Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts

Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to Oct 20 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.Comment: 17 pages. This version (v2) includes two tables and 1 section not included in v1. Accepted for publication in Astronomy & Astrophysic

Non-gonadal somatic piRNA pathways ensure sexual differentiation, larval growth, and wing development in silkworms.

PIWI-interacting RNAs (piRNAs) guide PIWI proteins to target transposons in germline cells, thereby suppressing transposon activity to preserve genome integrity in metazoans' gonadal tissues. Piwi, one of three Drosophila PIWI proteins, is expressed in the nucleus and suppresses transposon activity by forming heterochromatin in an RNA cleavage-independent manner. Recently, Piwi was reported to control cell metabolism in Drosophila fat body, providing an example of piRNAs acting in non-gonadal somatic tissues. However, mutant flies of the other two PIWI proteins, Aubergine (Aub) and Argonaute3 (Ago3), show no apparent phenotype except for infertility, blurring the importance of the piRNA pathway in non-gonadal somatic tissues. The silkworm, Bombyx mori, possesses two PIWI proteins, Siwi (Aub homolog) and BmAgo3 (Ago3 homolog), whereas B. mori does not have a Piwi homolog. Siwi and BmAgo3 are mainly expressed in gonadal tissues and play a role in repressing transposon activity by cleaving transposon RNA in the cytoplasm. Here, we generated Siwi and BmAgo3 loss-of-function mutants of B. mori and found that they both showed delayed larval growth and failed to become adult moths. They also exhibited defects in wing development and sexual differentiation. Transcriptome analysis revealed that loss of somatic piRNA biogenesis pathways results in abnormal expression of not only transposons but also host genes, presumably causing severe growth defects. Our results highlight the roles of non-gonadal somatic piRNAs in B. mori development

Dysregulation of global gene expression in the whole body in <i>BmAgo3</i> and <i>Siwi</i> KO.

(A) Transposon derepression by BmAgo3 and Siwi KO. RNA-seq libraries were prepared from total RNA extracted from the whole body of two third instar larvae. MAplots were created using the average of triplicate repeats compared to the WT. Each dot indicates a transposon; red dots indicate transposons at M (y-axis) > 1 and A (x-axis) > 0 in BmAgo3 KO females. The axes show: A (x-axis) = (log2(TPM in KO) + log2(TPM in WT))/2. M (y-axis) = log2(TPM in KO)–log2(TPM in WT). Derepressed transposons in BmAgo3 KO females were also depressed in Siwi KO females and in Siwi and BmAgo3 KO males. (B) Differentially expressed genes (DEGs) in BmAgo3 and Siwi KO larvae. MAplots were created using the average of triplicate repeats compared to the WT. Each dot indicates a gene; magenta dots indicate DEGs with variable expression at false discovery rate (FDR) of 56]. (C) Expression patterns of genes showing statistically significant expression changes in any comparisons (magenta dots in (B)). TPMs of all DEGs in BmAgo3 and Siwi KO larvae indicated by magenta dots in (B) were normalized by Z-score and clustered into six major clusters using Heatplus R package. (D) Plots of Z-scores of genes belonging to each of the six clusters. Three plots per gene are shown as they were analyzed in triplicate. The bar graph shows the average ± SD of all points.</p

Developmental delay in <i>BmAgo3</i> and <i>Siwi</i> KO mutant larvae.

(A) The third instar larvae of BmAgo3 KO mutants. (B) The third instar larvae of Siwi KO mutants. About a quarter of larvae exhibited developmental delay at the larval stage. Scale bars, 1 cm. (TIF)</p

GO analysis of tissue-specific genes in <i>BmAgo3</i> KO larvae.

(A and B) GO analysis for molecular function (A) and biological process (B) in the fat body (FB) and wing discs (WD). Bonferroni-adjusted p values (–log10) and selected gene numbers in each GO are shown by gray bars and yellow circles, respectively. (TIF)</p