Multivalent interactions with RNA drive recruitment and dynamics in biomolecular condensates in Xenopus oocytes.

RNA localization and biomolecular condensate formation are key biological strategies for organizing the cytoplasm and generating cellular polarity. In Xenopus oocytes, RNAs required for germ layer patterning localize in biomolecular condensates, termed Localization bodies (L-bodies). Here, we have used an L-body RNA-binding protein, PTBP3, to test the role of RNA-protein interactions in regulating the biophysical characteristics of L-bodies in vivo and PTBP3-RNA condensates in vitro. Our results reveal that RNA-protein interactions drive recruitment of PTBP3 and localized RNA to L-bodies and that multivalent interactions tune the dynamics of the PTBP3 after localization. In a concentration-dependent manner, RNA becomes non-dynamic and interactions with the RNA determine PTBP3 dynamics within these biomolecular condensates in vivo and in vitro. Importantly, RNA, and not protein, is required for maintenance of the PTBP3-RNA condensates in vitro, pointing to a model where RNA serves as a non-dynamic substructure in these condensates.

L-bodies are RNA-protein condensates driving RNA localization in Xenopus oocytes.

Ribonucleoprotein (RNP) granules are membraneless compartments within cells, formed by phase separation, that function as regulatory hubs for diverse biological processes. However, the mechanisms by which RNAs and proteins interact to promote RNP granule structure and function in vivo remain unclear. In Xenopus laevis oocytes, maternal mRNAs are localized as large RNPs to the vegetal hemisphere of the developing oocyte, where local translation is critical for proper embryonic patterning. Here we demonstrate that RNPs containing vegetally localized RNAs represent a new class of cytoplasmic RNP granule, termed localization-bodies (L-bodies). We show that L-bodies contain a dynamic protein-containing phase surrounding a nondynamic RNA-containing phase. Our results support a role for RNA as a critical component within these RNP granules and suggest that cis-elements within localized mRNAs may drive subcellular RNA localization through control over phase behavior.

Rab-E and its interaction with myosin XI are essential for polarised cell growth.

The fundamental process of polarised exocytosis requires the interconnected activity of molecular motors trafficking vesicular cargo within a dynamic cytoskeletal network. In plants, few mechanistic details are known about how molecular motors, such as myosin XI, associate with their secretory cargo to support the ubiquitous processes of polarised growth and cell division. Live-cell imaging coupled with targeted gene knockouts and a high-throughput RNAi assay enabled the first characterisation of the loss of Rab-E function. Yeast two-hybrid and subsequent in silico structural prediction uncovered a specific interaction between Rab-E and myosin XI that is conserved between P. patens and A. thaliana. Rab-E co-localises with myosin XI at sites of active exocytosis, and at the growing tip both proteins are spatiotemporally coupled. Rab-E is required for normal plant growth in P. patens and the rab-E and myosin XI phenotypes are rescued by A. thaliana's Rab-E1c and myosin XI-K/E, respectively. Both PpMyoXI and AtMyoXI-K interact with PpRabE14, and the interaction is specifically mediated by PpMyoXI residue V1422. This interaction is required for polarised growth. Our results suggest that the interaction of Rab-E and myosin XI is a conserved feature of polarised growth in plants.

Organizing the oocyte: RNA localization meets phase separation.

RNA localization is a key biological strategy for organizing the cytoplasm and generating both cellular and developmental polarity. During RNA localization, RNAs are targeted asymmetrically to specific subcellular destinations, resulting in spatially and temporally restricted gene expression through local protein synthesis. First discovered in oocytes and embryos, RNA localization is now recognized as a significant regulatory strategy for diverse RNAs, both coding and non-coding, in a wide range of cell types. Yet, the highly polarized cytoplasm of the oocyte remains a leading model to understand not only the principles and mechanisms underlying RNA localization, but also links to the formation of biomolecular condensates through phase separation. Here, we discuss both RNA localization and biomolecular condensates in oocytes with a particular focus on the oocyte of the frog, Xenopus laevis.

Pertuzumab-associated diarrhea in HER2/neu-positive breast cancer patients: A comparison of trials to actual practice.

BACKGROUND: Although landmark trials in the metastatic (CLEOPATRA) and neo-adjuvant (NeoSphere; TRYPHAENA) settings identified all-grade diarrhea as a pertuzumab-associated adverse event, it was not classified as dose-limiting. In actual practice, diarrhea is often a reason for treatment modifications. OBJECTIVES: To compare the risk of pertuzumab-associated diarrhea in actual practice to the risks in randomized controlled trials. METHODS: We conducted a retrospective cohort study of HER2/neu-positive breast cancer patients who received a pertuzumab-containing regimen between January 2012 and August 2015. We calculated the risk of diarrhea with 95% confidence limits (CLs), and then used two-sample t-tests to compare the risk between trials and actual practice. RESULTS: A total of 27 patients in the study cohort received a pertuzumab-containing treatment regimen for HER2/neu-positive breast cancer. The overall risk of all-grade and severe diarrhea in actual practice was 70% (95% CLs 55-90%) and 37% (95% CLs 20-66%), respectively. No severe diarrhea was observed in the metastatic setting, and the risk of all-grade diarrhea (44%, 95% CLs 21-92%) was similar to the CLEOPATRA study (67%). The risk of all-grade diarrhea in the neo-adjuvant setting was 83% (95% CLs 68-100%), compared to 46% in the NeoSphere trial (p = 0.03). The risk of severe diarrhea (Grade 3-4) in the neo-adjuvant setting was 47% (95% CLs 27-80%) versus 6% in the NeoSphere (p < 0.0001) and 12% in the TRYPHAENA (p < 0.01) trials. CONCLUSIONS: The risk of all-grade and severe diarrhea associated with neoadjuvant pertuzumab use for HER2/neu-positive breast cancer was greater in actual practice than in trials.

Overuse and underuse of pegfilgrastim for primary prophylaxis of febrile neutropenia.

INTRODUCTION: Guidelines recommend pegfilgrastim for primary prophylaxis of febrile neutropenia after highly myelosuppressive chemotherapy. While deviations from guidelines could result in overuse and increased costs, underuse is also a concern and could compromise quality of care. Our objectives were to evaluate guideline adherence and quantify the extent to which physician heterogeneity may influence pegfilgrastim use. METHODS: We randomly sampled 550 patients from a retrospective cohort of those who received infusions at an academic cancer center between 1 September 2013 and 1 September 2014. Electronic medical and drug dispensing records provided information on patient characteristics, chemotherapy characteristics, prescribing physician, and pegfilgrastim administration. RESULTS: We included 154 patients treated by 25 physicians. About half of patients were male and mean age was 61.3 years. Forty (26.1%) patients had no febrile neutropenia risk factors, 62 (40.5%) had one, and 51 (33.3%) had two or more. Thirty patients (19.5%) received pegfilgrastim, of which 12 (40%) received palliative chemotherapy. Nine (60%) of 15 patients on a regimen with a febrile neutropenia risk ≥ 20% received pegfilgrastim. Pegfilgrastim use significantly varied by cancer type (p < 0.01), chemotherapy regimen (p < 0.001), and regimen febrile neutropenia risk (p < 0.001). Multivariable analysis reaffirmed the association between chemotherapy regimen febrile neutropenia risk ≥ 20% and pegfilgrastim use (odds ratio (OR) = 10.1, 95% confidence interval (CI): 1.6-62.7) and suggested that 31% (95% CI: 8%-71%) of the variation in use was attributable to physician characteristics. CONCLUSION: Pegfilgrastim was potentially overused for palliative chemotherapy and underused for chemotherapy regimens with febrile neutropenia risk ≥ 20%. Successful interventions to modify prescribing practices likely require an understanding of the relationship between specific physician characteristics and pegfilgrastim use.