Thomas Brody

FlyExpress: visual mining of spatiotemporal patterns for genes and publications in Drosophila embryogenesis

SUMMARY Images containing spatial expression patterns illuminate the roles of different genes during embryogenesis. In order to generate initial clues to regulatory interactions, biologists frequently need to know the set of genes expressed at the same time at specific locations in a developing embryo, as well as related research publications. However, text-based mining of image annotations and research articles cannot produce all relevant results, because the primary data are images that exist as graphical objects. We have developed a unique knowledge base (FlyExpress) to facilitate visual mining of images from Drosophila melanogaster embryogenesis. By clicking on specific locations in pictures of fly embryos from different stages of development and different visual projections, users can produce a list of genes and publications instantly. In FlyExpress, each queryable embryo picture is a heat-map that captures the expression patterns of more than 4500 genes and more than 2600 published articles. In addition, one can view spatial patterns for particular genes over time as well as find other genes with similar expression patterns at a given developmental stage. Therefore, FlyExpress is a unique tool for mining spatiotemporal expression patterns in a format readily accessible to the scientific community. AVAILABILITY http://www.flyexpress.net CONTACT s.kumar@asu.edu.

Horizontal Gene Transfers Link a Human MRSA Pathogen to Contagious Bovine Mastitis Bacteria

Background Acquisition of virulence factors and antibiotic resistance by many clinically important bacteria can be traced to horizontal gene transfer (HGT) between related or evolutionarily distant microflora. Comparative genomic analysis has become an important tool for identifying HGT DNA in emerging pathogens. We have adapted the multi-genome alignment tool EvoPrinter to facilitate discovery of HGT DNA sequences within bacterial genomes and within their mobile genetic elements. Principal Findings EvoPrinter analysis of 13 different Staphylococcus aureus genomes revealed that one of the human isolates, the hospital epidemic methicillin-resistant MRSA252 strain, uniquely shares multiple putative HGT DNA sequences with different causative agents of bovine mastitis that are not found in the other human S. aureus isolates. MRSA252 shares over 14 different DNA sequence blocks with the bovine mastitis ET3 S. aureus strain RF122, and many of the HGT DNAs encode virulence factors. EvoPrinter analysis of the MRSA252 chromosome also uncovered virulence-factor encoding HGT events with the genome of Listeria monocytogenes and a Staphylococcus saprophyticus associated plasmid. Both bacteria are also causal agents of contagious bovine mastitis. Conclusions EvoPrinter analysis reveals that the human MRSA252 strain uniquely shares multiple DNA sequence blocks with different causative agents of bovine mastitis, suggesting that HGT events may be occurring between these pathogens. These findings have important implications with regard to animal husbandry practices that inadvertently enhance the contact of human and livestock bacterial pathogens.

Rapid detection and curation of conserved DNA via enhanced-BLAT and EvoPrinterHD analysis

BackgroundMulti-genome comparative analysis has yielded important insights into the molecular details of gene regulation. We have developed EvoPrinter, a web-accessed genomics tool that provides a single uninterrupted view of conserved sequences as they appear in a species of interest. An EvoPrint reveals with near base-pair resolution those sequences that are essential for gene function.ResultsWe describe here EvoPrinterHD, a 2nd-generation comparative genomics tool that automatically generates from a single input sequence an enhanced view of sequence conservation between evolutionarily distant species. Currently available for 5 nematode, 3 mosquito, 12 Drosophila, 20 vertebrate, 17 Staphylococcus and 20 enteric bacteria genomes, EvoPrinterHD employs a modified BLAT algorithm [enhanced-BLAT (eBLAT)], which detects up to 75% more conserved bases than identified by the BLAT alignments used in the earlier EvoPrinter program. The new program also identifies conserved sequences within rearranged DNA, highlights repetitive DNA, and detects sequencing gaps. EvoPrinterHD currently holds over 112 billion bp of indexed genomes in memory and has the flexibility of selecting a subset of genomes for analysis. An EvoDifferences profile is also generated to portray conserved sequences that are uniquely lost in any one of the orthologs. Finally, EvoPrinterHD incorporates options that allow for (1) re-initiation of the analysis using a different genomes aligning region as the reference DNA to detect species-specific changes in less-conserved regions, (2) rapid extraction and curation of conserved sequences, and (3) for bacteria, identifies unique or uniquely shared sequences present in subsets of genomes.ConclusionEvoPrinterHD is a fast, high-resolution comparative genomics tool that automatically generates an uninterrupted species-centric view of sequence conservation and enables the discovery of conserved sequences within rearranged DNA. When combined with cis-Decoder, a program that discovers sequence elements shared among tissue specific enhancers, EvoPrinterHD facilitates the analysis of conserved sequences that are essential for coordinate gene regulation.

Drosophila intermediate neural progenitors produce lineage-dependent related series of diverse neurons

Drosophila type II neuroblasts (NBs), like mammalian neural stem cells, deposit neurons through intermediate neural progenitors (INPs) that can each produce a series of neurons. Both type II NBs and INPs exhibit age-dependent expression of various transcription factors, potentially specifying an array of diverse neurons by combinatorial temporal patterning. Not knowing which mature neurons are made by specific INPs, however, conceals the actual variety of neuron types and limits further molecular studies. Here we mapped neurons derived from specific type II NB lineages and found that sibling INPs produced a morphologically similar but temporally regulated series of distinct neuron types. This suggests a common fate diversification program operating within each INP that is modulated by NB age to generate slightly different sets of diverse neurons based on the INP birth order. Analogous mechanisms might underlie the expansion of neuron diversity via INPs in mammalian brain.

Nerfin-1 and -2, novel Drosophila Zn-finger transcription factor genes expressed in the developing nervous system

To gain insight into the regulatory networks controlling Drosophila neural-identity decisions, we have identified new neuronal precursor genes by performing an in situ hybridization screen of differentially selected embryonic head cDNAs. Here, we describe the molecular characteristics and expression profile of nerfin-1, a novel pan-neural precursor gene. This paper also documents the embryonic expression of another structurally related gene, nerfin-2. During early CNS development, nerfin-1 gene expression is activated in neuroblasts (NBs) prior to lineage formation. However, after early sublineage development, nerfin-1 expression shifts from NBs to ganglion mother cells (GMCs) but is not expressed in neurons or glia. Differing from nerfin-1, nerfin-2 is expressed only in a subset of brain neurons. Possessing a conserved putative DNA-binding domain, the predicted Nerfin-1 and -2 proteins belong to a subfamily of Zn-finger transcription factors with cognates identified in nematode, mouse and man.

cis-Decoder discovers constellations of conserved DNA sequences shared among tissue-specific enhancers

A systematic approach is described for analysis of evolutionarily conserved cis-regulatory DNA using cis-Decoder, a tool for discovery of conserved sequence elements that are shared between similarly regulated enhancers. Analysis of 2,086 conserved sequence blocks (CSBs), identified from 135 characterized enhancers, reveals most CSBs consist of shorter overlapping/adjacent elements that are either enhancer type-specific or common to enhancers with divergent regulatory behaviors. Our findings suggest that enhancers employ overlapping repertoires of highly conserved core elements.

Making Drosophila lineage–restricted drivers via patterned recombination in neuroblasts

The Drosophila cerebrum originates from about 100 neuroblasts per hemisphere, with each neuroblast producing a characteristic set of neurons. Neurons from a neuroblast are often so diverse that many neuron types remain unexplored. We developed new genetic tools that target neuroblasts and their diverse descendants, increasing our ability to study fly brain structure and development. Common enhancer-based drivers label neurons on the basis of terminal identities rather than origins, which provides limited labeling in the heterogeneous neuronal lineages. We successfully converted conventional drivers that are temporarily expressed in neuroblasts, into drivers expressed in all subsequent neuroblast progeny. One technique involves immortalizing GAL4 expression in neuroblasts and their descendants. Another depends on loss of the GAL4 repressor, GAL80, from neuroblasts during early neurogenesis. Furthermore, we expanded the diversity of MARCM-based reagents and established another site-specific mitotic recombination system. Our transgenic tools can be combined to map individual neurons in specific lineages of various genotypes.

Use of a Drosophila genome‐wide conserved sequence database to identify functionally related cis‐regulatory enhancers

Background: Phylogenetic footprinting has revealed that cis‐regulatory enhancers consist of conserved DNA sequence clusters (CSCs). Currently, there is no systematic approach for enhancer discovery and analysis that takes full‐advantage of the sequence information within enhancer CSCs. Results: We have generated a Drosophila genome‐wide database of conserved DNA consisting of >100,000 CSCs derived from EvoPrints spanning over 90% of the genome. cis‐Decoder database search and alignment algorithms enable the discovery of functionally related enhancers. The program first identifies conserved repeat elements within an input enhancer and then searches the database for CSCs that score highly against the input CSC. Scoring is based on shared repeats as well as uniquely shared matches, and includes measures of the balance of shared elements, a diagnostic that has proven to be useful in predicting cis‐regulatory function. To demonstrate the utility of these tools, a temporally‐restricted CNS neuroblast enhancer was used to identify other functionally related enhancers and analyze their structural organization. Conclusions: cis‐Decoder reveals that co‐regulating enhancers consist of combinations of overlapping shared sequence elements, providing insights into the mode of integration of multiple regulating transcription factors. The database and accompanying algorithms should prove useful in the discovery and analysis of enhancers involved in any developmental process. Developmental Dynamics 241:169–189, 2012.

The cis- Regulatory Dynamics of the Drosophila CNS Determinant castor are Controlled by Multiple Sub-Pattern Enhancers

In the developing CNS, unique functional identities among neurons and glia are, in part, established as a result of successive transitions in gene expression programs within neural precursor cells. One of the temporal-identity windows within Drosophila CNS neural precursor cells or neuroblasts (NBs) is marked by the expression of a zinc-finger transcription factor (TF) gene, castor (cas). Our analysis of cis-regulatory DNA within a cas loss-of-function rescue fragment has identified seven enhancers that independently activate reporter transgene expression in specific sub-patterns of the wild-type embryonic cas gene expression domain. Most of these enhancers also regulate different aspects of cas expression within the larval and adult CNS. Phylogenetic footprinting reveals that each enhancer is made up of clusters of highly conserved DNA sequence blocks that are flanked by less-conserved inter-cluster spacer sequences. Comparative analysis of the conserved DNA also reveals that cas enhancers share different combinations of sequence elements and many of these shared elements contain core DNA-binding recognition motifs for characterized temporal-identity TFs. Intra-species alignments show that two of the sub-pattern enhancers originated from an inverted duplication and that this repeat is unique to the cas locus in all sequenced Drosophila species. Finally we show that three of the enhancers differentially require cas function for their wild-type regulatory behavior. Cas limits the expression of one enhancer while two others require cas function for full expression. These studies represent a starting point for the further analysis of cas gene expression and the TFs that regulate it.

Conserved sequence block clustering and flanking inter-cluster flexibility delineate enhancers that regulate nerfin-1 expression during Drosophila CNS development

We have identified clusters of conserved sequences constituting discrete modular enhancers within the Drosophilanerfin-1 locus. nerfin-1 encodes a Zn-finger transcription factor that directs pioneer interneuron axon guidance. nerfin-1 mRNA is detected in many early delaminating neuroblasts, ganglion mother cells and transiently in nascent neurons. The comparative genomics analysis program EvoPrinter revealed conserved sequence blocks both upstream and downstream of the transcribed region. By using the aligning regions of different drosophilids as the reference DNA, EvoPrinter detects sequence length flexibility between clusters of conserved sequences and thus facilitates differentiation between closely associated modular enhancers. Expression analysis of enhancer-reporter transgenes identified enhancers that drive expression in different regions of the developing embryonic and adult nervous system, including subsets of embryonic CNS neuroblasts, GMCs, neurons and PNS neurons. In summary, EvoPrinter facilitates the discovery and analysis of enhancers that control crucial aspects of nerfin-1 expression.