The Specification of Cortical Subcerebral Projection Neurons Depends on the Direct Repression of TBR1 by CTIP1/BCL11a.

The acquisition of distinct neuronal fates is fundamental for the function of the cerebral cortex. We find that the development of subcerebral projections from layer 5 neurons in the mouse neocortex depends on the high levels of expression of the transcription factor CTIP1; CTIP1 is coexpressed with CTIP2 in neurons that project to subcerebral targets and with SATB2 in those that project to the contralateral cortex. CTIP1 directly represses Tbr1 in layer 5, which appears as a critical step for the acquisition of the subcerebral fate. In contrast, lower levels of CTIP1 in layer 6 are required for TBR1 expression, which directs the corticothalamic fate. CTIP1 does not appear to play a critical role in the acquisition of the callosal projection fate in layer 5. These findings unravel a key step in the acquisition of cell fate for closely related corticofugal neurons and indicate that differential dosages of transcriptions factors are critical to specify different neuronal identities.

CoREST/LSD1 control the development of pyramidal cortical neurons.

The development of a neuron from a precursor cell comprises a complex set of steps ranging from regulation of the proliferative cycle through the acquisition of distinct morphology and functionality. How these processes are orchestrated is largely unknown. Using in utero manipulation of gene expression in the mouse embryonic cerebral cortex, we found that the transition between multipolar and bipolar stages of newborn cortical pyramidal neurons is markedly delayed by depletion of CoREST, a corepressor component of chromatin remodeling complexes. This profoundly affects the onset of their radial migration. The loss of CoREST function also perturbs the dynamics of neuronal precursor cell populations, transiently increasing the fraction of cells remaining in progenitor states, but not the acquisition of the neuronal glutamatergic fate of pyramidal cells. The function of CoREST in these processes appears to be independent of its best-known interactor, the RE-1 silencer of transcription/neural restrictive silencing factor, and requires the histone demethylase LSD1. This reveals the importance of epigenetic control in the execution of neural development programs, specifically in the cerebral cortex.

The chromatin modifying complex CoREST/LSD1 negatively regulates notch pathway during cerebral cortex development.

The development of the cerebral cortex is a dynamic and coordinated process in which cell division, cell death, migration, and differentiation must be highly regulated to acquire the final architecture and functional competence of the mature organ. Notch pathway is an important regulator of differentiation and it is essential to maintain neural stem cell (NSC) pool. Here, we studied the role of epigenetic modulators such as lysine-specific demethylase 1 (LSD1) and its interactor CoREST in the regulation of the Notch pathway activity during the development of the cerebral cortex. We found that CoREST and LSD1 interact in vitro with RBPJ-κ in the repressor complex and these proteins are released upon overexpression of Notch intracellular domain (NICD). We corroborated LSD1 and RBPJ-κ interaction in developing cerebral cortex and also found that LSD1 binds to the hes1 promoter. Knock-down of CoREST and LSD1 by in utero electroporation increases Hes1 expression in vivo and decreases Ngn2. Interestingly, we found a functional interaction between CoREST and LSD1 with Notch pathway. This conclusion is based on the observation that both the defects in neuronal migration and the increase in the number of cells expressing Sox2 and Tbr2 were associated to the knock-down of either CoREST or LSD1 and were reversed by the loss of Notch. These results demonstrate that CoREST and LSD1 downregulate the Notch pathway in the developing cerebral cortex, thus suggesting a role of epigenetic regulation in the fine tuning of cell differentiation. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1360-1373, 2016.

p27Kip1 knockdown induces proliferation in the organ of Corti in culture after efficient shRNA lentiviral transduction.

The cells in the organ of Corti do not exhibit spontaneous cell regeneration; hair cells that die after damage are not replaced. Supporting cells can be induced to transdifferentiate into hair cells, but that would deplete their numbers, therefore impairing epithelium physiology. The loss of p27Kip1 function induces proliferation in the organ of Corti, which raises the possibility to integrate it to the strategies to achieve regeneration. Nevertheless, it is not known if the extent of this proliferative potential, as well as its maintenance in postnatal stages, is compatible with providing a basis for eventual therapeutic manipulation. This is due in part to the limited success of approaches to deliver tools to modify gene expression in the auditory epithelium. We tested the hypothesis that the organ of Corti can undergo significant proliferation when efficient manipulation of the expression of regulators of the cell cycle is achieved. Lentiviral vectors were used to transduce all cochlear cell types, with efficiencies around 4 % for hair cells, 43 % in the overall supporting cell population, and 74 % within lesser epithelial ridge (LER) cells. Expression of short hairpin RNA targeting p27Kip1 encoded by the lentiviral vectors led to measurable proliferation in the organ of Corti and increase in LER cells number but not hair cell regeneration. Our results revalidate the use of lentiviral vectors in the study and in the potential therapeutic approaches for inner ear diseases, as well as demonstrate that efficient manipulation of p27Kip1 is sufficient to induce significant proliferation in the postnatal cochlea.

Angiotensin II signaling in human preadipose cells: participation of ERK1,2-dependent modulation of Akt.

The renin-angiotensin system expressed in adipose tissue has been implicated in the modulation of adipocyte formation, glucose metabolism, triglyceride accumulation, lipolysis, and the onset of the adverse metabolic consequences of obesity. As we investigated angiotensin II signal transduction mechanisms in human preadipose cells, an interplay of extracellular-signal-regulated kinases 1 and 2 (ERK1,2) and Akt/PKB became evident. Angiotensin II caused attenuation of phosphorylated Akt (p-Akt), at serine 473; the p-Akt/Akt ratio decreased to 0.5±0.2-fold the control value without angiotensin II (p<0.001). Here we report that the reduction of phosphorylated Akt associates with ERK1,2 activities. In the absence of angiotensin II, inhibition of ERK1,2 activation with U0126 or PD98059 resulted in a 2.1±0.5 (p<0.001) and 1.4±0.2-fold (p<0.05) increase in the p-Akt/Akt ratio, respectively. In addition, partial knockdown of ERK1 protein expression by the short hairpin RNA technique also raised phosphorylated Akt in these cells (the p-Akt/Akt ratio was 1.5±0.1-fold the corresponding control; p<0.05). Furthermore, inhibition of ERK1,2 activation with U0126 prevented the reduction of p-Akt/Akt by angiotensin II. An analogous effect was found on the phosphorylation status of Akt downstream effectors, the forkhead box (Fox) proteins O1 and O4. Altogether, these results indicate that angiotensin II signaling in human preadipose cells involves an ERK1,2-dependent attenuation of Akt activity, whose impact on the biological functions under its regulation is not fully understood.