Chia, J. | bioRxiv Science

bioRxiv2018

The GalNAc-T Activation (GALA) Pathway: Drivers and Markers

The enzymes GALNTs add GalNAc sugar to Ser and Thr residues, forming the Tn glycan. GALNTs are activated by trafficking from Golgi to ER, a process driven by the Src kinase and negatively regulated by ERK8. This GALNTs activation (aka GALA) pathway induces high Tn levels and is a key driver of liver tumor growth. Recently, Tabak and colleagues have contested our previous data that EGF stimulation can induce GALNTs relocation. Here, we show that relocation induced by EGF is actually detectable in the images acquired by Tabak et al. Furthermore, we show that expression of EGFR enhances relocation and appears required to drive relocation induced by ERK8 depletion. We also propose that quantification of O-glycosylation of the ER resident protein PDIA4 provides an alternative measure of GALA. In sum, we demonstrate that non-reproducibility was due to experimental errors, that EGFR is indeed a driver of GALA and propose additional markers to facilitate the study of this pathway.

cell biology↗

bioRxiv2016

Loss of the habenula neuromodulator Kisspeptin1 disrupts learning

Learning how to actively avoid a predictable aversive stimulus involves two steps: recognizing the cue that predicts upcoming punishment, and learning a behavioral response that will lead to avoidance. In zebrafish, ventral habenula (vHb) neurons have been proposed to participate in both steps by encoding the expected aversiveness of a stimulus. vHb neurons increase their firing rate as expectation of punishment grows, but reduce their activity as avoidance learning occurs. How the change in vHb activity occurs is not known. Here, we ask whether the neuromodulator kisspeptin1, which is expressed in the ventral habenula, could be involved. Kiss1 mutants were generated with Cas9 using guide RNAs targeted to the signal sequence. Mutants, which have a stop codon upstream of the kisspeptin1 peptide, have a deficiency in learning to avoid a shock that is predicted by light. Electrophysiology indicates that kisspeptin1 has a concentration-dependent effect on vHb neurons: depolarizing at low concentrations and hyperpolarizing at high concentrations. These data suggest that as the fish learns to cope with a threat, kisspeptin1 may differentially modulate vHb neurons. This implies that learning a behavioral strategy to overcome a stressor is accompanied by physiological change in habenula neurons.\n\nSignificance statementLearning to deal with adversity can positively affect ones ability to cope with challenges in the immediate future. Control thus causes short-term change in the brain. Here, we show that the neuromodulator kisspeptin1 is required to learn to avoid a punishment. Expression and electrophysiological recordings suggest that this molecule functions by controlling the ventral habenula, a region of the brain that mediates fear by regulating serotonin release. Kisspeptin1 may be a potential player in resilience developed as a result of control, extending previous findings that it can reduce fear.

animal behavior and cognition↗