Zhukova, M. | bioRxiv Science

bioRxiv2025

Stability of orb mRNA in Drosophila ovaries is regulated by cis-regulatory elements in the three prime untranslated region and influences germ cell specification

Orb is one of two Drosophila mRNA-binding CPEB proteins that activate or repress translation by mediating polyadenylation and deadenylation of target mRNAs through interaction with CPE motifs in their 3UTRs. Orb is one of the key regulators of oocyte specification and polarity. This regulation acts through establishment and maintenance of a 3UTR-dependent positive autoregulatory loop. In 16-cell cysts, positive autoregulation is necessary to accumulate high levels of orb mRNA and protein in one of the two pro-oocytes. A previous study showed that deletion of the orb 3UTR fragment containing CPE sites leads to a failure in proper orb mRNA and protein localization; as a result, oocytes are not specified in 16-cell cysts, and egg chambers contain only nurse cells. In the present study, we found that deletion of CPE and CPE-like motifs disrupts proper Orb protein localization and oocyte specification in germaria. CPE motifs are indispensable for orb mRNA stability: deletion of CPE and CPE-like sequences reduces orb mRNA stability to one third of level in wild type. When the 3UTR is deleted, the remaining 115-nucleotide sequence, which does not include CPE motifs, is sufficient for nurse cell development. Removal of this sequence leads to a further decrease in orb mRNA stability and a drop of Orb protein to undetectable levels. Oogenesis stops in region 2a/2b of the germarium, where the checkpoint is localized, and egg chambers do not form. We propose that CPE motifs are required for orb 3UTR-mediated Orb accumulation which drives oocyte specification, whereas low levels of unlocalized Orb protein expressed in the absence of Orb autoregulation are sufficient for nurse cell specification.

cell biology↗

bioRxiv2018

Gut microbial compositions mirror caste-specific diets in a major lineage of eusocial insects

Eusocial insects owe their ecological success to the division of labour and processes within colonies often rely on the presence of specific microbial symbionts, but associations between microbial community compositions and castes with different tasks and diets within colonies remain largely unexplored. Fungus-growing termites evolved to use fungi to externally degrade plant material, complemented by specific and complex gut microbiotas. Here we explore to which extent division of labour and dietary differences within fungus-growing termite castes are linked to gut bacterial community structure. Using amplicon sequencing, we characterise community compositions in sterile (worker and soldier) and reproductive (queen and king) termites and combine this with gut enzyme, microscopy, and in situ analyses to further elucidate sterile caste-specific microbiota compositions. Gut bacterial communities are structured primarily according to termite caste and genus. In contrast to the observed rich and diverse sterile caste microbiotas, royal pair microbiotas are extremely skewed and dominated by few bacterial taxa, reflecting the specialised dietary intake and unique, reproduction-centred lifestyle of the queen and king.

microbiology↗