Mosquito ribosomal protein S3 lacks a critical glutamine residue associated with DNA repair activity in homologous Drosophila proteins

From Mosquito Ovaries to Ecdysone; from Ecdysone to Wolbachia: One Woman's Career in Insect Biology

In anautogenous mosquitoes, synchronous development of terminal ovarian follicles after a blood meal provides an important model for studies on insect reproduction. Removal and implantation of ovaries, in vitro culture of dissected tissues and immunological assays for vitellogenin synthesis by the fat body showed that the Aedes aegypti (L.) (Diptera, Culicidae) mosquito ovary produces a factor essential for egg production. The discovery that the ovarian factor was the insect steroid hormone, ecdysone, provided a model for co-option of the larval hormones as reproductive hormones in adult insects. In later work on cultured mosquito cells, ecdysone was shown to arrest the cell cycle, resulting in an accumulation of diploid cells in G1, prior to initiation of DNA synthesis. Some mosquito species, such as Culex pipiens L. (Diptera, Culicidae), harbor the obligate intracellular bacterium, Wolbachia pipientis Hertig (Rickettsiales, Anaplasmataceae), in their reproductive tissues. When maintained in mosquito cell lines, Wolbachia abundance increases in ecdysone-arrested cells. This observation facilitated the recovery of high levels of Wolbachia from cultured cells for microinjection and genetic manipulation. In female Culex pipiens, it will be of interest to explore how hormonal cues that support initiation and progression of the vitellogenic cycle influence Wolbachia replication and transmission to subsequent generations via infected eggs.

Knockdown of RpL36 in testes impairs spermatogenesis in Drosophila melanogaster

Many ribosomal proteins (RPs) not only play essential roles in ribosome biogenesis, but also have "extraribosomal" functions in various cellular processes. RpL36 encodes ribosomal protein L36, a component of the 60S subunit of ribosomes in Drosophila melanogaster. We report here that RpL36 is required for spermatogenesis in D. melanogaster. After showing the evolutionary conservation of RpL36 sequences in animals, we revealed that the RpL36 expression level in fly testes was significantly higher than in ovaries. Knockdown RpL36 in fly testes resulted in a significantly decreased egg hatch rate when these males mated with wild-type females. Furthermore, 76.67% of the RpL36 knockdown fly testes were much smaller in comparison to controls. Immunofluorescence staining exhibited that in the RpL36 knockdown testis hub cell cluster was enlarged, while the number of germ cells, including germ stem cells, was reduced. Knockdown of RpL36 in fly testis caused much fewer or no mature sperms in seminal vesicles. The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) signal was stronger in RpL36 knockdown fly testes than in the control testes, but the TUNEL-positive cells could not be stained by Vasa antibody, indicating that apoptotic cells are not germ cells. The percentage of pH3-positive cells among the Vasa-positive cells was significantly reduced. The expression of genes involved in cell death, cell cycle progression, and JAK/STAT signaling pathway was significantly changed by RpL36 knockdown in fly testes. These results suggest that RpL36 plays an important role in spermatogenesis, likely through JAK/STAT pathway, thus resulting in defects in cell-cycle progression and cell death in D. melanogaster testes.

Wolbachia in mosquitoes from the Central Valley of California, USA

BACKGROUND

Wolbachia bacteria are widely distributed throughout terrestrial arthropod species. These bacteria can manipulate reproduction and influence the vector competence of their hosts. Recently, Wolbachia have been integrated into vector control programmes for mosquito management. A number of supergroups and strains exist for Wolbachia, and they have yet to be characterized for many mosquito species. In this study, we examined Wolbachia prevalence and their phylogenetic relationship to other Wolbachia, using mosquitoes collected in Merced County in the Central Valley of California.

METHODS

Adult mosquitoes were collected from 85 sites in Merced County, California in 2017 and 2018. Traditional and quantitative PCR were used to investigate the presence or absence and the density of Wolbachia, using Wolbachia-specific 16S rRNA and Wolbachia-surface protein (wsp) genes. The supergroup of Wolbachia was determined, and Multilocus Sequence Typing (MLST) by sequencing five housekeeping genes (coxA, gatB, ftsZ, hcpA and fbpA) was also used to determine Wolbachia supergroup as well as strain.

RESULTS

Over 7100 mosquitoes of 12 species were collected: Aedes melanimon, Ae. nigromaculis, Ae. vexans, Ae. aegypti, Culex pipiens, Cx. stigmatosoma, Cx. tarsalis, Anopheles franciscanus, An. freeborni, An. punctipennis, Culiseta incidens and Cs. inornata. Eight showed evidence of Wolbachia. To our knowledge, this study is the first to report detection of Wolbachia in five of these species (Ae. melanimon, Cx. stigmatosoma, Cx. tarsalis, Cs. incidens and Cs. inornata). Culex pipiens and Cx. stigmatosoma had a high frequency and density of Wolbachia infection, which grouped into supergroup B; Cs. inornata clustered with supergroup A. MLST comparisons identified Cx. pipiens and Cx. stigmatosoma as wPip strain type 9 supergroup B. Six species had moderate to low (< 14%) frequencies of Wolbachia. Four species were negative, Ae. nigromaculis, An. franciscanus, An. freeborni and Ae. aegypti.

CONCLUSIONS

New records of Wolbachia detection were found in mosquitoes from Merced County, California. Culex stigmatosoma and Cs. inornata were new records for Wolbachia supergroup B and A, respectively. Other species with Wolbachia occurred with low frequency and low density. Detection of Wolbachia in mosquitoes can be used to inform potential vector control applications. Future study of Wolbachia within Cx. stigmatosoma and Cs. inornata in California and through the range of these species could further explore Wolbachia infection in these two species.

Evolution of proteasome regulators in eukaryotes

All living organisms require protein degradation to terminate biological processes and remove damaged proteins. One such machine is the 20S proteasome, a specialized barrel-shaped and compartmentalized multicatalytic protease. The activity of the 20S proteasome generally requires the binding of regulators/proteasome activators (PAs), which control the entrance of substrates. These include the PA700 (19S complex), which assembles with the 20S and forms the 26S proteasome and allows the efficient degradation of proteins usually labeled by ubiquitin tags, PA200 and PA28, which are involved in proteolysis through ubiquitin-independent mechanisms and PI31, which was initially identified as a 20S inhibitor in vitro. Unlike 20S proteasome, shown to be present in all Eukaryotes and Archaea, the evolutionary history of PAs remained fragmentary. Here, we made a comprehensive survey and phylogenetic analyses of the four types of regulators in 17 clades covering most of the eukaryotic supergroups. We found remarkable conservation of each PA700 subunit in all eukaryotes, indicating that the current complex PA700 structure was already set up in the last eukaryotic common ancestor (LECA). Also present in LECA, PA200, PA28, and PI31 showed a more contrasted evolutionary picture, because many lineages have subsequently lost one or two of them. The paramount conservation of PA700 composition in all eukaryotes and the dynamic evolution of PA200, PA28, and PI31 are discussed in the light of current knowledge on their physiological roles.

Evaluation of Reference Genes for RT-qPCR in Tribolium castaneum (Coleoptera: Tenebrionidae) Under UVB Stress

Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) has become a widely used technique to quantify gene expression. It is necessary to select appropriate reference genes for normalization. In the present study, we assessed the expression stability of seven candidate genes in Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) irradiated by ultraviolet B (UVB) at different developmental stages for various irradiation time periods. The algorithms of geNorm, NormFinder, and BestKeeper were applied to determine the stability of these candidate genes. Ribosomal protein genes RpS3, RpL13A, and β-actin gene (ActB) showed the highest stability across all UVB irradiation time points, whereas expression of other normally used reference genes, such as those encoding the β-tubulin gene TUBB and the E-cadherin gene CAD, varied at different developmental stages. This study will potentially provide more suitable reference gene candidates for RT-qPCR analysis in T. castaneum subjected to environmental stresses, particularly UV irradiation.