Observation of contemporaneous optical radiation from a gamma-ray burst

The origin of gamma-ray bursts (GRBs) has been enigmatic since their discovery. The situation improved dramatically in 1997, when the rapid availability of precise coordinates for the bursts allowed the detection of faint optical and radio afterglows - optical spectra thus obtained have demonstrated conclusively that the bursts occur at cosmological distances. But, despite efforts by several groups, optical detection has not hitherto been achieved during the brief duration of a burst. Here we report the detection of bright optical emission from GRB990123 while the burst was still in progress. Our observations begin 22 seconds after the onset of the burst and show an increase in brightness by a factor of 14 during the first 25 seconds; the brightness then declines by a factor of 100, at which point (700 seconds after the burst onset) it falls below our detection threshold. The redshift of this burst, approximately 1.6, implies a peak optical luminosity of 5 times 10^{49} erg per second. Optical emission from gamma-ray bursts has been generally thought to take place at the shock fronts generated by interaction of the primary energy source with the surrounding medium, where the gamma-rays might also be produced. The lack of a significant change in the gamma-ray light curve when the optical emission develops suggests that the gamma-rays are not produced at the shock front, but closer to the site of the original explosion.Comment: 10 pages, 2 figures. Accepted for publication in Nature. For additional information see http://www.umich.edu/~rotse

Cytogenetics of bisexual/unisexual species of Poecilia. IV. Sex chromosomes, sex chromatin composition and Ag-NOR polymorphisms in Poecilia latipinna: a population from Mexico

Cytogenetic analysis using C-banding, silver staining and fluorescent staining was carried out on a population sample of Poecilia Iatipinna derived from Tampico, Mexico, to verify the presence of sex chromosomes in individuals from the southern areas of this species range and to investigate the extent of C-band and Ag-NOR polymorphisms. Females were found to have W heteromorphic chromosomes, with large amounts of heterochromatin-rich in AT nucleotide sequences. C-banding corresponded to the pattern proposed as typical for the genus. Specimens share one of the Ag- NOR locations previously described in populations from the U.S.A. and show additional ones as well

Cytogenetics of Bisexual/Unisexual Species of Poecilia. VI. Additional Nucleolus Organizer Region Chromosomal Clones of Poecilia Formosa (Amazon Molly) From Texas, With a Survey of Chromosomal Clones Detected in the Amazon Molly

This study reports the results of different staining techniques on the chromosomes of two Poecilia formosa lineages, providing evidence of two additional nucleolus organizer region (NOR) chromosomal clones in this gynogenetic fish. A comparative analysis of chromosomal clones detected in the Amazon molly, along with their frequency and distribution in different collecting sites, is also presented, and clonal heterogeneity resulting from chromosome changes is discussed

Focal adhesion kinase depletion reduces human hepatocellular carcinoma growth by repressing enhancer of zeste homolog 2

Hepatocellular carcinoma (HCC) is the most common type of liver cancer in humans. The focal adhesion tyrosine kinase (FAK) is often over-expressed in human HCC and FAK inhibition may reduce HCC cell invasiveness. However, the anti-oncogenic effect of FAK knockdown in HCC cells remains to be clarified. We found that FAK depletion in HCC cells reduced in vitro and in vivo tumorigenicity, by inducing G2/M arrest and apoptosis, decreasing anchorage-independent growth, and modulating the expression of several cancer-related genes. Among these genes, we showed that FAK silencing decreased transcription and nuclear localization of enhancer of zeste homolog 2 (EZH2) and its tri-methylation activity on lysine 27 of histone H3 (H3K27me3). Accordingly, FAK, EZH2 and H3K27me3 were concomitantly upregulated in human HCCs compared to non-tumor livers. In vitro experiments demonstrated that FAK affected EZH2 expression and function by modulating, at least in part, p53 and E2F2/3 transcriptional activity. Moreover, FAK silencing downregulated both EZH2 binding and histone H3K27me3 levels at the promoter of its target gene NOTCH2. Finally, we found that pharmacological inhibition of FAK activity resembled these effects although milder. In summary, we demonstrate that FAK depletion reduces HCC cell growth by affecting cancer-promoting genes including the pro-oncogene EZH2. Furthermore, we unveil a novel unprecedented FAK/EZH2 crosstalk in HCC cells, thus identifying a targetable network paving the way for new anticancer therapies