Notch signaling augments the canonical Wnt pathway to specify the size of the otic placode

The inner ear derives from a patch of ectoderm defined by expression of the transcription factor Pax2. We recently showed that this Pax2^+ ectoderm gives rise not only to the otic placode but also to the surrounding cranial epidermis, and that Wnt signaling mediates this placode-epidermis fate decision. We now present evidence for reciprocal interactions between the Wnt and Notch signaling pathways during inner ear induction. Activation of Notch1 in Pax2+ ectoderm expands the placodal epithelium at the expense of cranial epidermis, whereas loss of Notch1 leads to a reduction in the size of the otic placode. We show that Wnt signaling positively regulates Notch pathway genes such as Jag1, Notch1 and Hes1, and we have used transgenic Wnt reporter mice to show that Notch signaling can modulate the canonical Wnt pathway. Gain- and loss-of-function mutations in the Notch and Wnt pathways reveal that some aspects of otic placode development - such as Pax8 expression and the morphological thickening of the placode - can be regulated independently by either Notch or Wnt signals. Our results suggest that Wnt signaling specifies the size of the otic placode in two ways, by directly upregulating a subset of otic genes, and by positively regulating components of the Notch signaling pathway, which then act to augment Wnt signaling

NOTCH-mediated non-cell autonomous regulation of chromatin structure during senescence

Senescent cells interact with the surrounding microenvironment achieving diverse functional outcomes. We have recently identified that NOTCH1 can drive ‘lateral induction’ of a unique senescence phenotype in adjacent cells by specifically upregulating the NOTCH ligand JAG1. Here we show that NOTCH signalling can modulate chromatin structure autonomously and non-autonomously. In addition to senescence-associated heterochromatic foci (SAHF), oncogenic RAS-induced senescent (RIS) cells exhibit a massive increase in chromatin accessibility. NOTCH signalling suppresses SAHF and increased chromatin accessibility in this context. Strikingly, NOTCH-induced senescent cells, or cancer cells with high JAG1 expression, drive similar chromatin architectural changes in adjacent cells through cell–cell contact. Mechanistically, we show that NOTCH signalling represses the chromatin architectural protein HMGA1, an association found in multiple human cancers. Thus, HMGA1 is involved not only in SAHFs but also in RIS-driven chromatin accessibility. In conclusion, this study identifies that the JAG1–NOTCH–HMGA1 axis mediates the juxtacrine regulation of chromatin architecture

Notch and Senescence.

Cellular senescence, previously thought of as an autonomous tumour suppressor mechanism, is emerging as a phenotype and effector present throughout the life of an organism from embryogenesis to senile decline. Senescent cells have powerful non-autonomous effects upon multiple players within their microenvironment mainly through their secretory phenotype. How senescent cells co-ordinate numerous, sometimes functionally contrasting outputs through their secretome had previously been unclear. The Notch pathway, originally identified for its involvement in Drosophila wing development, has more recently been found to underpin diverse effects in human cancer. Here we discuss recent findings that suggest that Notch is intimately involved in the development of senescence and how it acts to co-ordinate the composition and functional effects of the senescence secretome. We also highlight the complex physical and functional interplay between Notch and p53, critical to both senescence and cancer. Understanding the interplay between Notch, p53 and senescence could allow us develop the therapeutics of the future for cancer and ageing

The persistent dynamic secrets of senescence

While the beneficial versus detrimental implications of the senescence-associated secretome remain an issue of debate, time-resolved analyses of its composition, regulatory mechanisms and functional consequences have been largely missing. The dynamic activity of NOTCH is now shown to direct two distinct senescence phenotypes, by first promoting a pro-senescent TGF-{beta}1-dependent secretome, followed by a second wave of pro-inflammatory, senescence-clearing cytokines

Mechanistic Insights into the Notch signalling pathway through Molecular Condensation

The ability of a cell to undergo cellular decisions is ingrained in the integration of cues from its local environments. One such cue is relaying information based on local cell density, neighbouring cell identity, and cell positional information. A key signalling pathway in interpreting this information is the Notch signalling pathway. It is currently poorly understood how Notch is able to play a titratable role in signal transduction as our current model does not effectively translate how fluctuations in Notch signalling lead to dynamic changes in Notch target gene expression. One potential mechanism that has recently been shown to play a role in titratable gene expression of several signalling pathways is the ability for proteins to undergo molecular condensation within living cells. To date, Notch signalling has been difficult to study because of the lack of live cell systems that allow us to study both Notch protein localization and Notch target gene expression in real-time. Using PlayBack, a system I developed that allows for cost-effective plasmid cloning, I was able to develop both a light controlled Notch construct, OptoNotch, and a Live Notch target gene promoter reporter, called Hes1-Live-RNA, to allow for both the visualization and quantification of Notch activity within living cells. Using these tools, I discovered that the Notch 1 intracellular domain forms molecular condensates which in turn positively facilitates both Notch1 target gene expression as well as facilitating Notch’s ability to regulate enhancer looping. This is the first instance of N1ICD undergoing condensation within live cells and offers a mechanism by which Notch can have a titratable effect on target gene expression

Clonal analysis of Notch1-expressing cells reveals the existence of unipotent stem cells that retain long-term plasticity in the embryonic mammary gland.

Recent lineage tracing studies have revealed that mammary gland homeostasis relies on unipotent stem cells. However, whether and when lineage restriction occurs during embryonic mammary development, and which signals orchestrate cell fate specification, remain unknown. Using a combination of in vivo clonal analysis with whole mount immunofluorescence and mathematical modelling of clonal dynamics, we found that embryonic multipotent mammary cells become lineage-restricted surprisingly early in development, with evidence for unipotency as early as E12.5 and no statistically discernable bipotency after E15.5. To gain insights into the mechanisms governing the switch from multipotency to unipotency, we used gain-of-function Notch1 mice and demonstrated that Notch activation cell autonomously dictates luminal cell fate specification to both embryonic and basally committed mammary cells. These functional studies have important implications for understanding the signals underlying cell plasticity and serve to clarify how reactivation of embryonic programs in adult cells can lead to cancer.Wellcome Trus

NOTCH SIGNALING REGULATES ADIPOGENESIS AND ENERGY METABOLISM

Evolutionarily unprepared for high caloric diets and sedentary lifestyles, humans are now unprecedentedly susceptible to obesity and its associated metabolic disorders. Obesity is resulted from malfunction of the overloaded white adipocytes, which are the primary default storage sites of energy surplus. Another two types of adipocytes can also be found in human: beige and brown adipocytes. In opposite to white adipocytes, beige and brown adipocytes ameliorate obesity by burning lipids for thermogenesis. Thus, an increase in beige/brown adipocyte content in adipose tissue, termed browning would raise energy expenditure and reduce adiposity