Differentiation of PC12 Cells Results in Enhanced VIP Expression and Prolonged Rhythmic Expression of Clock Genes

The Relevance of Circadian Clocks to Stem Cell Differentiation and Cancer Progression

The molecular mechanism of circadian clocks depends on transcription-translation feedback loops (TTFLs) that have known effects on key cellular processes. However, the distinct role of circadian TTFLs in mammalian stem cells and other less differentiated cells remains poorly understood. Neural stem cells (NSCs) of the brain generate neurons and glia postnatally but also may become cancer stem cells (CSCs), particularly in astrocytomas. Evidence indicates clock TTFL impairment is needed for tumor growth and progression; although, this issue has been examined primarily in more differentiated cancer cells rather than CSCs. Similarly, few studies have examined circadian rhythms in NSCs. After decades of research, it is now well recognized that tumors consist of CSCs and a range of other cancer cells along with noncancerous stromal cells. The circadian properties of these many contributors to tumor properties and treatment outcome are being widely explored. New molecular tools and ones in development will likely enable greater discrimination of important circadian and non-circadian cells within malignancies at multiple stages of cancer progression and following therapy. Here, we focus on adult NSCs and glioma CSCs to address how cells at different stages of differentiation may harbor unique states of the molecular circadian clock influencing differentiation and cell fate.

FOS proliferating network construction in early colorectal cancer (CRC) based on integrative significant function cluster and inferring analysis

The aim is to setup single distinguished molecular network. We constructed FOS proliferating network from 22 colorectal samples of the same GEO dataset by GRNInfer tool and DAVID based on linear programming and a decomposition procedure with integrated Kappa statistics and fuzzy heuristic clustering. In the control, we found no proliferating subnetwork. In CRC, we identified one FOS proliferating module (SFRP2, ADAMTS1, SYNPO2, VIP, ADAM33 inhibition to FOS and MGP, FOSB activation to FOS. FOS activation to IGFBP5, LGI1, GAS1 and FOS inhibition to VIP). These results may be useful for developing novel prognostic markers and therapeutic targets in CRC.

N-linked deglycosylated melanopsin retains its responsiveness to light

Melanopsin is an opsin expressed in the plasma membrane of retinal ganglion cells that mainly project to the circadian clock and thus is important for nonvisual responses to light. Rat melanopsin contains two potential sites (Asn31 and Asn35) for N-linked glycosylation in the N-terminal extracellular part. To investigate if melanopsin is N-linked glycosylated and whether N-bound glycans influence the response of melanopsin to light as evidenced by Fos mRNA induction, we transfected PC12 cells to stably express rat wild-type melanopsin or mutant melanopsin lacking both N-linked glycosylation sites. Immunoblotting for membrane-bound melanopsin from the PC12 cells transfected to express wild-type melanopsin disclosed two immunoreactive bands of 62 and 49 kDa. Removal of N-linked glycosylation by tunicamycin or PNGase F changed the 62 kDa band to a 55 kDa band, while the 49 kDa band corresponding to the core melanopsin protein was unaffected. Likewise, mutation of the two extracellular N-linked glycosylation sites gave a melanopsin size comparable to that of PNGase F or tunicamycin treatment (55 kDa). Further in vitro O-linked deglycosylation of wild-type or mutant melanopsin with O-glycosidase and neuraminidase converted the 55 kDa band to a 49 kDa band. Finally, neither in vivo N-linked deglycosylation nor mutations of the two N-linked glycosylation sites significantly affected melanopsin function measured by Fos induction after light stimulation. In conclusion, we have shown that heterologously expressed rat melanopsin is both N-linked and O-linked glycosylated and that N-linked glycosylation is not crucial for the melanopsin response to light.

Clock genes regulate neurogenic transcription factors, including NeuroD1, and the neuronal differentiation of adult neural stem/progenitor cells

The circadian clock system plays multiple roles in our bodies, and clock genes are expressed in various brain regions, including the lateral subventricular zone (SVZ) where neural stem/progenitor cells (NSPCs) persist and postnatal neurogenesis continues. However, the functions of clock genes in adult NSPCs are not well understood. Here, we first investigated the expression patterns of Clock and Bmal1 in the SVZ by immunohistochemistry and then verified how the expression levels of 17 clock and clock-related genes changed during differentiation of cultured adult NSPCs using quantitative RT-PCR. Finally, we used RNAi to observe the effects of Clock and Bmal1 on neuronal differentiation. Our results revealed that Clock and Bmal1 were expressed in the SVZ and double-stained with the neural progenitor marker Nestin and neural stem marker GFAP. In cultured adult NSPCs, the clock genes changed their expression patterns during differentiation, and interestingly, Bmal1 started endogenous oscillation. Moreover, gene silencing of Clock or Bmal1 by RNAi decreased the percentages of neuronal marker Map2-positive cells and expression levels of NeuroD1 mRNA. These findings suggest that clock genes are involved in the neuronal differentiation of adult NSPCs and may extend our understanding of various neurological/psychological disorders linked to adult neurogenesis and circadian rhythm.