Unravelling HP1 functions: post-transcriptional regulation of stem cell fate

Heterochromatin protein 1 (HP1) is a non-histone chromosomal protein first identified in Drosophila as a major component of constitutive heterochromatin, required for stable epigenetic gene silencing in many species including humans. Over the years, several studies have highlighted additional roles of HP1 in different cellular processes including telomere maintenance, DNA replication and repair, chromosome segregation and, surprisingly, positive regulation of gene expression. In this review, we briefly summarize past research and recent results supporting the unexpected and emerging role of HP1 in activating gene expression. In particular, we discuss the role of HP1 in post-transcriptional regulation of mRNA processing because it has proved decisive in the control of germline stem cells homeostasis in Drosophila and has certainly added a new dimension to our understanding on HP1 targeting and functions in epigenetic regulation of stem cell behaviour.

Control of Early B Cell Development by the RNA N6-Methyladenosine Methylation

The RNA N⁶-methyladenosine (m⁶A) methylation is installed by the METTL3-METTL14 methyltransferase complex. This modification has critical regulatory roles in various biological processes. Here, we report that deletion of Mettl14 dramatically reduces mRNA m⁶A methylation in developing B cells and severely blocks B cell development in mice. Deletion of Mettl14 impairs interleukin-7 (IL-7)-induced pro-B cell proliferation and the large-pre-B-to-small-pre-B transition and causes dramatic abnormalities in gene expression programs important for B cell development. Suppression of a group of transcripts by cytoplasmic m⁶A reader YTHDF2 is critical to the IL-7-induced pro-B cell proliferation. In contrast, the block in the large-pre-B-to-small-pre-B transition is independent of YTHDF1 or YTHDF2 but is associated with a failure to properly upregulate key transcription factors regulating this transition. Our data highlight the important regulatory roles of the RNA m⁶A methylation and its reader proteins in early B cell development.

Post-transcriptional control of the mammalian circadian clock: implications for health and disease

Many aspects of human physiology and behavior display rhythmicity with a period of approximately 24 h. Rhythmic changes are controlled by an endogenous time keeper, the circadian clock, and include sleep-wake cycles, physical and mental performance capability, blood pressure, and body temperature. Consequently, many diseases, such as metabolic, sleep, autoimmune and mental disorders and cancer, are connected to the circadian rhythm. The development of therapies that take circadian biology into account is thus a promising strategy to improve treatments of diverse disorders, ranging from allergic syndromes to cancer. Circadian alteration of body functions and behavior are, at the molecular level, controlled and mediated by widespread changes in gene expression that happen in anticipation of predictably changing requirements during the day. At the core of the molecular clockwork is a well-studied transcription-translation negative feedback loop. However, evidence is emerging that additional post-transcriptional, RNA-based mechanisms are required to maintain proper clock function. Here, we will discuss recent work implicating regulated mRNA stability, translation and alternative splicing in the control of the mammalian circadian clock, and its role in health and disease.

Regulation of gene expression in mammalian nervous system through alternative pre-mRNA splicing coupled with RNA quality control mechanisms

Eukaryotic gene expression is orchestrated on a genome-wide scale through several post-transcriptional mechanisms. Of these, alternative pre-mRNA splicing expands the proteome diversity and modulates mRNA stability through downstream RNA quality control (QC) pathways including nonsense-mediated decay (NMD) of mRNAs containing premature termination codons and nuclear retention and elimination (NRE) of intron-containing transcripts. Although originally identified as mechanisms for eliminating aberrant transcripts, a growing body of evidence suggests that NMD and NRE coupled with deliberate changes in pre-mRNA splicing patterns are also used in a number of biological contexts for deterministic control of gene expression. Here we review recent studies elucidating molecular mechanisms and biological significance of these gene regulation strategies with a specific focus on their roles in nervous system development and physiology. This article is part of a Special Issue entitled 'RNA and splicing regulation in neurodegeneration'.