Nolz1 expression is required in dopaminergic axon guidance and striatal innervation.

Midbrain dopaminergic (DA) axons make long longitudinal projections towards the striatum. Despite the importance of DA striatal innervation, processes involved in establishment of DA axonal connectivity remain largely unknown. Here we demonstrate a striatal-specific requirement of transcriptional regulator Nolz1 in establishing DA circuitry formation. DA projections are misguided and fail to innervate the striatum in both constitutive and striatal-specific Nolz1 mutant embryos. The lack of striatal Nolz1 expression results in nigral to pallidal lineage conversion of striatal projection neuron subtypes. This lineage switch alters the composition of secreted factors influencing DA axonal tract formation and renders the striatum non-permissive for dopaminergic and other forebrain tracts. Furthermore, transcriptomic analysis of wild-type and Nolz1-/- mutant striatal tissue led to the identification of several secreted factors that underlie the observed guidance defects and proteins that promote DA axonal outgrowth. Together, our data demonstrate the involvement of the striatum in orchestrating dopaminergic circuitry formation.

SOX2 Regulates P63 and Stem/Progenitor Cell State in the Corneal Epithelium.

Mutations in key transcription factors SOX2 and P63 were linked with developmental defects and postnatal abnormalities such as corneal opacification, neovascularization, and blindness. The latter phenotypes suggest that SOX2 and P63 may be involved in corneal epithelial regeneration. Although P63 has been shown to be a key regulator of limbal stem cells, the expression pattern and function of SOX2 in the adult cornea remained unclear. Here, we show that SOX2 regulates P63 to control corneal epithelial stem/progenitor cell function. SOX2 and P63 were co-expressed in the stem/progenitor cell compartments of the murine cornea in vivo and in undifferentiated human limbal epithelial stem/progenitor cells in vitro. In line, a new consensus site that allows SOX2-mediated regulation of P63 enhancer was identified while repression of SOX2 reduced P63 expression, suggesting that SOX2 is upstream to P63. Importantly, knockdown of SOX2 significantly attenuated cell proliferation, long-term colony-forming potential of stem/progenitor cells, and induced robust cell differentiation. However, this effect was reverted by forced expression of P63, suggesting that SOX2 acts, at least in part, through P63. Finally, miR-450b was identified as a direct repressor of SOX2 that was required for SOX2/P63 downregulation and cell differentiation. Altogether, we propose that SOX2/P63 pathway is an essential regulator of corneal stem/progenitor cells while mutations in SOX2 or P63 may disrupt epithelial regeneration, leading to loss of corneal transparency and blindness. Stem Cells 2019;37:417-429.

miRNAs-19b, -29b-2* and -339-5p show an early and sustained up-regulation in ischemic models of stroke.

Stroke, the loss of neurons after ischemic insult to the brain, is one of the leading causes of death and disability worldwide. Despite its prevalence and severity, current therapy is extremely limited, highlighting the importance of further understanding the molecular events underlying ischemia-induced neuronal cell death. An ischemic area can be subdivided into two separate pathophysiological regions: the rapidly dying necrotic core, and the potentially salvageable apoptotic penumbra. Understanding molecular events occurring in the apoptotic ischemic penumbra may give greater insight into mechanisms controlling this salvageable tissue. miRNAs are known to have key roles in the regulation of gene expression in numerous pathological conditions, including the modulation of distinct pathways in stroke. However, previous studies have profiled miRNAs in the whole ischemic infarct, and do not differentiate between miRNA regulation in the necrotic core versus the apoptotic penumbra. We asked if there were unique miRNAs that are differentially regulated following ischemic insults in the salvageable apoptotic penumbra. miRNA expression profiles were compared in the whole infarct from in vivo stroke models, using the three vessel occlusion approach, to an in vitro model of the ischemic penumbra, prior to apoptotic induction. Multiple miRNAs were found to be differentially regulated following ischemic insults in each system. However, miR-19b, miR-29b-2* and miR-339-5p were significantly up-regulated in both model systems. Further, we confirmed these results in a neuroblastoma cell line subjected to a penumbra-like ischemic insult that induced the apoptotic cell death pathway. The data show that miR-19b, miR-29b-2* and miR-339-5p are up-regulated following ischemic insults and may be regulating gene expression to control important cellular pathways in the salvageable ischemic penumbra. Further investigation of their role and mRNA target identification may lead to new insights into the molecular mechanisms taking place in the salvageable apoptotic penumbra.

Mitochondrial fragmentation and neuronal cell death in response to the Bcl-2/Bcl-x(L)/Bcl-w antagonist ABT-737.

Inhibition of pro-survival Bcl-2 family proteins by BH3-only proteins is a key initial step leading to apoptotic cell death. In neurons, investigating cell death pathways is often hampered by the multi-factorial nature of the stress stimuli employed. Here we investigate the action of ABT-737, a small molecule inhibitor which specifically targets the BH3-protein binding domain of pro-survival Bcl-2, Bcl-X(L) and Bcl-w. ABT-737 produced a time- and concentration-dependent neuronal cell death which displayed the classical hallmarks of apoptosis. Cell death was maximal by around 4 h ABT-737 treatment, and the effect of ABT-737 could be delayed by the broad spectrum caspase inhibitor zVADfmk. Examining, using real-time confocal microscopy, the molecular basis for the onset of response demonstrated recruitment of pro-apoptotic Bax to specific mitochondrial foci, followed by mitochondrial fragmentation. Treatment of neurons with ABT-737 also produced cleavage of Bid, a BH3-only protein known to be a caspase substrate. Interestingly, cleaved Bid translocated to mitochondria but did not colocalise with Bax foci. zVADfmk inhibited Bid cleavage and slowed the rate of fragmentation, suggesting a role for cleaved Bid in the amplification of the apoptotic response. siRNA-mediated knockdown of Bax significantly inhibited ABT-737 induced cell death, whereas knockdown of the BH3-only proteins Bid or Bim had no effect. ABT-737 therefore appears to be a useful tool with which to examine neuronal apoptotic pathways. Our data suggests that caspase-dependent cleavage of Bid may be a downstream amplification event which enhances the rate of mitochondrial fragmentation.