Repression of Abd-B by Polycomb is critical for cell identity maintenance in adult Drosophila testis

CRISPR/Cas9-mediated knockout of the abdominal-B homeotic gene in the global pest, fall armyworm (Spodoptera frugiperda)

The Homeotic complex (Hox) genes play a crucial role in determining segment identity and appendage morphology in bilaterian animals along the antero-posterior axis. Recent studies have expanded to agricultural pests such as fall armyworm (FAW), scientifically known as Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae), which significantly threatens global agricultural productivity. However, the specific role of the hox gene Sfabd-B in FAW remains unexplored. This research investigates the spatial and temporal expression patterns of Sfabd-B in various tissues at different developmental stages using quantitative real-time polymerase chain reaction (qRT-PCR). Additionally, we explored the potential function of the Sfabd-B gene located in the FAW genome using CRISPR/Cas9 technology. The larval mutant phenotypes can be classified into three subgroups as compared with wild-type individuals, that is, an excess of pedis in the posterior abdomen, deficient pedis due to segmental fusion and deviations in the posterior abdominal segments. Importantly, significant differences in mutant phenotypes between male and female individuals were also evident during the pupal and adult phases. Notably, both the decapentaplegic (dpp) and cuticular protein 12 (cp 12) genes displayed a substantial marked decrease in expression levels in the copulatory organ of male mutants and the ovipositor of female mutants compared with the wild type. These findings highlight the importance of Sfabd-B in genital tract patterning, providing a potential target for improving genetic control.

Chromatin state transitions in the Drosophila intestinal lineage identify principles of cell-type specification

Tissue homeostasis relies on rewiring of stem cell transcriptional programs into those of differentiated cells. Here, we investigate changes in chromatin occurring in a bipotent adult stem cells. Combining mapping of chromatin-associated factors with statistical modeling, we identify genome-wide transitions during differentiation in the adult Drosophila intestinal stem cell (ISC) lineage. Active, stem-cell-enriched genes transition to a repressive heterochromatin protein-1-enriched state more prominently in enteroendocrine cells (EEs) than in enterocytes (ECs), in which the histone H1-enriched Black state is preeminent. In contrast, terminal differentiation genes associated with metabolic functions follow a common path from a repressive, primed, histone H1-enriched Black state in ISCs to active chromatin states in EE and EC cells. Furthermore, we find that lineage priming has an important function in adult ISCs, and we identify histone H1 as a mediator of this process. These data define underlying principles of chromatin changes during adult multipotent stem cell differentiation.

Interlocking of co-opted developmental gene networks in Drosophila and the evolution of pre-adaptive novelty

The re-use of genes in new organs forms the base of many evolutionary novelties. A well-characterised case is the recruitment of the posterior spiracle gene network to the Drosophila male genitalia. Here we find that this network has also been co-opted to the testis mesoderm where is required for sperm liberation, providing an example of sequentially repeated developmental co-options. Associated to this co-option event, an evolutionary expression novelty appeared, the activation of the posterior segment determinant Engrailed to the anterior A8 segment controlled by common testis and spiracle regulatory elements. Enhancer deletion shows that A8 anterior Engrailed activation is not required for spiracle development but only necessary in the testis. Our study presents an example of pre-adaptive developmental novelty: the activation of the Engrailed transcription factor in the anterior compartment of the A8 segment where, despite having no specific function, opens the possibility of this developmental factor acquiring one. We propose that recently co-opted networks become interlocked, so that any change to the network because of its function in one organ, will be mirrored by other organs even if it provides no selective advantage to them.

The complex role of transcription factor GAGA in germline death during Drosophila spermatogenesis: transcriptomic and bioinformatic analyses

The GAGA protein (also known as GAF) is a transcription factor encoded by the Trl gene in D. melanogaster. GAGA is involved in the regulation of transcription of many genes at all stages of fly development and life. Recently, we investigated the participation of GAGA in spermatogenesis and discovered that Trl mutants experience massive degradation of germline cells in the testes. Trl underexpression induces autophagic death of spermatocytes, thereby leading to reduced testis size. Here, we aimed to determine the role of the transcription factor GAGA in the regulation of ectopic germline cell death. We investigated how Trl underexpression affects gene expression in the testes. We identified 15,993 genes in three biological replicates of our RNA-seq analysis and compared transcript levels between hypomorphic Trl ^R85/Trl ³⁶² and Oregon testes. A total of 2,437 differentially expressed genes were found, including 1,686 upregulated and 751 downregulated genes. At the transcriptional level, we detected the development of cellular stress in the Trl-mutant testes: downregulation of the genes normally expressed in the testes (indicating slowed or abrogated spermatocyte differentiation) and increased expression of metabolic and proteolysis-related genes, including stress response long noncoding RNAs. Nonetheless, in the Flybase Gene Ontology lists of genes related to cell death, autophagy, or stress, there was no enrichment with GAGA-binding sites. Furthermore, we did not identify any specific GAGA-dependent cell death pathway that could regulate spermatocyte death. Thus, our data suggest that GAGA deficiency in male germline cells leads to an imbalance of metabolic processes, impaired mitochondrial function, and cell death due to cellular stress.

Effects of Three Types of Pollen on the Growth and Development of Honey Bee Larvae (Hymenoptera, Apidae)

Pollen serves as an essential protein source for honey bee larvae. The nutrients in pollen greatly influence larval growth and development. Here, the survival, prepupal weight, developmental stage, pollen digestibility and midgut cells in honey bee (Apis mellifera L.) larvae were evaluated by performing in vitro and 5-ethynyl-2′-deoxyuridine (EdU) assays on larvae reared on three single pollens (Brassica napus L., Armeniaca sibirica L., and Pyrus bretschneideri Rehd.) and a pollen mixture (mixture of the three pollens in equal proportions). The results showed that the survival rate of larvae fed 10 mg of rape pollen was lowest (P < 0.05), but there were no notable differences in the survival rate among the groups receiving the other types and doses of pollen (P > 0.05). The prepupal weight of larvae fed apricot pollen was significantly lower than those of the other groups (P < 0.05). The digestibility of rape pollen and the pollen mixture were dramatically higher than those of apricot and pear pollen (P < 0.05). Pear and mixed pollen exerted negative effects on the nuclear area of midgut cells in the early larval stage (P < 0.05). In conclusion, detection of larval midgut cells using the EdU assay might be an effective method to assess the pollen nutritive value in honey bees. Compared to apricot and pear pollen, rape pollen was more beneficial in larval honey bee growth and development.

Mitochondrial genotype alters the impact of rapamycin on the transcriptional response to nutrients in Drosophila

BACKGROUND

In addition to their well characterized role in cellular energy production, new evidence has revealed the involvement of mitochondria in diverse signaling pathways that regulate a broad array of cellular functions. The mitochondrial genome (mtDNA) encodes essential components of the oxidative phosphorylation (OXPHOS) pathway whose expression must be coordinated with the components transcribed from the nuclear genome. Mitochondrial dysfunction is associated with disorders including cancer and neurodegenerative diseases, yet the role of the complex interactions between the mitochondrial and nuclear genomes are poorly understood.

RESULTS

Using a Drosophila model in which alternative mtDNAs are present on a common nuclear background, we studied the effects of this altered mitonuclear communication on the transcriptomic response to altered nutrient status. Adult flies with the 'native' and 'disrupted' genotypes were re-fed following brief starvation, with or without exposure to rapamycin, the cognate inhibitor of the nutrient-sensing target of rapamycin (TOR). RNAseq showed that alternative mtDNA genotypes affect the temporal transcriptional response to nutrients in a rapamycin-dependent manner. Pathways most greatly affected were OXPHOS, protein metabolism and fatty acid metabolism. A distinct set of testis-specific genes was also differentially regulated in the experiment.

CONCLUSIONS

Many of the differentially expressed genes between alternative mitonuclear genotypes have no direct interaction with mtDNA gene products, suggesting that the mtDNA genotype contributes to retrograde signaling from mitochondria to the nucleus. The interaction of mitochondrial genotype (mtDNA) with rapamycin treatment identifies new links between mitochondria and the nutrient-sensing mTORC1 (mechanistic target of rapamycin complex 1) signaling pathway.

Epigenetic regulation of drosophila germline stem cell maintenance and differentiation

Gametogenesis is one of the most extreme cellular differentiation processes that takes place in Drosophila male and female germlines. This process begins at the germline stem cell, which undergoes asymmetric cell division (ACD) to produce a self-renewed daughter that preserves its stemness and a differentiating daughter cell that undergoes epigenetic and genomic changes to eventually produce haploid gametes. Research in molecular genetics and cellular biology are beginning to take advantage of the continually advancing genomic tools to understand: (1) how germ cells are able to maintain their identity throughout the adult reproductive lifetime, and (2) undergo differentiation in a balanced manner. In this review, we focus on the epigenetic mechanisms that address these two questions through their regulation of germline-soma communication to ensure germline stem cell identity and activity.

Maintenance of Cell Fate by the Polycomb Group Gene Sex Combs Extra Enables a Partial Epithelial Mesenchymal Transition in Drosophila

Epigenetic silencing by Polycomb group (PcG) complexes can promote epithelial-mesenchymal transition (EMT) and stemness and is associated with malignancy of solid cancers. Here we report a role for Drosophila PcG repression in a partial EMT event that occurs during wing disc eversion, an early event during metamorphosis. In a screen for genes required for eversion we identified the PcG genes Sex combs extra (Sce) and Sex combs midleg (Scm). Depletion of Sce or Scm resulted in internalized wings and thoracic clefts, and loss of Sce inhibited the EMT of the peripodial epithelium and basement membrane breakdown, ex vivo. Targeted DamID (TaDa) using Dam-Pol II showed that Sce knockdown caused a genomic transcriptional response consistent with a shift toward a more stable epithelial fate. Surprisingly only 17 genes were significantly upregulated in Sce-depleted cells, including Abd-B, abd-A, caudal, and nubbin. Each of these loci were enriched for Dam-Pc binding. Of the four genes, only Abd-B was robustly upregulated in cells lacking Sce expression. RNAi knockdown of all four genes could partly suppress the Sce RNAi eversion phenotype, though Abd-B had the strongest effect. Our results suggest that in the absence of continued PcG repression peripodial cells express genes such as Abd-B, which promote epithelial state and thereby disrupt eversion. Our results emphasize the important role that PcG suppression can play in maintaining cell states required for morphogenetic events throughout development and suggest that PcG repression of Hox genes may affect epithelial traits that could contribute to metastasis.

Hox genes limit germ cell formation in the short germ insect Gryllus bimaculatus

Hox genes are conserved transcription factor-encoding genes that specify the identity of body regions in bilaterally symmetrical animals. In the cricket Gryllus bimaculatus, a member of the hemimetabolous insect group Orthoptera, the induction of a subset of mesodermal cells to form the primordial germ cells (PGCs) is restricted to the second through the fourth abdominal segments (A2 to A4). In numerous insect species, the Hox genes Sex-combs reduced (Scr), Antennapedia (Antp), Ultrabithorax (Ubx), and abdominal-A (abd-A) jointly regulate the identities of middle and posterior body segments, suggesting that these genes may restrict PGC formation to specific abdominal segments in G. bimaculatus Here we show that reducing transcript levels of some or all of these Hox genes results in supernumerary and/or ectopic PGCs, either individually or in segment-specific combinations, suggesting that the role of these Hox genes is to limit PGC development with respect to their number, segmental location, or both. These data provide evidence of a role for this ancient group of genes in PGC development.

Architects meets Repairers: The interplay between homeobox genes and DNA repair

Homeobox genes are widely considered the major protagonists of embryonic development and tissue formation. For the past decades, it was established that the deregulation of these genes is intimately related to developmental abnormalities and a broad range of diseases in adults. Since the proper regulation and expression of homeobox genes are necessary for a successful developmental program and tissue function, their relation to DNA repair mechanisms become a necessary discussion. However, important as it is, studies focused on the interplay between homeobox genes and DNA repair are scarce, and there is no critical discussion on the subject. Hence, in this work, I aim to provide the first review of the current knowledge of the interplay between homeobox genes and DNA repair mechanisms, and offer future perspectives on this, yet, young ground for new researches. Critical discussion is conducted, together with a careful assessment of each reviewed topic.