Current findings on the molecular mechanisms underlying anhydrobiosis in Polypedilum vanderplanki

© 2016 Elsevier Inc.Water is an essential molecule for living organisms. However, some organisms can survive in environments which receive no rainfall for months and in which ordinary life cannot survive. How do they endure the extended dry season? The sleeping chironomid Polypedilum vanderplanki, which inhabits sub-Saharan Africa, exhibits extreme tolerance to complete desiccation, a process termed anhydrobiosis. During anhydrobiosis these organisms dry up and entirely shut down their metabolism. However, when the dried larvae are immersed in water, their metabolism is resumed. Interestingly, anhydrobiosis allows these organisms to tolerate not only desiccation but also high and low temperatures, the absence of oxygen, radiation, and chemical stresses. Here, we describe the mechanisms by which P. vanderplanki achieves anhydrobiosis revealed in our recent research

Regulation of Gene Expression for L-Isoaspartyl O-Methyltransferases by Cis-Elements Associated with “Heat-Shock Polytene Chromosome Puffing Formation” in the Anhydrobiotic Midge

© 2016, Springer Science+Business Media New York.L-isoaspartyl O-methyltransferases (PIMTs) are known mostly because of their protein chain reparation activity in plant seeds, but also in many other organisms, from bacteria to mammals, including human. The main function of PIMT is recognition and methylation of spontaneously isomerized aspartate residue (Asp) in the amino acid sequences of cellular proteins, and thus preventing their conformation shifts and subsequent inactivation or loss of particular functions. The correlation between PIMT activity and accumulation of isomerized aspartate residues is well studied and used as a marker of isoAsp presence, whereas regulation pathways of PIMT genes are not clear yet. In our study, we propose a possible model for multiple paralogous PIMT gene regulation in the genome of an anhydrobiotic insect Polypedilum vanderplanki. Analysis of promoter regions revealed that PIMT genes possess enriched motif nearby +1 site, associated with GO term heat-shock polytene chromosome puffing. Poly(ADP-ribose) polymerase (PARP) is involved in this process of chromatin loosening and subsequent transcription activation of related genes. This result implied that expression of PIMT genes in P. vanderplanki could be regulated by chromatin modification

The complete mitochondrial genome of an anhydrobiotic midge Polypedilum vanderplanki (Chironomidae, Diptera)

© 2015 Informa UK Limited, trading as Taylor & Francis Group.In this work, we describe a complete mitochondrial genome of chironomid Polypedilum vanderplanki. In spite of unique ecology of this species, the larvae are able to survive years of complete desiccation; the circular mitochondrial genome keeps basic structure and consists of 13 protein-coding genes, 2 rRNA, and 22 tRNA genes, and has a total length of 16 060 bp. Low GC level, small regulatory region, and unusually high number and length of non-coding spacers are the main determined features

In Vitro Recombinant Expression of Novel Protective Protein Highly Accumulated in Dry State in an Anhydrobiotic Insect

© 2016, Springer Science+Business Media New York.Recent intensive studies showed that ability of several groups of organisms to withstand complete desiccation (anhydrobiosis state) is largely based on the activity of several groups of key proteins, including representatives of intrinsically disordered ones. In the largest known anhydrobiotic animal, the sleeping chironomid, both proteomic and genome-wide/targeted mRNA expression analysis suggest that several groups of the novel proteins greatly contribute to the formation of the molecular shield. Among them, 114 aa-long protein, dryporin. Being one of the most abundant in the desiccated larvae on protein level and showing one of the highest expression on mRNA level, this protein shows lack of the obvious homology with other known proteins. In this study, we successfully produced recombinant dryporin protein using BY-2 cell free lysate and showed the evidence of post-translational modification of the protein in the anhydrobiotic larvae

Chironomid Midges (Diptera, Chironomidae) Show Extremely Small Genome Sizes

© 2015 Zoological Society of Japan. Chironomid midges (Diptera; Chironomidae) are found in various environments from the high Arctic to the Antarctic, including temperate and tropical regions. In many freshwater habitats, members of this family are among the most abundant invertebrates. In the present study, the genome sizes of 25 chironomid species were determined by flow cytometry and the resulting C-values ranged from 0.07 to 0.20 pg DNA (i.e. from about 68 to 195 Mbp). These genome sizes were uniformly very small and included, to our knowledge, the smallest genome sizes recorded to date among insects. Small proportion of transposable elements and short intron sizes were suggested to contribute to the reduction of genome sizes in chironomids. We discuss about the possible developmental and physiological advantages of having a small genome size and about putative implications for the ecological success of the family Chironomidae

LEA4 Protein Is Likely to Be Involved in Direct Protection of DNA Against External Damage

© 2016, Springer Science+Business Media New York.Anhydrobiotic larvae of an African chironomid Polypedilum vanderplanki are known to be highly resistant to various abiotic stress factors, including ultraviolet radiation. The comparison of survival rates after different doses of UV irradiation between P. vanderplanki larvae and closely related non-anhydrobiotic Polypedilum nubifer larvae showed strongly enhanced resistance of P. vanderplanki to UV irradiation, especially in completely desiccated state. Plasmid-based assay showed an evidence of contribution of LEA4 protein to the protection of the larvae’s DNA against UV damage

New Antioxidant Genes from an Anhydrobiotic Insect: Unique Structural Features in Functional Motifs of Thioredoxins

© 2016, Springer Science+Business Media New York.Polipedilum vanderplanki is the most complex known organism able to survive body desiccation via entering a state of suspended metabolism called anhydrobiosis. This unique ability is based on the specific molecular machinery involving a synthesis of non-reducing sugar trehalose and a variety of protective proteins. Genes encoding these protective proteins are extensively duplicated in the P. vanderplanki genome and become hugely upregulated in response to desiccation. Some of these highly expressed genes encode substitutions of amino acids crucial for the function of corresponding proteins. An intriguing group of protective proteins in P. vanderplanki are thioredoxins (TRX). These antioxidant proteins are important for P. vanderplanki anhydrobiosis since desiccation is tightly related to the elevated production of free radicals and oxidative damage. The TRX set is unprecedentedly expanded in the P. vanderplanki genome up to 25 TRX genes. Genomes of congeneric midge Polipedilum nubifer, Apis mellifera, Drosophila melanogaster, and Anopheles gambiae encode only 3–7 TRX genes. Moreover, all three P. vanderplanki thioredoxin genes most expressed at 24 h of P. vanderplanki larva desiccation encode for proteins missing the typical CxxC motif

Genetic background of enhanced radioresistance in an anhydrobiotic insect: transcriptional response to ionizing radiations and desiccation

© 2016, Springer Japan.It is assumed that resistance to ionizing radiation, as well as cross-resistance to other abiotic stresses, is a side effect of the evolutionary-based adaptation of anhydrobiotic animals to dehydration stress. Larvae of Polypedilum vanderplanki can withstand prolonged desiccation as well as high doses of ionizing radiation exposure. For a further understanding of the mechanisms of cross-tolerance to both types of stress exposure, we profiled genome-wide mRNA expression patterns using microarray techniques on the chironomid larvae collected at different stages of desiccation and after exposure to two types of ionizing radiation—70 Gy of high-linear energy transfer (LET) ions (4He) and the same dose of low-LET radiation (gamma rays). In expression profiles, a wide transcriptional response to desiccation stress that much exceeded the amount of up-regulated transcripts to irradiation exposure was observed. An extensive group of coincidently up-regulated overlapped transcripts in response to desiccation and ionizing radiation was found. Among this, overlapped set of transcripts was indicated anhydrobiosis-related genes: antioxidants, late embryogenesis abundant (LEA) proteins, and heat-shock proteins. The most overexpressed group was that of protein-L-isoaspartate/D-aspartate O-methyltransferase (PIMT), while probes, corresponding to LEA proteins, were the most represented. Performed functional analysis showed strongly enriched gene ontology terms associated with protein methylation. In addition, active processes of DNA repair were detected. We assume that the cross-tolerance of the sleeping chironomid to both desiccation and irradiation exposure comes from a complex mechanism of adaptation to anhydrobiosis

Karyotypical characteristics of two allopatric African populations of anhydrobiotic Polypedilum Kieffer, 1912 (Diptera, Chironomidae) originating from Nigeria and Malawi

© Ninel A. Petrova et al. The African chironomid Polypedilum vanderplanki Hinton, 1951 is the only chironomid able to withstand almost complete desiccation in an ametabolic state known as anhydrobiosis. The karyotypes of two allopatric populations of this anhydrobiotic chironomid, one from Nigeria and another from Malawi, were described according to the polytene giant chromosomes. The karyotype from the Nigerian population was presented as the reference chromosome map for P. vanderplanki. Both populations, Nigerian and Malawian, showed the same number of chromosomes (2n=8), but important differences were found in the band sequences of polytene chromosomes, and in the number and the arrangement of active regions between the two populations. Such important differences raise the possibility that the Malawian population could constitute a distinct new species of anhydrobiotic chironomid

Transcriptome analysis of the anhydrobiotic cell line Pv11 infers the mechanism of desiccation tolerance and recovery

© 2018, The Author(s). The larvae of the African midge, Polypedilum vanderplanki, can enter an ametabolic state called anhydrobiosis to overcome fatal desiccation stress. The Pv11 cell line, derived from P. vanderplanki embryo, shows desiccation tolerance when treated with trehalose before desiccation and resumes proliferation after rehydration. However, the molecular mechanisms of this desiccation tolerance remain unknown. Here, we performed high-throughput CAGE-seq of mRNA and a differentially expressed gene analysis in trehalose-treated, desiccated, and rehydrated Pv11 cells, followed by gene ontology analysis of the identified differentially expressed genes. We detected differentially expressed genes after trehalose treatment involved in various stress responses, detoxification of harmful chemicals, and regulation of oxidoreduction that were upregulated. In the desiccation phase, L-isoaspartyl methyltransferase and heat shock proteins were upregulated and ribosomal proteins were downregulated. Analysis of differentially expressed genes during rehydration supported the notion that homologous recombination, nucleotide excision repair, and non-homologous recombination were involved in the recovery process. This study provides initial insights into the molecular mechanisms underlying the extreme desiccation tolerance of Pv11 cells