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.
Highlights
Very different mechanisms are used in the fly Drosophila melanogaster, the nematode Caenorhabditis elegans and in mammals to achieve X chromosome dosage compensation [1,2,3]
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
To investigate if linkage group F genes are X-linked in L. cuprina, we identified orthologs of Drosophila fourth chromosome genes in transcriptomes from the closely related blowfly, Lucilia sericata [25]
Summary
Very different mechanisms are used in the fly Drosophila melanogaster, the nematode Caenorhabditis elegans and in mammals to achieve X chromosome dosage compensation [1,2,3]. The MSL complex binds to active genes and upregulates expression, thereby achieving dosage compensation [6, 7]. The MSL complex is thought to initially bind to 150– 300 high affinity or chromatin entry sites on the X chromosome and spread to actively transcribed genes [4]. Most genes on the X chromosome do not need to bind the MSL complex with high affinity in order to be compensated. Consistent with this model is the finding that, in general, X-linked transgenes are dosage compensated [8,9,10]. At X chromosome locations both the cg3702 and Rpl genes were bound by the MSL complex in males and dosage compensated
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
