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High-resolution transcriptional profiling of Anopheles gambiae spermatogenesis reveals mechanisms of sex chromosome regulation.

ABSTRACT: Although of high priority for the development of genetic tools to control malaria-transmitting mosquitoes, only a few germline-specific regulatory regions have been characterised to date and the presence of global regulatory mechanisms, such as dosage compensation and meiotic sex chromosome inactivation (MSCI), are mostly assumed from transcriptomic analyses of reproductive tissues or whole gonads. In such studies, samples include a significant portion of somatic tissues inevitably complicating the reconstruction of a defined transcriptional map of gametogenesis. By exploiting recent advances in transgenic technologies and gene editing tools, combined with fluorescence-activated cell sorting and RNA sequencing, we have separated four distinct cell lineages from the Anopheles gambiae male gonads: premeiotic, meiotic (primary and secondary spermatocytes) and postmeiotic. By comparing the overall expression levels of X-linked and autosomal genes across the four populations, we revealed a striking transcriptional repression of the X chromosome coincident with the meiotic phase, classifiable as MSCI, and highlighted genes that may evade silencing. In addition, chromosome-wide median expression ratios of the premeiotic population confirmed the absence of dosage compensation in the male germline. Applying differential expression analysis, we highlighted genes and transcript isoforms enriched at specific timepoints and reconstructed the expression dynamics of the main biological processes regulating the key stages of sperm development and maturation. We generated the first transcriptomic atlas of A. gambiae spermatogenesis that will expand the available toolbox for the genetic engineering of vector control technologies. We also describe an innovative and multidimensional approach to isolate specific cell lineages that can be used for the targeted analysis of other A. gambiae organs or transferred to other medically relevant species and model organisms.

SUBMITTER: Taxiarchi C

PROVIDER: S-EPMC6795909 | biostudies-other | 2019 Oct

REPOSITORIES: biostudies-other

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High-resolution transcriptional profiling of Anopheles gambiae spermatogenesis reveals mechanisms of sex chromosome regulation.

Taxiarchi Chrysanthi C Kranjc Nace N Kriezis Antonios A Kyrou Kyros K Bernardini Federica F Russell Steven S Nolan Tony T Crisanti Andrea A Galizi Roberto R

Scientific reports 20191016 1

Although of high priority for the development of genetic tools to control malaria-transmitting mosquitoes, only a few germline-specific regulatory regions have been characterised to date and the presence of global regulatory mechanisms, such as dosage compensation and meiotic sex chromosome inactivation (MSCI), are mostly assumed from transcriptomic analyses of reproductive tissues or whole gonads. In such studies, samples include a significant portion of somatic tissues inevitably complicating ...[more]

PMID: 31619757

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Project description:BACKGROUNDChemosensory signal transduction guides the behavior of many insects, including Anopheles gambiae, the major vector for human malaria in sub-Saharan Africa. To better understand the molecular basis of mosquito chemosensation we have used whole transcriptome RNA sequencing (RNA-seq) to compare transcript expression profiles between the two major chemosensory tissues, the antennae and maxillary palps, of adult female and male An. gambiae.RESULTSWe compared chemosensory tissue transcriptomes to whole body transcriptomes of each sex to identify chemosensory enhanced genes. In the six data sets analyzed, we detected expression of nearly all known chemosensory genes and found them to be highly enriched in both olfactory tissues of males and females. While the maxillary palps of both sexes demonstrated strict chemosensory gene expression overlap, we observed acute differences in sensory specialization between male and female antennae. The relatively high expression levels of chemosensory genes in the female antennae reveal its role as an organ predominately assigned to chemosensation. Remarkably, the expression of these genes was highly conserved in the male antennae, but at much lower relative levels. Alternatively, consistent with a role in mating, the male antennae displayed significant enhancement of genes involved in audition, while the female enhancement of these genes was observed, but to a lesser degree.CONCLUSIONSThese findings suggest that the chemoreceptive spectrum, as defined by gene expression profiles, is largely similar in female and male An. gambiae. However, assuming sensory receptor expression levels are correlated with sensitivity in each case, we posit that male and female antennae are perceptive to the same stimuli, but possess inverse receptive prioritizations and sensitivities. Here we have demonstrated the use of RNA-seq to characterize the sensory specializations of an important disease vector and grounded future studies investigating chemosensory processes.

Project description:In many species, males and females display differences in their physiology that are not limited to the gonads. Sex differences in adult insects can comprise body size and feeding behaviour, as only female, but not male mosquitoes are blood-feeding in order to produce eggs. This is relevant since the malaria-causing parasite Plasmodium is transmitted by a female mosquito through a previous blood meal from an infected individual. The initiation of sex-specific developmental programs can be often linked to heteromorphic sex chromosomes (XX/XY in Anopheles). In males, the X-linked genes are only present in a single copy. To counteract this hemizygosity, Anopheles, like other species, exhibits dosage compensation (DC). Anopheles DC manifests by upregulation of the single male X ensuring the equal expression of sex-chromosomal genes between males and females. To date, the sex-specific differences at the transcriptome level related to the X/Y chromosomes and DC have been characterized at post-embryonic stages. Their onset during embryogenesis, especially during the early stages where the embryo switches from the maternal to the zygotic transcriptome, is largely uncharacterized to date. Here, we generate a sex-specific transcriptome atlas across Anopheles embryogenesis ending at the first larval stage. Along with the transition from the maternal to the zygotic transcriptome, many transcripts switch isoform, where the 3’ untranslated regions (UTR) of zygotic transcripts are significantly extended compared to their maternal counterpart. We also identify stage- and sex-specific splicing events. Comparing male and female embryos, we identify 120 sexually dimorphic protein coding genes and non-coding RNAs, indicating that sexually dimorphic gene expression is not widespread during embryogenesis. Furthermore, the imbalance of X-linked genes between males and females after zygotic genome activation is corrected shortly after, where the majority of genes exhibit DC around 9 hours of embryogenesis with further fine-tuning later in development. Our atlas provides a framework to explore sex differences in development and evolution and thereby, enables future functional analyses of sex-specific expression patterns and isoform usage.

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High-resolution transcriptional profiling of Anopheles gambiae spermatogenesis reveals mechanisms of sex chromosome regulation.

Publications

High-resolution transcriptional profiling of Anopheles gambiae spermatogenesis reveals mechanisms of sex chromosome regulation.

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