Reviews & Analysis

The non-canonical addition of non-templated nucleotides to RNA 3′ ends (tailing) by terminal nucleotidyltransferases includes uridylation, mixed-nucleotide tailing and post-transcriptional polyadenylation. Recent studies of human terminal nucleotidyltransferases have revealed their distinct specificities for substrates, including mRNAs, microRNAs and other non-coding RNAs, and how they control RNA stability and activity.

Extracellular vesicles transfer a variety of cellular components between cells — including proteins, lipids and nucleic acids. There is now evidence indicating that these cargoes, in particular RNAs, can affect the function of recipient cells. Extracellular vesicles are now being actively tested as biomarkers and delivery vehicles for therapeutic agents.

The unfolded protein response (UPR) comprises a network of signalling pathways that reprogramme transcription, translation and protein modifications to relieve the load of unfolded or misfolded proteins in the endoplasmic reticulum lumen and restore proteostasis. Understanding the regulation of the UPR and the role it has in the pathophysiology of various cell types and organs might open new therapeutic avenues.

The cyclic GMP–AMP synthase (cGAS)–stimulator of interferon genes (STING) pathway senses DNA in the cytoplasm, whether of pathogenic or endogenous (chromatin or mitochondrial) origin, and triggers the interferon response. The mechanisms of DNA recognition and cGAS–STING activation and signalling are now coming into focus, providing insights into the cellular functions of this pathway, including interferon-independent roles.

Autophagy involves engulfment of cellular components into double-membrane vesicles called autophagosomes. The biogenesis of autophagosomes requires the cooperation of multiple proteins and lipids from various membrane sources. Our understanding of the molecular mechanisms of the initiation, growth, bending and closure of autophagosomal membranes is expanding at a rapid pace.

Circular RNAs, which are produced through back-splicing of exons, are emerging as key regulators of immune responses and cell proliferation. Recent studies have shed new light on the biogenesis and functions of circular RNAs, which include the modulation of transcription and splicing, and interference with microRNAs and other cellular signalling pathways.

G-quadruplexes (G4s) are structures formed in guanine-rich DNA or RNA, which are linked to transcription, translation, chromatin biology, genome instability and RNA modifications. Recent studies connect G4 formation with cancer-cell lethality and indicate that G4s could be therapeutic targets.

Development and homeostasis are dependent on rapid cell turnover, achieved by the programmed death and subsequent engulfment and breakdown of cells, a process known as efferocytosis. Defects in efferocytosis have been linked to a wide range of diseases; ongoing research therefore aims to better understand efferocytosis processes so as to uncover new therapeutic targets.

Telomere length is maintained by telomerase, which comprises a reverse transcriptase and a template RNA. Telomerase activity is disrupted in several genetic disorders, but is commonly increased in cancer. Recent studies have uncovered many regulatory mechanisms of telomerase and how telomerase upregulation in cancer is achieved.

Cells maximize the repertoire of functions produced from their genome through introducing diversity at each stage of the gene expression process, including at the post-translational level. New advances in proteomics and interactomics have begun to shed light on the extent to which diversity is introduced on the proteome level and by the organization of proteins into modular interaction networks.

Reactive oxygen species (ROS) were originally associated with cellular damage and disease. However, ROS, notably hydrogen peroxide, at low physiological levels also engage in physiological signalling, supporting cellular responses and adaptation to changing environments and stress. Accordingly, controlling specific ROS-mediated signalling pathways offers new perspectives for a more refined redox medicine.

The transcriptional response to hypoxia and the role of hypoxia inducible factors have been extensively studied. Yet, hypoxic cells also adapt to hypoxia by modulating protein synthesis, metabolism and nutrient uptake. Understanding these processes could shed light on pathologies associated with hypoxia, including cardiovascular diseases and cancer, and disease mechanisms, such as inflammation and wound repair.

The mechanical and dynamic properties of microtubules are determined by their complement of subunits, known as tubulin isotypes, and the post-translational modifications found on these isotypes. This concept is known as the ‘tubulin code’. The regulation of microtubules and microtubule-associated proteins by this code is critical for the correct function of a range of tissues. Consequently, recent studies have linked perturbation of the tubulin code to disease, including neurodegenerative diseases.

BRCA1 and its partner BARD1 support repair of double-strand breaks by homologous recombination and protect replication forks from damage. Recent studies have improved our understanding of the molecular mechanisms of these tumour-suppressive functions of BRCA1–BARD1 and how they are subverted in therapy-resistant cancers.

Mitochondrial networks are dynamically remodelled via fusion, fission and ultrastructural changes to mitochondrial membranes. These mitochondrial membrane dynamics are tightly coupled to cell function, with morphological changes to mitochondria accompanying a multitude of processes as diverse as cell pluripotency, division, differentiation, senescence and death. Accordingly, disturbed dynamics of mitochondrial membranes are linked to severe human disorders.

The MYC oncoproteins are transcription factors, but the molecular mechanism of their oncogenic activity is unclear. MYC proteins promote transcription termination in stress conditions, which is proposed to increase cellular resilience to stress and to promote tumorigenesis independently of changes in the expression of their target genes.

During cell division, the distribution of membrane-bound organelles needs to be tightly regulated to ensure the proper composition and function of daughter cells. Recent studies have shed light on the range of complex and dynamic mechanisms needed to mediate organelle inheritance and membrane remodelling during cell division.

Mammalian genomes generate long non-coding RNAs, which are degraded by the RNA surveillance machinery. This regulated degradation is vital for various processes, including for genome integrity, stem cell pluripotency and immune cell activation. Consequently, defects in RNA surveillance cause human diseases and developmental disorders.

Ageing is characterized by the functional decline of tissues and organs and increased risk of ageing-associated disorders, and this decline is associated with epigenetic changes. Recently, ‘rejuvenating’ interventions, such as metabolic manipulation, partial cell reprogramming, heterochronic parabiosis and senescent cell ablation, have been proposed to extend healthspan and lifespan by modulating the epigenome.

The mTOR pathway integrates diverse environmental cues to control biomass accumulation and metabolism by modulating key cellular processes, including protein synthesis and autophagy. Dysregulation of mTOR signalling has been implicated in metabolic disorders, neurodegeneration, cancer and ageing, and is thus a promising target for pharmacological intervention.