GLI3 Is Required for OLIG2+ Progeny Production in Adult Dorsal Neural Stem Cells

The ventricular–subventricular zone (V-SVZ) is a postnatal germinal niche. It holds a large population of neural stem cells (NSCs) that generate neurons and oligodendrocytes for the olfactory bulb and (primarily) the corpus callosum, respectively. These NSCs are heterogeneous and generate different types of neurons depending on their location. Positional identity among NSCs is thought to be controlled in part by intrinsic pathways. However, extrinsic cell signaling through the secreted ligand Sonic hedgehog (Shh) is essential for neurogenesis in both the dorsal and ventral V-SVZ. Here we used a genetic approach to investigate the role of the transcription factors GLI2 and GLI3 in the proliferation and cell fate of dorsal and ventral V-SVZ NSCs. We find that while GLI3 is expressed in stem cell cultures from both dorsal and ventral V-SVZ, the repressor form of GLI3 is more abundant in dorsal V-SVZ. Despite this high dorsal expression and the requirement for other Shh pathway members, GLI3 loss affects the generation of ventrally-, but not dorsally-derived olfactory interneurons in vivo and does not affect trilineage differentiation in vitro. However, loss of GLI3 in the adult dorsal V-SVZ in vivo results in decreased numbers of OLIG2-expressing progeny, indicating a role in gliogenesis.

Interneuron Diversity: Toward a Better Understanding of Interneuron Development In the Olfactory System

The Drosophila olfactory system is an attractive model for exploring the wiring logic of complex neural circuits. Remarkably, olfactory local interneurons exhibit high diversity and variability in their morphologies and intrinsic properties. Although olfactory sensory and projection neurons have been extensively studied of development and wiring; the development, mechanisms for establishing diversity, and integration of olfactory local interneurons into the developing circuit remain largely undescribed. In this review, we discuss some challenges and recent advances in the study of Drosophila olfactory interneurons.

Functional Parameters of Voltage-Activated Ca2+ Currents From Olfactory Interneurons in the Antennal Lobe of Periplaneta americana

Toward our goal to better understand the physiological parameters that mediate olfactory information processing on the cellular level, voltage-activated calcium currents ( ICa) in olfactory interneurons of the antennal lobe from adult cockroaches were analyzed under two conditions: 1) in acutely dissociated cells (in vitro) and 2) in an intact brain preparation (in situ). The study included an analysis of modulatory effects of potential inorganic and organic Ca2+ channel blockers. ICa was isolated and identified using pharmacological, voltage, and ion substitution protocols. ICa consisted of two components: transient and sustained. The decay of the transient component was largely Ca2+ dependent. In vitro, ICa had an activation threshold of −50 mV with a maximal peak current at −7 mV and a half-maximal voltage ( V0.5act) for tail-current activation of −18 mV. In situ these parameters were significantly shifted to more depolarized membrane potentials: ICa activated at −40 mV with a maximal peak current at 8 mV and a V0.5act for tail-current activation of −11 mV. The sensitivity of ICa to the divalent cations Cd2+, Co2+, and Ni2+ was dose dependent. The most effective blocker was Cd2+ with an IC50 of 10−5 M followed by Ni2+ (IC50 = 3.13 × 10−3 M) and Co2+ (IC50 = 1.06 × 10−3 M). The organic channel blockers verapamil, diltiazem, and nifedipine also blocked ICa in a dose-dependent way and had differential effects on the current waveform. Verapamil blocked ICa with an IC50 of 1.5 × 10−4 M and diltiazem had an IC50 of 2.87 × 10−4 M. Nifedipine blocked ICa by 33% at a concentration of 10−4 M.