Probes for CRE

Ageing is intimately connected to the induction of cell senescence1,2, but why this is so remains poorly understood. A key challenge is the identification of pathways that normally suppress senescence, are lost during ageing and are functionally relevant to oppose ageing3. Here we connected the structural and functional decline of ageing tissues to attenuated function of the master effectors of cellular mechanosignalling YAP and TAZ. YAP/TAZ activity declines during physiological ageing in stromal cells, and mimicking such decline through genetic inactivation of YAP/TAZ in these cells leads to accelerated ageing. Conversely, sustaining YAP function rejuvenates old cells and opposes the emergence of ageing-related traits associated with either physiological ageing or accelerated ageing triggered by a mechano-defective extracellular matrix. Ageing traits induced by inactivation of YAP/TAZ are preceded by induction of tissue senescence. This occurs because YAP/TAZ mechanotransduction suppresses cGAS-STING signalling, to the extent that inhibition of STING prevents tissue senescence and premature ageing-related tissue degeneration after YAP/TAZ inactivation. Mechanistically, YAP/TAZ-mediated control of cGAS-STING signalling relies on the unexpected role of YAP/TAZ in preserving nuclear envelope integrity, at least in part through direct transcriptional regulation of lamin B1 and ACTR2, the latter of which is involved in building the peri-nuclear actin cap. The findings demonstrate that declining YAP/TAZ mechanotransduction drives ageing by unleashing cGAS-STING signalling, a pillar of innate immunity. Thus, sustaining YAP/TAZ mechanosignalling or inhibiting STING may represent promising approaches for limiting senescence-associated inflammation and improving healthy ageing.

Neuregulin 1 (NRG1) is a trophic factor that has been implicated in neural development, neurotransmission, and synaptic plasticity. NRG1 has multiple isoforms that are generated by usage of different promoters and alternative splicing of a single gene. However, little is known about NRG1 isoform composition profile, whether it changes during development, or the underlying mechanisms. We found that each of the six types of NRG1 has a distinct expression pattern in the brain at different ages, resulting in a change in NRG1 isoform composition. In both human and rat, the most dominant are types III and II, followed by either type I or type V, while types IV and VI are the least abundant. The expression of NRG1 isoforms is higher in rat brains at ages of E13 and P5 (in particular type V), suggesting roles in early neural development and in the neonatal critical period. At the cellular level, the majority of NRG1 isoforms (types I, II, and III) are expressed in excitatory neurons, although they are also present in GABAergic neurons and astrocytes. Finally, the expression of each NRG1 isoform is distinctly regulated by neuronal activity, which causes significant increase in type I and IV NRG1 levels. Neuronal activity regulation of type IV expression requires a CRE cis-element in the 5' untranslated region (UTR) that binds to CREB. These results indicate that expression of NRG1 isoforms is regulated by distinct mechanisms, which may contribute to versatile functions of NRG1 and pathologic mechanisms of brain disorders such as schizophrenia.

Where the gene is expressed determines the function of the gene. Neuregulin 1 (Nrg1) encodes a tropic factor and is genetically linked with several neuropsychiatry diseases such as schizophrenia, bipolar disorder and depression. Nrg1 has broad functions ranging from regulating neurodevelopment to neurotransmission in the nervous system. However, the expression pattern of Nrg1 at the cellular and circuit levels in rodent brain is not full addressed.Here we used CRISPR/Cas9 techniques to generate a knockin mouse line (Nrg1Cre/+) that expresses a P2A-Cre cassette right before the stop codon of Nrg1 gene. Since Cre recombinase and Nrg1 are expressed in the same types of cells in Nrg1Cre/+ mice, the Nrg1 expression pattern can be revealed through the Cre-reporting mice or adeno-associated virus (AAV) that express fluorescent proteins in a Cre-dependent way. Using unbiased stereology and fluorescence imaging, the cellular expression pattern of Nrg1 and axon projections of Nrg1-positive neurons were investigated.In the olfactory bulb (OB), Nrg1 is expressed in GABAergic interneurons including periglomerular (PG) and granule cells. In the cerebral cortex, Nrg1 is mainly expressed in the pyramidal neurons of superficial layers that mediate intercortical communications. In the striatum, Nrg1 is highly expressed in the Drd1-positive medium spiny neurons (MSNs) in the shell of nucleus accumbens (NAc) that project to substantia nigra pars reticulata (SNr). In the hippocampus, Nrg1 is mainly expressed in granule neurons in the dentate gyrus and pyramidal neurons in the subiculum. The Nrg1-expressing neurons in the subiculum project to retrosplenial granular cortex (RSG) and mammillary nucleus (MM). Nrg1 is highly expressed in the median eminence (ME) of hypothalamus and Purkinje cells in the cerebellum.Nrg1 is broadly expressed in mouse brain, mainly in neurons, but has unique expression patterns in different brain regions.