Light-induced Notch activity controls neurogenic and gliogenic potential of neural progenitors.

Oscillations in Notch signaling are essential for reserving neural progenitors for cellular diversity in developing brains. Thus, steady and prolonged overactivation of Notch signaling is not suitable for generating neurons. To acquire greater temporal control of Notch activity and mimic endogenous oscillating signals, here we adopted a light-inducible transgene system to induce active form of Notch NICD in neural progenitors. Alternating Notch activity saved more progenitors that are prone to produce neurons creating larger number of mixed clones with neurons and progenitors in vitro, compared to groups with no light or continuous light stimulus. Furthermore, more upper layer neurons and astrocytes arose upon intermittent Notch activity, indicating that dynamic Notch activity maintains neural progeny and fine-tune neuron-glia diversity.

Radiosurgery inhibition of the Notch signaling pathway in a rat model of arteriovenous malformations.

OBJECT: Notch signaling has been suggested to promote the development and maintenance of arteriovenous malformations (AVMs), but whether radiosurgery inhibits Notch signaling pathways in AVMs is unknown. The aim of this study was to examine molecular changes of Notch signaling pathways following radiosurgery and to explore mechanisms of radiosurgical obliteration of "nidus" vessels in a rat model of AVMs. METHODS: One hundred eleven rats received common carotid artery-to-external jugular vein anastomosis to form an arteriovenous fistula (AVF) model. Six weeks postoperatively, dilated small vessels and capillaries formed a nidus. The rats with AVFs received 25-Gy radiosurgery. The expression of Notch1 and Notch4 receptors and their ligands, Delta-like1 and Delta-like4, Jagged1, Notch downstream gene target HES1, and an apoptotic marker caspase-3 in nidus vessels in the AVF rats was examined immunohistochemically and was quantified using LAS-AF software at 7 time points over a period of 42 days postradiosurgery. The interaction events between Notch1 receptor and Jagged1, as well as Notch4 receptor and Jagged1, were quantified in nidus vessels in the AVF rats using proximity ligation assay at different time points over 42 days postradiosurgery. RESULTS: The expression of Notch1 and Notch4 receptors, Delta-like1, Delta-like4, Jagged1, and HES1 was observed in nidus vessels in the AVF rats pre- and postradiosurgery. Radiosurgery enhanced apoptotic activity (p < 0.05) and inhibited the expression of Notch1 and Notch4 receptors and Jagged1 in the endothelial cells of nidus vessels in the AVF rats at 1, 2, 3, 7, 21, 28, and 42 days postradiosurgery (p < 0.05). Radiosurgery suppressed the interaction events between Notch1 receptor and Jagged1 (p < 0.001) as well as Notch4 receptor and Jagged1 (p < 0.001) in the endothelial cells of nidus vessels in the AVF rats over a period of 42 days postradiosurgery. Radiosurgery induced thrombotic occlusion of nidus vessels in the AVF rats. There was a positive correlation between the percentage of fully obliterated nidus vessels and time after radiosurgery (r = 0.9324, p < 0.001). CONCLUSIONS: Radiosurgery inhibits endothelial Notch1 and Notch4 signaling pathways in nidus vessels while inducing thrombotic occlusion of nidus vessels in a rat model of AVMs. The underlying mechanisms of radiosurgery-induced AVM shrinkage could be a combination of suppressing Notch receptor signaling in blood vessel endothelial cells, leading to a reduction in nidus vessel size and thrombotic occlusion of nidus vessels.

Photoexposition discriminates Notch 1 expression in human cutaneous squamous cell carcinoma.

The Notch signaling pathway may play opposing roles in cancer. It can be oncosuppressive or protumoral, depending on the cellular and tissue context. In skin cancer, Notch 1 expression is downregulated, thus supporting the hypothesis of an oncosuppressive role in cutaneous carcinomas. However, as members of the Notch family undergo downregulation upon exposure to UV irradiation, we wondered whether Notch 1 expression in skin carcinomas may be governed by additional factors, including UV exposure. We investigated the expression of Notch 1 and its ligands, Jagged 1, Jagged 2 and Delta-like 1, by immunohistochemistry in a series of premalignant and invasive cutaneous carcinomas, including 4 solar keratoses, 5 Bowen's disease, 5 squamous cell carcinomas on sun-exposed skin, 6 squamous cell carcinomas on sun-protected genital skin and 14 basal cell carcinomas of different histotypes (nodular, superficial type, sclerodermiform/infiltrating and baso-squamous). Expression of Notch 1 was decreased in solar keratoses and invasive squamous cell carcinomas localized on sun-exposed skin. In contrast, marked Notch 1 staining was observed in extragenital Bowen's disease as well as in genital (penile) human papilloma virus-related in situ and invasive squamous cell carcinomas. A diffuse Notch 1 staining was detected in nodular and superficial basal cell carcinomas while sclerodermiform/infiltrating and baso-squamous basal cell carcinomas showed a low to absent Notch 1 expression. Jagged 1, Jagged 2 and Delta-like 1 proteins were expressed in all tissues examined. Present findings show divergent expression of Notch 1 in skin cancer, depending on anatomical site and tumor histotype. Thus, whereas in UV-related squamous cell photocarcinogenesis Notch 1 downregulation could mirror a tumor suppressor function of the receptor, in sun-protected squamous cell carcinomas Notch 1 was upregulated. Furthermore, Notch 1 expression was minimal in basal cell carcinoma subtypes correlated with risk of recurrence (sclerodermiform/infiltrating and baso-squamous) in comparison with nodular and superficial types.

Early response of neural stem/progenitor cells after X-ray irradiation in vitro.

We investigated the effect of oxidative stress on cell cycle regulation of neural stem/progenitor cells in neurosphere culture. We exposed murine neural stem/progenitor cells to 2 Gy of X-ray irradiation at 48 h after first passage. We found that G2 and G1-arrested cells increased at 3 and 12 h after X-ray irradiation, respectively by using laser scanning cytometer. We revealed that such G2 and G1 arrests were correlated with phosphorylation of cdc2 and p53, respectively by Western blotting analysis. Furthermore, we found that the effects of X-ray irradiation of neural stem/progenitor cells involved inactivation of Notch signal. These results suggest that the drastic response of neural stem/progenitor cells after X-ray irradiation occurred even in the short period.