Achilles, a New Family of Transcriptionally Active Retrotransposons from the Olive Fruit Fly, with Y Chromosome Preferential Distribution

Identification and functional verification of Y-chromosome-specific gene typo-gyf in Bactrocera dorsalis

Genes on the Y chromosome play important roles in male sex determination and development. The identification of Y-chromosome-specific genes not only provides a theoretical basis for the study of male reproductive development, but also offers genetic control targets for agricultural pests. However, Y-chromosome genes are rarely characterized due to their high repeatability and high heterochromatinization, especially in the oriental fruit fly. In this study, 1 011 Y-chromosome-specific candidate sequences were screened from 2 to 4 h Bactrocera dorsalis embryo datasets with the chromosome quotient method, 6 of which were identified as Y-chromosome-specific sequences by polymerase chain reaction, including typo-gyf, a 19 126-bp DNA sequence containing a 575-amino acid open reading frame. Testicular deformation and a significant reduction in sperm number were observed after typo-gyf knockdown with RNA interference in embryos. After typo-gyf knockout with clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9 in the embryonic stage, the sex ratio of the emergent adults was unbalanced, with far more females than males. A genotype analysis of these females with the Y-chromosome gene MoY revealed no sex reversal. Typo-gyf knockout led to the death of XY individuals in the embryonic stage. We conclude that typo-gyf is an essential gene for male survival, and is also involved in testicular development and spermatogenesis. The identification of typo-gyf and its functional verification provide insight into the roles of Y-chromosome genes in male development.

Transposable elements in the transcriptome of the velvetbean caterpillar Anticarsia gemmatalis Hübner, 1818 (Lepidoptera: Erebidae)

Transposable elements (TEs) are DNA sequences that possess the ability to move from one genomic location to another. These sequences contribute to a significant fraction of the genomes of most eukaryotes and can impact their architecture and regulation. In this paper, we present the first data related to the identification and characterization of TEs present in the transcriptome of Anticarsia gemmatalis. Approximately, 835 transcripts showed significant similarity to TEs and (or) characteristic domains. Retrotransposons accounted for 71.2% (595 sequences) of the identified elements, while DNA transposons were less abundant, with 240 annotations (28.8%). TEs were classified into 30 superfamilies, with SINE3/5S and Gypsy being the most abundant. Based on the sequences of TEs found in the transcriptome, we were able to locate conserved regions in the chromosomes of this species. The analysis of differential expression of TEs in susceptible and resistant strains, challenged and not challenged with Bacillus thuringiensis ( Bt) from in silico analysis, indicated that exposure to Bt can regulate the transcription of mobile genetic elements in the velvetbean caterpillar. Thus, these data contribute significantly to the knowledge of the structure and composition of these elements in the genome of this species, and suggest the role of stress on their expression.

Microbiomes of Blood-Feeding Arthropods: Genes Coding for Essential Nutrients and Relation to Vector Fitness and Pathogenic Infections. A Review

BACKGROUND

Blood-feeding arthropods support a diverse array of symbiotic microbes, some of which facilitate host growth and development whereas others are detrimental to vector-borne pathogens. We found a common core constituency among the microbiota of 16 different arthropod blood-sucking disease vectors, including Bacillaceae, Rickettsiaceae, Anaplasmataceae, Sphingomonadaceae, Enterobacteriaceae, Pseudomonadaceae, Moraxellaceae and Staphylococcaceae. By comparing 21 genomes of common bacterial symbionts in blood-feeding vectors versus non-blooding insects, we found that certain enteric bacteria benefit their hosts by upregulating numerous genes coding for essential nutrients. Bacteria of blood-sucking vectors expressed significantly more genes (p < 0.001) coding for these essential nutrients than those of non-blooding insects. Moreover, compared to endosymbionts, the genomes of enteric bacteria also contained significantly more genes (p < 0.001) that code for the synthesis of essential amino acids and proteins that detoxify reactive oxygen species. In contrast, microbes in non-blood-feeding insects expressed few gene families coding for these nutrient categories. We also discuss specific midgut bacteria essential for the normal development of pathogens (e.g., Leishmania) versus others that were detrimental (e.g., bacterial toxins in mosquitoes lethal to Plasmodium spp.).

Transcribed sex-specific markers on the Y chromosome of the oriental fruit fly, Bactrocera dorsalis

BACKGROUND

The Oriental fruit fly, Bactrocera dorsalis, is a highly polyphagous invasive species with a high reproductive potential. In many tropical and subtropical parts of the world it ranks as one of the major pests of fruits and vegetables. Due to its economic importance, genetic, cytogenetic, genomic and biotechnological approaches have been applied to understand its biology and to implement the Sterile Insect Technique, currently a part of area-wide control programmes against this fly. Its chromosome complement includes five pairs of autosomes and the sex chromosomes. The X and Y sex chromosomes are heteromorphic and the highly heterochromatic and degenerate Y harbours the male factor BdMoY. The characterization of the Y chromosome in this fly apart from elucidating its role as primary sex determination system, it is also of crucial importance to understand its role in male biology. The repetitive nature of the Y chromosome makes it challenging to sequence and characterise.

RESULTS

Using Representational Difference Analysis, fluorescent in situ hybridisation on mitotic chromosomes and in silico genome resources, we show that the B. dorsalis Y chromosome harbours transcribed sequences of gyf, (typo-gyf) a homologue of the Drosophila melanogaster Gigyf gene, and of a non-LTR retrotransposon R1. Similar sequences are also transcribed on the X chromosome. Paralogues of the Gigyf gene are also present on the Y and X chromosomes of the related species B. tryoni. Another identified Y-specific repetitive sequence linked to BdMoY appears to be specific to B. dorsalis.

CONCLUSIONS

Our random scan of the Y chromosome provides a broad picture of its general composition and represents a starting point for further applicative and evolutionary studies. The identified repetitive sequences can provide a useful Y-marking system for molecular karyotyping of single embryos. Having a robust diagnostic marker associated with BdMoY will facilitate studies on how BdMoY regulates the male sex determination cascade during the embryonic sex-determination window. The Y chromosome, despite its high degeneracy and heterochromatic nature, harbours transcribed sequences of typo-gyf that may maintain their important function in post-transcriptional mRNA regulation. That transcribed paralogous copies of Gigyf are present also on the X and that this genomic distribution is maintained also in B. tryoni raises questions on the evolution of sex chromosomes in Bactrocera and other tephritids.

Identification of Y-chromosome scaffolds of the Queensland fruit fly reveals a duplicated gyf gene paralogue common to many Bactrocera pest species

Bactrocera tryoni (Queensland fruit fly) are polyphagous horticultural pests of eastern Australia. Heterogametic males contain a sex-determining Y-chromosome thought to be gene poor and repetitive. Here, we report 39 Y-chromosome scaffolds (~700 kb) from B. tryoni identified using genotype-by-sequencing data and whole-genome resequencing. Male diagnostic PCR assays validated eight Y-scaffolds, and one (Btry4096) contained a novel gene with five exons that encode a predicted 575 amino acid protein. The Y-gene, referred to as typo-gyf, is a truncated Y-chromosome paralogue of X-chromosome gene gyf (1773 aa). The Y-chromosome contained ~41 copies of typo-gyf, and expression occurred in male flies and embryos. Analysis of 13 tephritid transcriptomes confirmed typo-gyf expression in six additional Bactrocera species, including Bactrocera latifrons, Bactrocera dorsalis and Bactrocera zonata. Molecular dating estimated typo-gyf evolved within the past 8.02 million years (95% highest posterior density 10.56-5.52 million years), after the split with Bactrocera oleae. Phylogenetic analysis also highlighted complex evolutionary histories among several Bactrocera species, as discordant nuclear (116 genes) and mitochondrial (13 genes) topologies were observed. B. tryoni Y-sequences may provide useful sites for future transgene insertions, and typo-gyf could act as a Y-chromosome diagnostic marker for many Bactrocera species, although its function is unknown.

Cytogenetic Analysis of the South American Fruit Fly Anastrepha fraterculus (Diptera:Tephritidae) Species Complex: Construction of Detailed Photographic Polytene Chromosome Maps of the Argentinian Af. sp.1 Member

Genetic and cytogenetic studies constitute a significant basis for understanding the biology of insect pests and the design and the construction of genetic tools for biological control strategies. Anastrepha fraterculus is an important pest of the Tephritidae family. It is distributed from southern Texas through eastern Mexico, Central America and South America causing significant crop damage and economic losses. Currently it is considered as a species complex; until now seven members have been described based on multidisciplinary approaches. Here we report the cytogenetic analysis of an Argentinian population characterized as Af. sp.1 member of the Anastrepha fraterculus species complex. The mitotic karyotype and the first detailed photographic maps of the salivary gland polytene chromosomes are presented. The mitotic metaphase complement consists of six (6) pairs of chromosomes, including one pair of heteromorphic sex chromosomes, with the male being the heterogametic sex. The analysis of the salivary gland polytene complement shows a total number of five long chromosomes that correspond to the five autosomes of the mitotic karyotype and a heterochromatic network corresponding to the sex chromosomes. Comparison of the polytene chromosome maps between this species and Anastrepha ludens shows significant similarity. The polytene maps presented here are suitable for cytogenetic studies that could shed light on the species limits within this species complex and support the development of genetic tools for sterile insect technique (SIT) applications.