TFIIH is encoded in a bicistronic transcript with the homolog of the Swc6/p18Hamlet subunit of the SWR1/SRCAP complex and physically and genetically interacts with TFIIH. Conclusion: There is a functional link between Swc6/p18Hamlet and TFIIH. Significance: This functional interaction opens new avenues to study how TFIIH modulates transcription and DNA repair. The multisubunit DNA repair and transcription factor TFIIH maintains an intricate cross-talk with different factors to achieve its functions. The p8 subunit of TFIIH maintains the basal levels of the complex by interacting with the p52 subunit. Here, we report that in Drosophila, the homolog of the p8 subunit (Dmp8) is encoded in a bicistronic transcript with the homolog of the Swc6/p18Hamlet subunit (Dmp18) of the SWR1/SRCAP chromatin remodeling complex. The SWR1 and SRCAP complexes catalyze the exchange of the canonical histone H2A with the H2AZ histone variant. In eukaryotic cells, bicistronic transcripts are not common, and in some cases, the two encoded proteins are functionally related. We found that Dmp18 physically interacts with the Dmp52 subunit of TFIIH and co-localizes with TFIIH in the chromatin. We also demonstrated that Dmp18 genetically interacts with Dmp8, suggesting that a cross-talk might exist between TFIIH and a component of a chromatin remodeler complex involved in histone exchange. Interestingly, our results also show that when the level of one of the two proteins is decreased and the other maintained, a specific defect in the fly is observed, suggesting that the organization of these two genes in a bicistronic locus has been selected during evolution to allow co-regulation of both genes.