ABSTRACT
The neuromodulator dopamine plays a significant role in light adaptation, eye growth, and modulation of neuronal circuitry in the retina. Dopaminergic amacrine cells in the adult retina release dopamine in response to light stimulation, however, the light-induced activity of these cells in during postnatal development is not known. We assessed the activity of dopaminergic amacrine cells in the retina response to a light pulse in C57BL/6 wild-type animals across various postnatal ages. Expression of tyrosine hydroxylase (TH) in dopaminergic amacrine cells was apparent from postnatal day 3 (P3) and restricted to the dorso-temporal region; by P8 TH+ cells were uniformly distributed across the retina. TH cell density increased until P8 and then markedly decreased by P10 to then remain at this density into adulthood. Light-induced c-fos expression was observed in all light-pulsed retinae, however, no c-fos was ever found to be co-localised with TH prior to P12. At P14, one day after eye opening, 100% of TH cells co-localised with c-fos and this was maintained for all older ages analysed. Dopamine and its primary metabolite DOPAC were measured in the vitreous of animals P8-P30. Both analytes were found in the vitreous at all ages, however, a significant difference in dopamine concentration between dark and light-pulsed animals was only observed at P30. DOPAC concentration was found to be significantly light-induced from P16, and the amplitude of this difference increased over time. Our data suggests that dopaminergic cell activation and light-induced dopamine release in the retina is primarily driven by classical photoreceptors after eye-opening.
ABSTRACT
MMSET/WHSC1 is a histone methyltransferase (HMT) overexpressed in t(4;14)+ multiple myeloma (MM) patients, believed to be the driving factor in the pathogenesis of this MM subtype. MMSET overexpression in MM leads to an increase in histone 3 lysine 36 dimethylation (H3K36me2), and a decrease in histone 3 lysine 27 trimethylation (H3K27me3), as well as changes in proliferation, gene expression and chromatin accessibility. Prior work linked methylation of histones to the ability of cells to undergo DNA damage repair. In addition, t(4;14)+ patients frequently relapse after regimens that include DNA damage-inducing agents, suggesting that MMSET may play a role in DNA damage repair and response. In U2OS cells, we found that MMSET is required for efficient non-homologous end joining as well as homologous recombination. Loss of MMSET led to loss of expression of several DNA repair proteins, as well as decreased recruitment of DNA repair proteins to sites of DNA double-strand breaks (DSBs). By using genetically matched MM cell lines that had either high (pathological) or low (physiological) expression of MMSET, we found that MMSET-high cells had increased damage at baseline. Upon addition of a DNA-damaging agent, MMSET-high cells repaired DNA damage at an enhanced rate and continued to proliferate, whereas MMSET-low cells accumulated DNA damage and entered cell cycle arrest. In a murine xenograft model using t(4;14)+ KMS11 MM cells harboring an inducible MMSET shRNA, depletion of MMSET enhanced the efficacy of chemotherapy, inhibiting tumor growth and extending survival. These findings help explain the poorer prognosis of t(4;14) MM and further validate MMSET as a potential therapeutic target in MM and other cancers.
