Spatiotemporal regulation of NADP(H) phosphatase Nocturnin and its role in oxidative stress response.

An intimate link exists between circadian clocks and metabolism with nearly every metabolic pathway in the mammalian liver under circadian control. Circadian regulation of metabolism is largely driven by rhythmic transcriptional activation of clock-controlled genes. Among these output genes, Nocturnin (Noct) has one of the highest amplitude rhythms at the mRNA level. The Noct gene encodes a protein (NOC) that is highly conserved with the endonuclease/exonuclease/phosphatase (EEP) domain-containing CCR4 family of deadenylases, but highly purified NOC possesses little or no ribonuclease activity. Here, we show that NOC utilizes the dinucleotide NADP(H) as a substrate, removing the 2' phosphate to generate NAD(H), and is a direct regulator of oxidative stress response through its NADPH 2' phosphatase activity. Furthermore, we describe two isoforms of NOC in the mouse liver. The cytoplasmic form of NOC is constitutively expressed and associates externally with membranes of other organelles, including the endoplasmic reticulum, via N-terminal glycine myristoylation. In contrast, the mitochondrial form of NOC possesses high-amplitude circadian rhythmicity with peak expression level during the early dark phase. These findings suggest that NOC regulates local intracellular concentrations of NADP(H) in a manner that changes over the course of the day.

COE loss-of-function analysis reveals a genetic program underlying maintenance and regeneration of the nervous system in planarians.

Members of the COE family of transcription factors are required for central nervous system (CNS) development. However, the function of COE in the post-embryonic CNS remains largely unknown. An excellent model for investigating gene function in the adult CNS is the freshwater planarian. This animal is capable of regenerating neurons from an adult pluripotent stem cell population and regaining normal function. We previously showed that planarian coe is expressed in differentiating and mature neurons and that its function is required for proper CNS regeneration. Here, we show that coe is essential to maintain nervous system architecture and patterning in intact (uninjured) planarians. We took advantage of the robust phenotype in intact animals to investigate the genetic programs coe regulates in the CNS. We compared the transcriptional profiles of control and coe RNAi planarians using RNA sequencing and identified approximately 900 differentially expressed genes in coe knockdown animals, including 397 downregulated genes that were enriched for nervous system functional annotations. Next, we validated a subset of the downregulated transcripts by analyzing their expression in coe-deficient planarians and testing if the mRNAs could be detected in coe+ cells. These experiments revealed novel candidate targets of coe in the CNS such as ion channel, neuropeptide, and neurotransmitter genes. Finally, to determine if loss of any of the validated transcripts underscores the coe knockdown phenotype, we knocked down their expression by RNAi and uncovered a set of coe-regulated genes implicated in CNS regeneration and patterning, including orthologs of sodium channel alpha-subunit and pou4. Our study broadens the knowledge of gene expression programs regulated by COE that are required for maintenance of neural subtypes and nervous system architecture in adult animals.