Functional characterization of insect-specific RabX6 of Bombyx mori

Small GTPase Rab40C is upregulated by 20-hydroxyecdysone and insulin pathways to regulate ovarian development and fecundity

The insulin and 20-hydroxyecdysone (20E) pathways coordinately regulate insect vitellogenesis and ovarian development. However, the detailed molecular mechanisms such as the genes mediating the cooperation of the interaction of these 2 pathways in regulating insect reproductive development are not well understood. In the present study, a small GTPase, Rab40C, was identified from the notorious agricultural pest Bactrocera dorsalis. In addition to the well-known RAB domain, it also has a unique SOCS-box domain, which is different from other Rab-GTPases. Moreover, we found that Rab40C was enriched in the ovaries of sexually mature females. RNA interference (RNAi)-mediated knockdown of BdRab40C resulted in a decrease in vitellogenin synthesis, underdeveloped ovaries, and low fertility. Furthermore, depletion of insulin receptor InR or the heterodimer receptor of 20E (EcR or USP) by RNAi significantly decreased the transcription of BdRab40C and resulted in lower fecundity. Further studies revealed that the transcription of BdRab40C could be upregulated by the injection of insulin or 20E. These results indicate that Rab40C participates in the insulin and 20E pathways to coordinately regulate reproduction in B. dorsalis. Our results not only provide new insights into the insulin- and 20E-stimulated regulatory pathways controlling female reproduction in insects but also contribute to the development of potential eco-friendly strategies for pest control.

The Acetylation Modification of SP1 Regulates the Protein Stability in Silkworm

Acetylation is a highly conservative and reversible post-translational modification. Acetylation modification can regulate gene expression by altering protein function and is widely identified in an increasing number of species. Previously, the acetylated proteome of silkworm was identified by combining acetylated polypeptide enrichment with nano-HPLC/MS/MS; the identification revealed that the SP proteins (SPs) were high acetylated. In this study, the acetylation of SP1, one of the SPs, was further confirmed using immunoprecipitation (IP) and Western blotting. Then, we found the acetylation could upregulate SP1 protein expression by enhancing the protein stability. Further research found that the acetylation of SP1 protein can competitively inhibit its ubiquitination and thus improve the stability and cell accumulation of SP1 protein by inhibiting the ubiquitin-mediated proteasome degradation pathway. This result provides a basis for acetylation to regulate the nutrient storage and utilization of silkworm.

The evolutionary landscape of the Rab family in chordates

Intracellular traffic amongst organelles represents a key feature for eukaryotes and is orchestrated principally by members of Rab family, the largest within Ras superfamily. Given that variations in Rab repertoire have been fundamental in animal diversification, we provided the most exhaustive survey regarding the Rab toolkit of chordates. Our findings reveal the existence of 42 metazoan conserved subfamilies exhibiting a univocal intron/exon structure preserved from cnidarians to vertebrates. Since the current view does not capture the Rab complexity, we propose a new Rab family classification in three distinct monophyletic clades. The Rab complement of chordates shows a dramatic diversification due to genome duplications and independent gene duplications and losses with sharp differences amongst cephalochordates, tunicates and gnathostome vertebrates. Strikingly, the analysis of the domain architecture of this family highlighted the existence of chimeric calcium-binding Rabs, which are animal novelties characterized by a complex evolutionary history in gnathostomes and whose role in cellular metabolism is obscure. This work provides novel insights in the knowledge of Rab family: our hypothesis is that chordates represent a hotspot of Rab variability, with many events of gene gains and losses impacting intracellular traffic capabilities. Our results help to elucidate the role of Rab members in the transport amongst endomembranes and shed light on intracellular traffic routes in vertebrates. Then, since the predominant role of Rabs in the molecular communication between different cellular districts, this study paves to way to comprehend inherited or acquired human disorders provoked by dysfunctions in Rab genes.