Small GTPases and cilia

Small GTPases are key molecular switches that bind and hydrolyze GTP in diverse membrane-and cytoskeletonrelated cellular processes.Recently,mounting evidences have highlighted the role of various small GTPases,including the members in Arf/Arl,Rab,and Ran subfamilies,in cilia formation and function.Once overlooked as an evolutionary vestige,the primary cilium has attracted more and more attention in last decade because of its role in sensing various extracellular signals and the association between cilia dysfunction and a wide spectrum of human diseases,now called ciliopathies.Here we review recent advances about the function of small GTPases in the context of cilia,and the correlation between the functional impairment of small GTPases and ciliopathies.Understanding of these cellular processes is of fundamental importance for broadening our view of cilia development and function in normal and pathological states and for providing valuable insights into the role of various small GTPases in disease processes,and their potential as therapeutic targets.

Fine-tuning cell organelle dynamics during mitosis by small GTPases

During mitosis,the allocation of genetic material concurs with organelle transformation and distribution.The coordination of genetic material inheritance with organelle dynamics directs accurate mitotic progression,cell fate determination,and organismal homeostasis.Small GTPases belonging to the Ras superfamily regulate various cell organelles during division.Being the key regulators of membrane dynamics,the dysregulation of small GTPases is widely associated with cell organelle disruption in neoplastic and non-neoplastic diseases,such as cancer and Alzheimer’s disease.Recent discoveries shed light on the molecular properties of small GTPases as sophisticated modulators of a remarkably complex and perfect adaptors for rapid structure reformation.This review collects current knowledge on small GTPases in the regulation of cell organelles during mitosis and highlights the mediator role of small GTPase in transducing cell cycle signaling to organelle dynamics during mitosis.

Phenotype analysis and rescue on female FVB.129-Fmr1 knockout mice

Fragile X syndrome （FXS） is the most common monogenic cause of intellectual disability and a cause for autism. FXS females report milder phenotypes and a lower rate of cognitive problems compared to males. This is most likely because most females are heterozygous, while males are hemizygous for the disease. Thus, most preclinical studies have been completed in males. As there is major interest in testing experimental drugs for FXS, it is imperative to determine whether females in animal models used for research, present behavioral alterations that might translate to humans in order to confirm that experimental drugs have an effect on both genders. In our study we describe behavioral phenotypes in homozygous FXS female mice developed on the FVB.129 background. We focused on detection of hippocampal-mediated cognitive abilities and other behaviors described for FXS. Our research shows that, while female FVB.129-Fmrl knockout mice present normal learning, they have impaired memory, as well as susceptibility to audiogenic seizures. In agreement with previous reports in rodents and humans, significant levels of the small GTPase Racl were found in FXS female mice. Because Racl is involved in neuronal development, plasticity and behavior, we additionally aimed to pharmacologically inhibit Racl and determine whether observed phenotypes are rescued. Treatment of female FVB.129-Fmrl knockout with a Racl inhibitor abolished behavioral deficits, bringing phenotypes to control levels. Our results suggest that female FVB.129-Fmrl knockout mice display behavioral impairments that resemble FXS in humans. Moreover, those behavioral shortfalls might be associated with alteration of plasticity involving excessive Racl function, since pharmacological reduction of Racl normalizes previously altered phenotypes to control levels.

Genome-wide CRISPR screen identifies synthetic lethality between DOCK1 inhibition and metformin in liver cancer

Metformin is currently a strong candidate anti-tumor agent in multiple cancers.However,its anti-tumor effectiveness varies among different cancers or sub-populations,potentially due to tumor heterogeneity.It thus remains unclear which hepatocellular carcinoma(HCC)patient subpopulation(s)can benefit from met-formin treatment.Here,through a genome-wide CRISPR-Cas9-based knockout screen,we find that DOCK1 levels determine the anti-tumor effects of met-formin and that DOCK1 is a synthetic lethal target of metformin in HCC.Mechanistically,metformin promotes DOCK1 phosphorylation,which activates RAC1 to facilitate cell survival,leading to metformin resistance.The DOCK1-selective inhibitor,TBOPP,potentiates anti-tumor activity by metformin in vitro in liver cancer cell lines and patient-derived HCC organoids,and in vivo in xenografted liver cancer cells and immunocompetent mouse liver cancer models.Notably,metformin improves overall survival of HCC patients with low DOCK1 levels but not among patients with high DOCK1 expression.This study shows that metformin effective-ness depends on DOCK1 levels and that combining metformin with DOCK1 inhibition may provide a promising personalized therapeutic strategy for met-formin-resistant HCC patients.

Protein trafficking during plant innate immunity

Plants have evolved a sophisticated immune system to fight against pathogenic microbes. Upon detection of pathogen invasion by immune receptors, the immune system is turned on, resulting in production of antimicrobial molecules including pathogenesis-related（PR） proteins.Conceivably, an efficient immune response depends on the capacity of the plant cell＇s protein/membrane trafficking network to deploy the right defense-associated molecules in the right place at the right time. Recent research in this area shows that while the abundance of cell surface immune receptors is regulated by endocytosis, many intracellular immune receptors, when activated, are partitioned between the cytoplasm and the nucleus for induction of defense genes and activation of programmed cell death, respectively. Vesicle transport is an essential process for secretion of PR proteins to the apoplastic space and targeting of defense-related proteins to the plasma membrane or other endomembrane compartments. In this review, we discuss the various aspects of protein trafficking during plant immunity, with a focus on the immunity proteins on the move and the major components of the trafficking machineries engaged.

Inactivation of Cdc42 in embryonic brain results in hydrocephalus with ependymal cell defects in mice

The establishment of a polarized cellular morphology is essential for a variety of processes including neural tube morphogenesis and the development of the brain.Cdc42 is a Ras-related GTPase that plays an essential role in controlling cell polarity through the regulation of the actin and microtubule cytoskeleton architecture.Previous studies have shown that Cdc42 plays an indispensable role in telencephalon development in earlier embryo developmental stage(before E12.5).However,the functions of Cdc42 in other parts of brain in later embryo developmental stage or in adult brain remain unclear.Thus,in order to address the role of Cdc42 in the whole brain in later embryo developmental stage or in adulthood,we used Cre/loxP technology to generate two lines of tissue-specific Cdc42-knock-out mice.Inactivation of Cdc42 was achieved in neuroepithelial cells by crossing Cdc42/flox mice with Nestin-Cre mice and resulted in hydrocephalus,causing death to occur within the postnatal stage.Histological analyses of the brains from these mice showed that ependymal cell differentiation was disrupted,resulting in aqueductal stenosis.Deletion of Cdc42 in the cerebral cortex also induced obvious defects in interki-netic nuclear migration and hypoplasia.To further explore the role of Cdc42 in adult mice brain,we examined the effects of knocking-out Cdc42 in radial glial cells by crossing Cdc42/flox mice with human glial fi brillary acidic protein(GFAP)-Cre mice.Inactivation of Cdc42 in radial glial cells resulted in hydrocephalus and ependymal cell denudation.Taken together,these results highlight the importance of Cdc42 for ependymal cell differentiation and maintaining,and suggest that these functions likely contribute to the essential roles played by Cdc42 in the development of the brain.