Wulsch, S. | bioRxiv Science

bioRxiv2023

A female heterogametic ZW sex-determination system in Acariformes

Sexual reproduction, while often associated with separate sexes, is an ancient and widespread feature of multicellular eukaryotes. While a diversity of sex-determination mechanisms exist, for many organisms, which of these mechanisms is used remains unknown. Exploring sex-determination mechanisms in Acariformes, among the oldest chelicerate clades, is intriguing due to its potential to unveil conserved sex-determination systems. This insight can have implications for understanding sex chromosome evolution and its broader impact on higher taxa.To identify the mechanism of sex determination in Acari, i.e., oribatid mites, we generated a high-quality chromosome-level genome assembly of Hermannia gibba (Koch, 1839) by combining PacBio HiFi and Hi-C sequencing. Coverage and allele-frequency analyses on pools of male and female individuals suggest a female-heterogametic ZW sex-determination system with little degeneration of the W chromosome. To date, this represents the only documented case of a ZW system in Acariformes. Further comparative studies in H. gibba will reveal how old the ZW system is and whether it exhibits conservation or polymorphism.

genomics↗

bioRxiv2019

5’ tRNA halves are highly expressed in the primate hippocampus and sequence-specifically regulate gene expression

Fragments of mature tRNAs have long been considered as mere degradation products without physiological function. However, recent reports show that tRNA fragments (tRFs) play prominent roles in diverse cellular processes across a wide spectrum of species. Contrasting the situation in other small RNA pathways the mechanisms behind these effects appear more diverse, more complex and are generally less well understood. In addition, surprisingly little is known about the expression profiles of tRFs across different tissues and species. Here, we provide an initial overview of tRF expression in different species and tissues, revealing very high tRF-levels particularly in the primate hippocampus. We further modulated the regulation capacity of selected tRFs in human cells by transfecting synthetic tRF mimics (\"overexpression\") or antisense-RNAs (\"inhibition\") and identified differentially expressed transcripts based on RNAseq. We then used a novel k-mer mapping approach to dissect the underlying targeting rules, demonstrating that 5 tRNA halves (5 tRHs) silence genes in a sequence-specific manner, while the most efficient target sites align to the mid-region of the 5 tRH and are located within the CDS or 3 UTR of the target. This amends previous observations that tRFs guide Argonaut proteins to silence their targets via a miRNA-like 5 seed match and suggests a yet unknown mechanism of regulation. Finally, our data suggests that some 5 tRHs are also able to sequence-specifically stabilize mRNAs as upregulated mRNAs are also significantly enriched for 5 tRH target sites.

molecular biology↗