Background: Retrotransposons with long terminal repeats (LTR retrotransposons) are widespread in all groups of eukaryotes and are often both the cause of new mutations and the source of new sequences. Apart from their high activity in generative and differentiation-stage tissues, LTR retrotransposons also become more active in response to different stressors. The precise causes of LTR retrotransposons’ activation in response to stress, however, have not yet been thoroughly investigated. Methods: We used RT-PCR to investigate the transcriptional profile of LTR retrotransposons and piRNA clusters in response to oxidative and chronic heat stresses. We used Oxford Nanopore sequencing to investigate the genomic environment of new insertions of the retrotransposons. We used bioinformatics methods to find the stress-induced transcription factor binding sites in LTR retrotransposons. Results: We studied the transposition activity and transcription level of LTR retrotransposons in response to oxidative and chronic heat stress and assessed the contribution of various factors that can affect the increase in their expression under stress conditions: the state of the piRNA-interference system, the influence of the genomic environment on individual copies, and the presence of the stress-induced transcription factor binding sites in retrotransposon sequences. Conclusions: The main reason for the activation of LTR retrotransposons under stress conditions is the presence of transcription factor binding sites in their regulatory sequences, which are triggered in response to stress and are necessary for tissue regeneration processes. Stress-induced transposable element activation can function as a trigger mechanism, triggering multiple signal pathways and resulting in a polyvariant cell response.

The most important sources of new components of genomes are transposable elements, which can occupy more than half of the nucleotide sequence of the genome in higher eukaryotes. Among the mobile components of a genome, a special place is occupied by retroelements, which are similar to retroviruses in terms of their mechanisms of integration into a host genome. The process of positive selection of certain sequences of transposable elements and retroviruses in a host genome is commonly called molecular domestication. There are many examples of evolutionary adaptations of gag (retroviral capsid) sequences as new regulatory sequences of different genes in mammals, where domesticated gag genes take part in placenta functioning and embryogenesis, regulation of apoptosis, hematopoiesis, and metabolism. The only gag-related gene has been found in the Drosophila genome—Gagr. According to the large-scale transcriptomic and proteomic analysis data, the Gagr gene in D. melanogaster is a component of the protein complex involved in the stress response. In this work, we consider the evolutionary processes that led to the formation of a new function of the domesticated gag gene and its adaptation to participation in the stress response. We discuss the possible functional role of the Gagr as part of the complex with its partners in Drosophila, and the pathway of evolution of proteins of the complex in eukaryotes to determine the benefit of the domesticated retroelement gag gene.

Phototaxis, positive (movement toward the light source) or negative (from the light source) mediates the adaptation of cyanobacteria to varying wave lengths and illumination intensity. The...

(1) Background: The Gagr gene in Drosophila melanogaster’s genome originated from the molecular domestication of retrotransposons and retroviruses’ gag gene. In all Drosophila species, the Gagr protein homologs exhibit a conserved structure, indicative of a vital role. Previous studies have suggested a potential link between the Gagr gene function and stress responses. (2) Methods: We compared flies with Gagr gene knockdown in all tissues to control flies in physiological tests and RNA-sequencing experiments. (3) Results: Flies with the Gagr gene knockdown exhibited shorter lifespans compared to control flies. Transcriptome analysis revealed that Gagr knockdown flies showed elevated transcription levels of immune response genes. We used ammonium persulfate, a potent stress inducer, to elicit a stress response. In control flies, ammonium persulfate activated the Toll, JAK/STAT, and JNK/MAPK signaling pathways. In contrast, flies with the Gagr gene knockdown displayed reduced expression of stress response genes. Gene ontology enrichment analysis identified categories of genes upregulated under ammonium persulfate stress in control flies but not in Gagr knockdown flies. These genes are involved in developmental control, morphogenesis, and central nervous system function. (4) Conclusion: Our findings indicate the significance of the Gagr gene in maintaining immune response and homeostasis.

In vertebrates, vitamin K is a cofactor for the gamma-glutamyl carboxylase (GGCX) involved in the carboxylation of glutamic acid residues. During the vitamin K cycle, vitamin K is oxidised by GGCX, and then reduced by vitamin K epoxide reductase (VKOR), which is inhibited by the synthetic coumarin warfarin. GGCX and VKOR are present in Drosophila melanogaster, but the existence of a vitamin K cycle remains unproven. Semi-lethal concentrations (LC₅₀) of K₃, menadione sodium bisulfite (MSB), and warfarin to neutralise the negative effect of MSB were selected for the Drosophila cultivation medium. LC-MS analysis was used for vitamin K measurement in flies’ extracts. The EPR method and RT-PCR were used for ROS level measurement and gene transcription assessment, respectively. The LC₅₀ of MSB in the medium resulted in a more than 20-fold increase in endogenous K₂ in flies, demonstrating the mechanism of K₃-to-K₂ conversion. Administration of 1 mM warfarin in the medium with MSB completely neutralised its negative effect on viability. Developed flies had decreased K₂ level, confirming the existence of a vitamin K cycle, and both reduced ROS level and hsp22 gene transcription. The biochemical pathways affected by elevated K₂ concentrations involves both elements of the vitamin K cycle and the adaptive mitochondrial antioxidant system.

Retrotransposons of the gypsy group of Drosophila melanogasterthat are structurally similar to retroviruses of vertebrates occupy an important place among retroelements of eukaryotes. The infectious...