Drosophila mir-9a regulates wing development via fine-tuning expression of the LIM only factor, dLMO.

MicroRNAs are short non-coding endogenous RNAs that are implicated in regulating various aspects of plants and animal development, however their functions in organogenesis are largely unknown. Here we report that mir-9a belonging to the mir-9 family, regulates Drosophila wing development through a functional target site in the 3' untranslated region of the Drosophila LIM only protein, dLMO. dLMO is a transcription cofactor, that directly inhibits the activity of Apterous, the LIM-HD factor required for the proper dorsal identity of the wings. Deletions of the 3' untranslated region, including the mir-9a site, generate gain-of-function dLMO mutants (Beadex) associated with high levels of dLMO mRNA and protein. Beadex mutants lack wing margins, a phenotype also observed in null mir-9a mutants. We found that mir-9a and dLMO are co-expressed in wing discs and interact genetically for controlling wing development. Lack of mir-9a results in overexpression of dLMO, while gain-of-function mir-9a mutant suppresses dLMO expression. These data indicate that a function of mir-9a is to ensure the appropriate stoichiometry of dLMO during Drosophila wing development. The mir-9a binding site is conserved in the human counterpart LMO2, the T-cell acute leukemia oncogene, suggesting that mir-9 might apply a similar strategy to maintain LMO2 expression under a detrimental threshold.

Drosophila C-terminal binding protein, dCtBP is required for sensory organ prepattern and sharpens proneural transcriptional activity of the GATA factor Pnr.

The peripheral nervous system is required for animals to detect and to relay environmental stimuli to central nervous system for the information processing. In Drosophila, the precise spatial and temporal expression of two proneural genes achaete (ac) and scute (sc), is necessary for development of the sensory organs. Here we present an evidence that the transcription co-repressor, dCtBP acts as a negative regulator of sensory organ prepattern. Loss of dCtBP function mutant exhibits ectopic sensory organs, while overexpression of dCtBP results in a dramatic loss of sensory organs. These phenotypes are correlated with mis-emerging of sensory organ precursors and perturbated expression of proneural transcription activator Ac. Mammalian CtBP-1 was identified via interaction with the consensus motif PXDLSX(K/R) of adenovirus E1A oncoprotein. We demonstrated that dCtBP binds directly to PLDLS motif of Drosophila Friend of GATA-1 protein, U-shaped and sharpens the adult sensory organ development. Moreover, we found that dCtBP mediates multivalent interaction with the GATA transcriptional activator Pannier and acts as a direct co-repressor of the Pannier-mediated activation of proneural genes. We demonstrated that Pannier genetically interacts with dCtBP-interacting protein HDAC1, suggesting that the dCtBP-dependent regulation of Pannier activity could utilize a repressive mechanism involving alteration of local chromatine structure.

Drosophila dLMO-PA isoform acts as an early activator of achaete/scute proneural expression.

The Drosophila bHLH proneural factors Achaete (Ac) and Scute (Sc) are expressed in clusters of cells (proneural clusters), providing the cells with the potential to develop a neural fate. Mediodorsal proneural patterning is mediated through the GATA transcription factor Pannier (Pnr) that activates ac/sc directly through binding to the dorsocentral (DC) enhancer of ac/sc. Besides, the Gfi transcription factor Senseless (Sens), a target of Ac/Sc, synergizes with ac/sc in the presumptive sensory organ precursors (SOPs). Here we investigate, through new genetic tools, the function of dLMO, the Drosophila LIM only transcription factor that was already known to control wing development. We show that dLMO gene encodes two isoforms, dLMO-RA and dLMO-RB. dLMO null and dLMO-RA(-) deletions have similar phenotypes, lacking thoracic and wing margin sensory organs (SO), while dLMO-RB(-) deletion has normal SOs. At early stages, dLMO-RA is expressed in proneural clusters, however later it is excluded from the SOPs. We found that dLMO functions as a Pnr coactivator to promote ac/sc expression. In the late SOPs, where dLMO-PA is not expressed, Pnr participates to the Sens-dependent regulation of ac/sc. Taken together these results suggest that dLMO-PA is the major isoform that is required for early activation of ac/sc expression.

The Rosa genome provides new insights into the domestication of modern roses.

Roses have high cultural and economic importance as ornamental plants and in the perfume industry. We report the rose whole-genome sequencing and assembly and resequencing of major genotypes that contributed to rose domestication. We generated a homozygous genotype from a heterozygous diploid modern rose progenitor, Rosa chinensis 'Old Blush'. Using single-molecule real-time sequencing and a meta-assembly approach, we obtained one of the most comprehensive plant genomes to date. Diversity analyses highlighted the mosaic origin of 'La France', one of the first hybrids combining the growth vigor of European species and the recurrent blooming of Chinese species. Genomic segments of Chinese ancestry identified new candidate genes for recurrent blooming. Reconstructing regulatory and secondary metabolism pathways allowed us to propose a model of interconnected regulation of scent and flower color. This genome provides a foundation for understanding the mechanisms governing rose traits and should accelerate improvement in roses, Rosaceae and ornamentals.

Precocious expression of the Glide/Gcm glial-promoting factor in Drosophila induces neurogenesis.

Neurons and glial cells depend on similar developmental pathways and often originate from common precursors; however, the differentiation of one or the other cell type depends on the activation of cell-specific pathways. In Drosophila, the differentiation of glial cells depends on a transcription factor, Glide/Gcm. This glial-promoting factor is both necessary and sufficient to induce the central and peripheral glial fates at the expense of the neuronal fate. In a screen for mutations affecting the adult peripheral nervous system, we have found a dominant mutation inducing supernumerary sensory organs. Surprisingly, this mutation is allelic to glide/gcm and induces precocious glide/gcm expression, which, in turn, activates the proneural genes. As a consequence, sensory organs are induced. Thus, temporal misregulation of the Glide/Gcm glial-promoting factor reveals a novel potential for this cell fate determinant. At the molecular level, this implies unpredicted features of the glide/gcm pathway. These findings also emphasize the requirement for both spatial and temporal glide/gcm regulation to achieve proper cell specification within the nervous system.

Biodiversity and noncanonical Notch signaling.

Early genetics in flies revealed that Notch is a complex pleiotropic locus. We now know that Notch is a receptor that plays prominent roles during development and functions locally in many tissues to instruct cell fate decisions. Drosophila has been an excellent model to identify genetically the elements that contribute to the canonical Notch signaling transduction machinery defined as DSL-Notch-CSL-MAML axis. This core pathway is required in many biological events in all animals. Though the canonical Notch pathway is relatively simple, and as the steps of the events are now more deeply understood, an increasing number of reports in the last decade show that many other molecules can influence Notch signaling, some by competing with a given element of the cascade. This may occur at any step bringing more diversity and plasticity to the Notch pathway. Most of these regulatory molecules act in a context-specific manner and/or are themselves key regulators in other pathways, providing increasing examples of how connections among distinct pathway modulate each other ("cross talk"). The noncanonical signals discussed in this chapter are broadly defined and correspond to the following: DSL-independent activations, interactions with non-DSL ligands, CSL-independent signaling, signal transduction without cleavage, differential posttranslational modifications, competition/protection for a cofactor, and cross talk with other signaling pathways [Wnt, bone morphogenic protein (BMP), NF-kappaB, etc.]. Though some deemed controversial, these events may impact human diseases. Understanding the molecular nature of these events will allow avoidance of adverse effects during possible clinical treatments. In this review, we will focus on some noncanonical Notch activities and their in vivo significance during developmental and pathological processes.

The Drosophila LIM-homeo domain protein Islet antagonizes pro-neural cell specification in the peripheral nervous system.

The pattern of the external sensory organs (SO) in Drosophila depends on the activity of the basic helix-loop-helix (bHLH) transcriptional activators Achaete/Scute (Ac/Sc) that are expressed in clusters of cells (pro-neural clusters) and provide the cells with the potential to develop a neural fate. In the mesothorax, the GATA1 transcription factor Pannier (Pnr), together with its cofactor Chip, activates ac/sc genes directly through binding to the dorso-central enhancer (DC) of ac/sc. We identify the LIM-homeo domain (LIM-HD) transcription factor Islet (Isl) by genetic screening and investigate its role in the thoracic pre-patterning. We show that isl loss-of-function mutations result in expanded Ac expression in DC and scutellar (SC) pro-neural clusters and formation of ectopic sensory organs. Overexpression of Isl decreases pro-neural expression and suppresses bristle development. Moreover, Isl is coexpressed with Pnr in the posterior region of the mesothorax. In the DC pro-neural cluster, Isl antagonizes Pnr activity both by dimerization with the DNA-binding domain of Pnr and via competitive inhibition of the Chip-bHLH interaction. We propose that sensory organ pre-patterning relies on the antagonistic activity of individual Chip-binding factors. The differential affinities of these binding-factors and their precise stoichiometry are crucial in specifying pre-patterns within the different pro-neural clusters.

Enhancer-promoter communication mediated by Chip during Pannier-driven proneural patterning is regulated by Osa.

The GATA factor Pannier activates proneural achaete/scute (ac/sc) expression during development of the sensory organs of Drosophila through enhancer binding. Chip bridges Pannier with the (Ac/Sc)-Daughterless heterodimers bound to the promoter and facilitates the enhancer-promoter communication required for proneural development. We show here that this communication is regulated by Osa, which is recruited by Pannier and Chip. Osa belongs to Brahma chromatin remodeling complexes and we show that Osa negatively regulates ac/sc. Consequently, Pannier and Chip also play an essential role during repression of proneural gene expression. Our study suggests that altering chromatin structure is essential for regulation of enhancer-promoter communication.