Dbx1 controls the development of astrocytes of the intermediate spinal cord by modulating Notch signaling.

Significant progress has been made in elucidating the basic principles that govern neuronal specification in the developing central nervous system. In contrast, much less is known about the origin of astrocytic diversity. Here, we demonstrate that a restricted pool of progenitors in the mouse spinal cord, expressing the transcription factor Dbx1, produces a subset of astrocytes, in addition to interneurons. Ventral p0-derived astrocytes (vA0 cells) exclusively populate intermediate regions of spinal cord with extraordinary precision. The postnatal vA0 population comprises gray matter protoplasmic and white matter fibrous astrocytes and a group of cells with strict radial morphology contacting the pia. We identified that vA0 cells in the lateral funiculus are distinguished by the expression of reelin and Kcnmb4. We show that Dbx1 mutants have an increased number of vA0 cells at the expense of p0-derived interneurons. Manipulation of the Notch pathway, together with the alteration in their ligands seen in Dbx1 knockouts, suggest that Dbx1 controls neuron-glial balance by modulating Notch-dependent cell interactions. In summary, this study highlights that restricted progenitors in the dorsal-ventral neural tube produce region-specific astrocytic subgroups and that progenitor transcriptional programs highly influence glial fate and are instrumental in creating astrocyte diversity.

Lipids modulate the increase of BK channel calcium sensitivity by the ß1 subunit.

Co-expression of the auxiliary ß1 subunit with the pore forming α subunit of BK dramatically alters apparent calcium sensitivity. Investigation of the mechanism underlying the increase in calcium sensitivity of BK in smooth muscle has concentrated on the energetic effect of ß1's interaction with α. We take a novel approach, exploring whether ß1 modification of calcium sensitivity reflects altered interaction between the channel protein and surrounding lipids. We reconstituted hSlo BK α and BK α+ß1 channels into two sets of bilayers. One set contained POPE with POPS, POPG, POPA and POPC, where the length of acyl chains is constant, but surface charge differs. The second set is a series of neutral bilayers formed from DOPE with phosphatidylcholines (PCs) of varying acyl chain lengths: C (14:1), C (18:1), C (22:1) and C (24:1), and with brain sphingomyelin (SPM), in which surface charge is constant, but bilayer thickness varies. The increase in calcium sensitivity caused by the ß1 subunit was preserved in negatively charged lipid bilayers but not in neutral bilayers, indicating that modification of apparent Ca(2+) sensitivity by ß1 is modulated by membrane lipids, requiring negatively charged lipids in the membrane. Moreover, the presence of ß1 reduces BK activity in thin bilayers of PC 14:1 and thick bilayers containing SPM, but has no significant effect on activity of BK in PC 18:1, PC 22:1 and PC 24:1 bilayers. These data suggest that auxiliary ß1 subunits fine-tune channel gating not only through direct subunit-subunit interactions but also by modulating lipid-protein interactions.

Structural determinants for functional coupling between the beta and alpha subunits in the Ca2+-activated K+ (BK) channel.

High conductance, calcium- and voltage-activated potassium (BK, MaxiK) channels are widely expressed in mammals. In some tissues, the biophysical properties of BK channels are highly affected by coexpression of regulatory (beta) subunits. The most remarkable effects of beta1 and beta2 subunits are an increase of the calcium sensitivity and the slow down of channel kinetics. However, the detailed characteristics of channels formed by alpha and beta1 or beta2 are dissimilar, the most remarkable difference being a reduction of the voltage sensitivity in the presence of beta1 but not beta2. Here we reveal the molecular regions in these beta subunits that determine their differential functional coupling with the pore-forming alpha-subunit. We made chimeric constructs between beta1 and beta2 subunits, and BK channels formed by alpha and chimeric beta subunits were expressed in Xenopus laevis oocytes. The electrophysiological characteristics of the resulting channels were determined using the patch clamp technique. Chimeric exchange of the different regions of the beta1 and beta2 subunits demonstrates that the NH3 and COOH termini are the most relevant regions in defining the behavior of either subunit. This strongly suggests that the intracellular domains are crucial for the fine tuning of the effects of these beta subunits. Moreover, the intracellular domains of beta1 are responsible for the reduction of the BK channel voltage dependence. This agrees with previous studies that suggested the intracellular regions of the alpha-subunit to be the target of the modulation by the beta1-subunit.