Comparative transcriptional analysis uncovers molecular processes in early and mature somatic cyst cells of Drosophila testes

The tight interaction between somatic and germline cells is conserved in animal spermatogenesis. The testes of Drosophila melanogaster are the model of choice to identify processes responsible for mature gamete production. However, processes of differentiation and soma-germline interactions occurring in somatic cyst cells are currently understudied. Here we focused on the comparison of transcriptome expression patterns of early and mature somatic cyst cells to find out the developmental changes taking place in them. We employed a FACS-based approach for the isolation of early and mature somatic cyst cells from fly testes, subsequent preparation of RNA-Seq libraries, and analysis of gene differential expression in the sorted cells. We found increased expression of genes involved in cell cycle-related processes in early cyst cells, which is necessary for the proliferation and self-renewal of a crucial population of early cyst cells, cyst stem cells. Genes proposedly required for lamellipodium-like projection organization for proper cyst formation were also detected among the upregulated ones in early cyst cells. Gene Ontology and interactome analyses of upregulated genes in mature cyst cells revealed a striking over-representation of gene categories responsible for metabolic and catabolic cellular processes, as well as genes supporting the energetic state of the cells provided by oxidative phosphorylation that is carried out in mitochondria. Our comparative analyses of differentially expressed genes revealed major peculiarities in early and mature cyst cells and provide novel insight into their regulation, which is important for male fertility.

The 3'UTR of the Drosophila CPEB translation factor gene orb2 plays a crucial role in spermatogenesis

CPEB proteins are conserved translation regulators involved in multiple biological processes. One of these proteins in Drosophila, Orb2, is a principal player in spermatogenesis. It is required for meiosis and spermatid differentiation. During the later process, orb2 mRNA and protein are localized within the developing spermatid. To evaluate the role of the orb2 mRNA 3'UTR in spermatogenesis, we used the CRISPR/Cas9 system to generate a deletion of the orb2 3'UTR, orb2R. This deletion disrupts the process of spermatid differentiation but has no apparent effect on meiosis. Differentiation abnormalities include defects in the initial polarization of the 64-cell spermatid cysts, mislocalization of mRNAs and proteins in the elongating spermatid tails, altered morphology of the elongating spermatid tails, and defects in the assembly of the individualization complex. These disruptions in differentiation appear to arise because orb2 mRNA and protein are not properly localized within the 64-cell spermatid cyst.

The Drosophila RNA Helicase Belle (DDX3) Non-Autonomously Suppresses Germline Tumorigenesis Via Regulation of a Specific mRNA Set

DDX3 subfamily DEAD-box RNA helicases are essential developmental regulators of RNA metabolism in eukaryotes. belle, the single DDX3 ortholog in Drosophila, is required for fly viability, fertility, and germline stem cell maintenance. Belle is involved both in translational activation and repression of target mRNAs in different tissues; however, direct targets of Belle in the testes are essentially unknown. Here we showed that belle RNAi knockdown in testis cyst cells caused a disruption of adhesion between germ and cyst cells and generation of tumor-like clusters of stem-like germ cells. Ectopic expression of β-integrin in cyst cells rescued early stages of spermatogenesis in belle knockdown testes, indicating that integrin adhesion complexes are required for the interaction between somatic and germ cells in a cyst. To address Belle functions in spermatogenesis in detail we performed cross-linking immunoprecipitation and sequencing (CLIP-seq) analysis and identified multiple mRNAs that interacted with Belle in the testes. The set of Belle targets includes transcripts of proteins that are essential for preventing the tumor-like clusters of germ cells and for sustaining spermatogenesis. By our hypothesis, failures in the translation of a number of mRNA targets additively contribute to developmental defects observed in the testes with belle knockdowns both in cyst cells and in the germline.

An RNAi Screen for Genes Required for Growth of Drosophila Wing Tissue

Cell division and tissue growth must be coordinated with development. Defects in these processes are the basis for a number of diseases, including developmental malformations and cancer. We have conducted an unbiased RNAi screen for genes that are required for growth in the Drosophila wing, using GAL4-inducible short hairpin RNA (shRNA) fly strains made by the Drosophila RNAi Screening Center. shRNA expression down the center of the larval wing disc using dpp-GAL4, and the central region of the adult wing was then scored for tissue growth and wing hair morphology. Out of 4,753 shRNA crosses that survived to adulthood, 18 had impaired wing growth. FlyBase and the new Alliance of Genome Resources knowledgebases were used to determine the known or predicted functions of these genes and the association of their human orthologs with disease. The function of eight of the genes identified has not been previously defined in Drosophila The genes identified included those with known or predicted functions in cell cycle, chromosome segregation, morphogenesis, metabolism, steroid processing, transcription, and translation. All but one of the genes are similar to those in humans, and many are associated with disease. Knockdown of lin-52, a subunit of the Myb-MuvB transcription factor, or βNACtes6, a gene involved in protein folding and trafficking, resulted in a switch from cell proliferation to an endoreplication growth program through which wing tissue grew by an increase in cell size (hypertrophy). It is anticipated that further analysis of the genes that we have identified will reveal new mechanisms that regulate tissue growth during development.

BTF3 sustains cancer stem-like phenotype of prostate cancer via stabilization of BMI1

Background

Cancer stem-like traits contribute to prostate cancer (PCa) progression and metastasis. Deciphering the novel molecular mechanisms underlying stem-like traits may provide important insight for developing novel therapeutics.

Methods

Immunohistochemistry and immunofluorescence assays in prostatic tissues; gain- and loss-of-function analyses using ectopic overexpression and shRNAs in PCa cell lines; measurements of tumorigenic and stemness properties, and transcription in vitro and in vivo; transcriptional analysis in public databases.

Results

We identified that overexpression of BTF3 in PCa tissues and BTF3 expression highly correlates to stem-like traits. Cancer stem-like characteristics in PCa including self-renewal and metastatic potential were impaired by BTF3 loss and promoted by BTF3 overexpression. Mechanistically, BTF3 could stabilize BMI1, which is a crucial regulator of prostate stem cell self-renewal. More importantly, our data revealed that BTF3 is highly predictive of poor prognosis and may help in risk stratification of PCa patients.

Conclusions

BTF3 promotes PCa progression though modeling stem-like traits in PCa. BTF3 represents a stratification marker in PCa progression and outcomes.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1222-z) contains supplementary material, which is available to authorized users.