Dosage compensation

About: Dosage compensation is a research topic. Over the lifetime, 1920 publications have been published within this topic receiving 124589 citations.

Escaping the evolutionary trap? Sex chromosome turnover in basilisks and related lizards (Corytophanidae: Squamata)

Abstract: Most pleurodont lizard families (anoles, iguanas and their relatives), with the exception of the basilisks and casquehead lizards (family Corytophanidae), share homologous XX/XY sex chromosomes, syntenic with chicken chromosome 15. Here, we used a suite of methods (i.e. RADseq, RNAseq and qPCR) to identify corytophanid sex chromosomes for the first time. We reveal that all examined corytophanid species have partially degenerated XX/XY sex chromosomes, syntenic with chicken chromosome 17. Transcriptomic analyses showed that the expression of X-linked genes in the corytophanid, Basiliscus vittatus, is not balanced between the sexes, which is rather exceptional under male heterogamety, and unlike the dosage-balanced sex chromosomes in other well-studied XX/XY systems, including the green anole, Anolis carolinensis. Corytophanid sex chromosomes may represent a rare example of a turnover away from stable, differentiated sex chromosomes. However, because of poor phylogenetic resolution among pleurodont families, we cannot reject the alternative hypothesis that corytophanid sex chromosomes evolved independently from an unknown ancestral system.

Microarray analysis of the Df1 mouse model of the 22q11 deletion syndrome.

Abstract: The 22q11 deletion syndrome (22q11DS; DiGeorge/velo-cardio-facial syndrome) primarily affects the structures comprising the pharyngeal arches and pouches resulting in arch artery, cardiac, parathyroid, thymus, palatal and craniofacial defects. Tbx1 haploinsufficiency is thought to account for the main structural anomalies observed in the 22q11DS. The Df1 deleted mouse provides a model for 22q11DS, the deletion reflecting Tbx1 haploinsufficiency in the context of the deletion of 21 adjacent genes. We examined the expression of genes in Df1 embryos at embryonic day (E) 10.5, a stage when the arch-artery phenotype is fully penetrant. Our aims were threefold, with our primary aim to identify differentially regulated genes. Second, we asked whether any of the genes hemizygous in Df1 were dosage compensated to wild type levels, and third we investigated whether genes immediately adjacent to the deletion were dysregulated secondary to a position effect. Utilisation of oligonulceotide arrays allowed us to achieve our aims with 9 out of 12 Df1 deleted genes passing the stringent statistical filtering applied. Several genes involved in vasculogenesis and cardiogenesis were validated by real time quantitative PCR (RTQPCR), including Connexin 45, a gene required for normal vascular development, and Dnajb9 a gene implicated in microvascular differentiation. There was no evidence of any dosage compensation of deleted genes, suggesting this phenomenon is rare, and no dysregulation of genes mapping immediately adjacent to the deletion was detected. However Crkl, another gene implicated in the 22q11DS phenotype, was found to be downregulated by microarray and RTQPCR.

Evidence for dosage compensation in parthenogenetic Hymenoptera.

Abstract: Amount of DNA-Feulgen staining in individual somatic nuclei and mature sperm of the parthenogenetic wasps, Habrobracon juglandis, H. serinopae, and Mormoniella vitripennis, were determined with a scanning microdensitometer. The haploid genome for both species of Habrobracon was estimated to be 0.15–0.16×10−12 g DNA, corresponding to a molecular weight of roughly 10×1010 daltons. The haploid genome of M. vitripennis is approximately twice this value, 0.33–0.34×10−12 g, or about 20×1010 daltons. Measurements made on dividing nuclei from syncytial preblastoderm embryos of H. juglandis and M. vitripennis showed that the chromosomes of impaternate males were present in the haploid number and contained the C amount of DNA; whereas nuclei from female preblastoderm embryos contained the diploid number of chromosomes and the 2C amount of DNA. However, hemocyte and brain cell nuclei from either male or female adult wasps contained 2C and 4C amounts of DNA. Both sexes also showed equivalent levels of polyploidy (8C, 16C, or 32C) in Malpighian tubule nuclei. Therefore, in these parthenogenetic species, a mechanism must exist that compensates during later development for the initial two-fold difference in the chromatin content of somatic nuclei in haploid male and diploid female embryos. Hemocytes from impaternate Mormoniella diploid males and triploid females contain the 2C and 3C amounts of DNA, respectively. Therefore dosage compensation involves an additional cycle of DNA replication only in haploid cells, and it insures that a certain minimum quantity of DNA is received by each somatic cell.

Spatial dynamics of evolving dosage compensation in a young sex chromosome system

Abstract: The loss of Y-linked genes during sex chromosome evolution creates a potentially deleterious low gene dosage in males. Recent studies have reported different strategies of dosage compensation. Unfortunately, most of these studies investigated taxa with comparatively old sex chromosome systems, which may limit insights into the evolution of dosage compensation and thus into the causes of different compensation strategies. Using deep RNA sequencing, we investigate differential expression patterns along the young XY chromosomes of threespine sticklebacks. Our strata-specific analyses provide new insights into the spatial patterns during the early stages of the evolution of dosage compensation. In particular, our results indicate systematic upregulation of male gene expression in stratum II, which in turn causes female hypertranscription in the same stratum. These findings are consistent with theoretical predictions that selection during early stages of sex chromosome evolution is stronger for a compensating upregulation in males than for the countercompensation of female hyperexpression. In contrast, no elevated gene expression is detectable in stratum I. We argue that strata-specific differences in compensating male gene expression may evolve in response to differences in the prevailing mechanism of Y chromosome degeneration.

Molecular genetic aspects of sex determination in Drosophila melanogaster.

Abstract: The molecular analyses of three of the regulatory genes (transformer (tra), doublesex (dsx), and transformer-2 (tra-2)) controlling sexual differentiation in Drosophila have demonstrated that the control of RNA processing has a major role in regulating somatic sexual differentiation. The activities of both the tra and dsx genes are controlled at the level of RNA processing. In the case of tra the use of different splice acceptor sites results in a functional transcript being produced only in females, whereas at dsx the use of different splice acceptor sites in the two sexes results in the production of transcripts that encode different proteins in males and females. The tra-2 gene has been shown to be necessary for the processing of the dsx pre-mRNA in females and the conceptual translation of a tra-2 cDNA shows that it encodes a protein with similarity to a family of RNA-binding proteins which includes known splicesome components. We previously suggested that the pattern of sexual differentiation and dosage compensation characteristic of a male was a default regulatory state. The findings reviewed here provide a molecular basis for this default expression in males as well as an insight into how females differ from males in control of the expression of these genes. For both the tra and dsx genes the molecular basis of their male (default) state of expression appears to be the processing of their transcripts by the housekeeping RNA splicing machinery.(ABSTRACT TRUNCATED AT 250 WORDS)