Arabidopsis cyclophilins direct plasmodesmata-targeting of mobile mRNA via organelle hitchhiking

Plants selectively transport mobile mRNAs through intercellular pores, plasmodesmata (PD), to distribute spatial information for synchronizing meristematic differentiation with environmental dynamics. However, how plants recognize and deliver mobile mRNAs to PD remains unknown. Here, by using RNA-live cell imaging, we show that mobile mRNAs hitchhike on organelle trafficking to transport to PD. Perturbed cytoskeleton organization or organelle trafficking severely disrupts the subcellular distribution of mobile mRNAs. We further show that Arabidopsis rotamase cyclophilins (ROCs), which are organelle-localized RNA-binding proteins (RBPs), specifically bind mobile mRNAs on the surface of organelles to direct PD-targeting. Arabidopsis roc quadruple mutants showed reduced in PD-targeting of mobile mRNAs, along with phenotype alterations. ROCs can move intercellularly and form RNA-protein complexes in phloem, suggesting the roles of ROCs in delivery of mobile mRNAs through PD. Our results highlight that an RBP-mediated hitchhiking system is purposely recruited to orient plant-mobile mRNAs to PD for intercellular transport.

Intercellular transport of RNA can limit heritable epigenetic changes

RNAs in circulation carry sequence-specific regulatory information between cells in animal, plant, and host-pathogen systems. Double-stranded RNA (dsRNA) delivered into the extracellular space of the nematode C. elegans accumulates within the germline and reaches progeny. Here we provide evidence for spatial, temporal, and substrate specificity in the transport of dsRNA from parental circulation to progeny. Temporary loss of dsRNA transport resulted in the persistent accumulation of mRNA from a germline gene. The expression of this gene varied among siblings and even between gonad arms within one animal. Perturbing RNA regulation of the gene created new epigenetic states that lasted for many generations. Thus, one role for the transport of dsRNA into the germline in every generation is to limit heritable changes in gene expression.One Sentence SummaryRNA from parental circulation reduces heritable changes in gene expression.

Exosomes and myocardial infarction: scientific and practical interest

A review of the literature on the biological role of exosomes in the pathophysiology of a number of pathological conditions, including damage to the heart muscle in the variant of myocardial infarction (MI), is presented. In the last decade, exosomes have begun to be actively studied; a lot of data have appeared on their nature and role in intercellular transport and signaling both in normal conditions and in pathology. Exosomes are important carriers of biological information, facilitating intercellular communication and participating in the pathophysiology of various cardiovascular diseases. In myocardial infarction, massive cardiomyocyte death triggers a strong inflammatory response, which is a vital process for cardiac damage, repair, and remodeling. A growing body of evidence suggests that exosomes are involved in the inflammatory response and immune regulation after MI.

Sequestration to lipid droplets promotes histone availability by preventing turnover of excess histones

Because both dearth and overabundance of histones result in cellular defects, histone synthesis and demand are typically tightly coupled. In Drosophila embryos, histones H2B/H2A/H2Av accumulate on lipid droplets (LDs), cytoplasmic fat storage organelles. Without LD-binding, maternally provided H2B/H2A/H2Av are absent, but how LDs ensure histone storage is unclear. Using quantitative imaging, we uncover when during oogenesis these histones accumulate, and which step of accumulation is LD-dependent. LDs originate in nurse cells (NCs) and are transported to the oocyte. Although H2Av accumulates on LDs in NCs, the majority of the final H2Av pool is synthesized in oocytes. LDs promote intercellular transport of the histone-anchor Jabba and thus its presence in the ooplasm. Ooplasmic Jabba then prevents H2Av degradation, safeguarding the H2Av stockpile. Our findings provide insight into the mechanism for establishing histone stores during Drosophila oogenesis and shed light on the function of LDs as protein-sequestration sites.

The careful control of Polo kinase by APC/C-Ube2C ensures the intercellular transport of germline centrosomes during Drosophila oogenesis

A feature of metazoan reproduction is the elimination of maternal centrosomes from the oocyte. In animals that form syncytial cysts during oogenesis, including Drosophila and human, all centrosomes within the cyst migrate to the oocyte where they are subsequently degenerated. The importance and the underlying mechanism of this event remain unclear. Here, we show that, during early Drosophila oogenesis, control of the Anaphase Promoting Complex/Cyclosome (APC/C), the ubiquitin ligase complex essential for cell cycle control, ensures proper transport of centrosomes into the oocyte through the regulation of Polo/Plk1 kinase, a critical regulator of the integrity and activity of the centrosome. We show that novel mutations in the APC/C-specific E2, Vihar/Ube2c, that affect its inhibitory regulation on APC/C cause precocious Polo degradation and impedes centrosome transport, through destabilization of centrosomes. The failure of centrosome migration correlates with weakened microtubule polarization in the cyst and allows ectopic microtubule nucleation in nurse cells, leading to the loss of oocyte identity. These results suggest a role for centrosome migration in oocyte fate maintenance through the concentration and confinement of microtubule nucleation activity into the oocyte. Considering the conserved roles of APC/C and Polo throughout the animal kingdom, our findings may be translated into other animals.

Quantitative analyses reveal extracellular dynamics of Wnt ligands in Xenopus embryos

The mechanism of intercellular transport of Wnt ligands is still a matter of debate. To better understand this issue, we examined the distribution and dynamics of Wnt8 in Xenopus embryos. While Venus-tagged Wnt8 was found on the surfaces of cells close to Wnt-producing cells, we also detected its dispersal over distances of 15 cell diameters. A combination of fluorescence correlation spectroscopy and quantitative imaging suggested that only a small proportion of Wnt8 ligands diffuses freely, whereas most Wnt8 molecules are bound to cell surfaces. Fluorescence decay after photoconversion showed that Wnt8 ligands bound on cell surfaces decrease exponentially, suggesting a dynamic exchange of bound forms of Wnt ligands. Mathematical modelling based on this exchange recapitulates a graded distribution of bound, but not free, Wnt ligands. Based on these results, we propose that Wnt distribution in tissues is controlled by a dynamic exchange of its abundant bound and rare free populations.

Metabolic differentiation and intercellular nurturing underpin bacterial endospore formation

Despite intensive research, the role of metabolism in bacterial sporulation remains poorly understood. Here, we demonstrate that Bacillus subtilis sporulation entails a marked metabolic differentiation of the two cells comprising the sporangium: the forespore, which becomes the dormant spore, and the mother cell, which dies as sporulation completes. Our data provide evidence that metabolic precursor biosynthesis becomes restricted to the mother cell and that the forespore becomes reliant on mother cell–derived metabolites for protein synthesis. We further show that arginine is trafficked between the two cells and that proposed proteinaceous channels mediate small-molecule intercellular transport. Thus, sporulation entails the profound metabolic reprogramming of the forespore, which is depleted of key metabolic enzymes and must import metabolites from the mother cell. Together, our results provide a bacterial example analogous to progeny nurturing.