Showing papers on "X hyperactivation published in 2015"
TL;DR: It appears that the Lucilia dosage compensation system is specific for genes endogenous to the X chromosome and cannot be co-opted by recently arrived transgenes.
Abstract: In most animals that have X and Y sex chromosomes, chromosome-wide mechanisms are used to balance X-linked gene expression in males and females. In the fly Drosophila melanogaster, the dosage compensation mechanism also generally extends to X-linked transgenes. Over 70 transgenic lines of the Australian sheep blowfly Lucilia cuprina have been made as part of an effort to develop male-only strains for a genetic control program of this major pest of sheep. All lines carry a constitutively expressed fluorescent protein marker gene. In all 12 X-linked lines, female larvae show brighter fluorescence than male larvae, suggesting the marker gene is not dosage compensated. This has been confirmed by quantitative RT-PCR for selected lines. To determine if endogenous X-linked genes are dosage compensated, we isolated 8 genes that are orthologs of genes that are on the fourth chromosome in D. melanogaster. Recent evidence suggests that the D. melanogaster fourth chromosome, or Muller element F, is the ancestral X chromosome in Diptera that has reverted to an autosome in Drosophila species. We show by quantitative PCR of male and female DNA that 6 of the 8 linkage group F genes reside on the X chromosome in L. cuprina. The other two Muller element F genes were found to be autosomal in L. cuprina, whereas two Muller element B genes were found on the same region of the X chromosome as the L. cuprina orthologs of the D. melanogaster Ephrin and gawky genes. We find that the L. cuprina X chromosome genes are equally expressed in males and females (i.e., fully dosage compensated). Thus, unlike in Drosophila, it appears that the Lucilia dosage compensation system is specific for genes endogenous to the X chromosome and cannot be co-opted by recently arrived transgenes.
22 citations
TL;DR: This paper measured the X-chromosome response to gene dosage in adult heads by RNA sequencing and observed modest and indistinguishable dosage compensation for both X chromosome and autosome genes, suggesting that the X chromosome is neither inherently more robust nor sensitive to dosage change.
Abstract: X chromosome dosage compensation is required for male viability in Drosophila. Dosage compensation relative to autosomes is two-fold, but this is likely to be due to a combination of homeostatic gene-by-gene regulation and chromosome-wide regulation. We have baseline values for gene-by-gene dosage compensation on autosomes, but not for the X chromosome. Given the evolutionary history of sex chromosomes, these baseline values could differ. We used a series of deficiencies on the X and autosomes, along with mutations in the sex-determination gene transformer-2, to carefully measure the sex-independent X-chromosome response to gene dosage in adult heads by RNA sequencing. We observed modest and indistinguishable dosage compensation for both X chromosome and autosome genes, suggesting that the X chromosome is neither inherently more robust nor sensitive to dosage change.
19 citations
TL;DR: The laboratory found that siRNA from an X-linked satellite repeat promotes X recognition by a yet unknown mechanism, which suggests that the large and mysterious fraction of the genome called “junk” DNA is actually instrumental in the evolution of sex chromosomes.
Abstract: Dimorphic sex chromosomes create problems. Males of many species, including Drosophila, are heterogametic, with dissimilar X and Y chromosomes. The essential process of dosage compensation modulates the expression of X-linked genes in one sex to maintain a constant ratio of X to autosomal expression. This involves the regulation of hundreds of dissimilar genes whose only shared property is chromosomal address. Drosophila males dosage compensate by up regulating X-linked genes 2 fold. This is achieved by the Male Specific Lethal (MSL) complex, which is recruited to genes on the X chromosome and modifies chromatin to increase expression. How the MSL complex is restricted to X-linked genes remains unknown. Recent studies of sex chromosome evolution have identified a central role for 2 types of repetitive elements in X recognition. Helitrons carrying sites that recruit the MSL complex have expanded across the X chromosome in at least one Drosophila species.1 Our laboratory found that siRNA from an X-linked sa...
6 citations
TL;DR: Results suggest that, rather than conflict driving mt-N genes off of the mammalian X, random biases on chromosomes that formed the X chromosome could explain the paucity of mt- N genes in the therian lineage.
Abstract: Two taxa studied to date, the therian mammals and Caenorhabditis elegans, display underrepresentations of mitonuclear genes (mt-N genes, nuclear genes whose products are imported to and act within the mitochondria) on their X chromosomes. This pattern has been interpreted as the result of sexual conflict driving mt-N genes off of the X chromosome. However, studies in several other species have failed to detect a convergent biased distribution of sex-linked mt-N genes, leading to questions over the generality of the role of sexual conflict in shaping the distribution of mt-N genes. Here we tested whether mt-N genes moved off of the therian X chromosome following sex chromosome formation, consistent with the role of sexual conflict, or whether the paucity of mt-N genes on the therian X is a chance result of an underrepresentation on the ancestral regions that formed the X chromosome. We used a synteny-based approach to identify the ancestral regions in the platypus and chicken genomes that later formed the therian X chromosome. We then quantified the movement of mt-N genes on and off of the X chromosome and the distribution of mt-N genes on the human X and ancestral X regions. We failed to find an excess of mt-N gene movement off of the X. The bias of mt-N genes on ancestral therian X chromosomes was also not significantly different from the biases on the human X. Together our results suggest that, rather than conflict driving mt-N genes off of the mammalian X, random biases on chromosomes that formed the X chromosome could explain the paucity of mt-N genes in the therian lineage.
4 citations
TL;DR: This paper estimated fine-scale recombination rates across the 2.1-Mb garnet-scalloped region of the Drosophila melanogaster X chromosome by pooling male progeny inheriting crossovers within the region in groups of 100 for DNA sequencing.
Abstract: A paper published in this Journal ([Singh et al. 2013][1]) estimated fine-scale recombination rates across the 2.1-Mb garnet-scalloped ( g-sd ) region of the Drosophila melanogaster X chromosome by pooling male progeny inheriting crossovers within the region in groups of 100 for DNA sequencing. In
3 citations
TL;DR: The present study may suggest a novel karyotype associated with KS, a derivative X chromosome formed by translocation involving an X chromosome and a chromosome 18 in a Klinefelter syndrome patient with a 47,XXY karyotypes that has not yet been reported in the literature.
Abstract: A derivative X chromosome formed by translocation involving an X chromosome and a chromosome 18 in a Klinefelter syndrome (KS) patient with a 47,XXY karyotype has not been reported before. In this study, we present the clinical and molecular cytogenetic characteristics. The patient presented with small testes and azoospermia. G-banding analysis identified the karyotype as 47,XY,del(X)(p?11.4). Array CGH detected a 10.36-Mb duplication of chromosome region 18p11.22p11.32 (14,316-10,377,516) and a 111.18-Mb duplication of chromosome region Xp11.4q28 (61,931, 689-155,111,583), in addition to the normal chromosome 18 and an X chromosome. FISH results further revealed the extra 18p located at the end of the short arm of a deleted X chromosome, forming a derivative X chromosome. Finally, we identified the karyotype of the patient as 47,XY,+der(X)t(X;18)(p11.4;p11.22). The derivative X chromosome was maternally inherited. To our knowledge, this rare karyotype has not yet been reported in the literature. The present study may suggest a novel karyotype associated with KS.
3 citations