Satb2 is a DNA-binding protein that regulates chromatin organization and gene expression. In the developing brain, Satb2 is expressed in cortical neurons that extend axons across the corpus callosum. To assess the role of Satb2 in neurons, we analyzed mice in which the Satb2 locus was disrupted by insertion of a LacZ gene. In mutant mice, beta-galactosidase-labeled axons are absent from the corpus callosum and instead descend along the corticospinal tract. Satb2 mutant neurons acquire expression of Ctip2, a transcription factor that is necessary and sufficient for the extension of subcortical projections by cortical neurons. Conversely, ectopic expression of Satb2 in neural stem cells markedly decreases Ctip2 expression. Finally, we find that Satb2 binds directly to regulatory regions of Ctip2 and induces changes in chromatin structure. These data suggest that Satb2 functions as a repressor of Ctip2 and regulatory determinant of corticocortical connections in the developing cerebral cortex.

Vertebrate skeletogenesis involves two processes, skeletal patterning and osteoblast differentiation. Here, we show that Satb2, encoding a nuclear matrix protein, is expressed in branchial arches and in cells of the osteoblast lineage. Satb2-/- mice exhibit both craniofacial abnormalities that resemble those observed in humans carrying a translocation in SATB2 and defects in osteoblast differentiation and function. Multiple osteoblast-specific genes were identified as targets positively regulated by SATB2. In addition, SATB2 was found to repress the expression of several Hox genes including Hoxa2, an inhibitor of bone formation and regulator of branchial arch patterning. Molecular analysis revealed that SATB2 directly interacts with and enhances the activity of both Runx2 and ATF4, transcription factors that regulate osteoblast differentiation. This synergy was genetically confirmed by bone formation defects in Satb2/Runx2 and Satb2/Atf4 double heterozygous mice. Thus, SATB2 acts as a molecular node in a transcriptional network regulating skeletal development and osteoblast differentiation.

Non-technical summary Blood flow in the kidney is tightly regulated. This so-called autoregulation is essential for the function of the kidney as well as for its protection against damage and failure from high blood pressure. Autoregulation is caused by three mechanisms. The signalling molecule nitric oxide (NO) modulates the balance of these mechanisms, blunting the contribution of the fastest mechanism and increasing that of the others. What is unknown is where in the kidney the responsible NO is originating. Our data indicate that the cells of the inner lining of the blood vessels are by far the most important source of NO for this effect compared to other NO-producing cells in the relevant region of the kidney, such as macula densa, smooth muscle or mesangial cells. The findings are important for understanding blood flow autoregulation in the kidney as well as kidney function and failure.Abstract Nitric oxide (NO) blunts the myogenic response (MR) in renal blood flow (RBF) autoregulation. We sought to clarify the roles of NO synthase (NOS) isoforms, i.e. neuronal NOS (nNOS) from macula densa, endothelial NOS (eNOS) from the endothelium, and inducible NOS (iNOS) from smooth muscle or mesangium. RBF autoregulation was studied in rats and knockout (ko) mice in response to a rapid rise in renal artery pressure (RAP). The autoregulatory rise in renal vascular resistance within the first 6 s was interpreted as MR, from ∼6 to ∼30 s as tubuloglomerular feedback (TGF), and ∼30 to ∼100 s as the third regulatory mechanism. In rats, the nNOS inhibitor SMTC did not significantly affect MR (67 ± 4 vs. 57 ± 4 units). Inhibition of all NOS isoforms by L-NAME in the same animals markedly augmented MR to 78 ± 4 units. The same was found when SMTC was combined with angiotensin II to reproduce the hypertension and vasoconstriction seen with L-NAME (58 ± 3 vs. 54 ± 7 units, L-NAME 81 ± 2 units), or when SMTC was replaced by the nNOS inhibitor NPA (57 ± 5 vs. 56 ± 7 units, L-NAME 79 ± 4 units) or by the iNOS inhibitor 1400W (50 ± 1 vs. 55 ± 4 units, L-NAME 81 ± 3 units). nNOS-ko mice showed the same autoregulation as wild-types (MR 36 ± 4 vs. 38 ± 3 units) and the same response to L-NAME (111 ± 9 vs. 114 ± 10 units). eNOS-ko had similar autoregulation as wild-types (44 ± 8 vs. 33 ± 4 units), but failed to respond to L-NAME (37 ± 7 vs. 78 ± 16 units). We conclude that the attenuating effect of NO on MR depends on eNOS, but not on nNOS or iNOS. In eNOS-ko mice MR is depressed by NO-independent means.

-We studied the influence of soluble guanylate (sGC) on renal blood flow (RBF), glomerular filtration rate (GFR), and RBF autoregulation and its role in mediating the hemodynamic effects of endogenous nitric oxide (NO). Arterial pressure (AP), heart rate (HR), RBF, GFR, urine flow (UV), and the efficiency and mechanisms of RBF autoregulation were studied in anesthetized rats during intravenous infusion of sGC activator cinaciguat before and (except GFR) also after inhibition of NO synthase (NOS) by N -nitro-L-arginine methyl ester. Cinaciguat (0.1, 0.3, 1, 3, 10 g·kg Ϫ1 ·min Ϫ1 , n ϭ 7) reduced AP and increased HR, but did not significantly alter RBF. In clearance experiments (FITC-sinistrin, n ϭ 7) GFR was not significantly altered by cinaciguat (0.1 and 1 g·kg Ϫ1 ·min Ϫ1 ), but RBF slightly rose (ϩ12%) and filtration fraction (FF) fell (Ϫ23%). RBF autoregulatory efficiency (67 vs. 104%) and myogenic response (33 vs. 44 units) were slightly depressed (n ϭ 9). NOS inhibition (n ϭ 7) increased AP (ϩ38 mmHg), reduced RBF (Ϫ53%), and greatly augmented the myogenic response in RBF autoregulation (97 vs. 35 units), attenuating the other regulatory mechanisms. These changes were reversed by 77, 78, and 90% by 1 g·kg Ϫ1 ·min Ϫ1 cinaciguat. In vehicle controls (n ϭ 3), in which cinaciguat-induced hypotension was mimicked by aortic compression, the NOS inhibition-induced changes were not affected. We conclude that sGC activation leaves RBF and GFR well maintained despite hypotension and only slightly impairs autoregulation. The ability to largely normalize AP, RBF, RBF autoregulation, and renovascular myogenic response after NOS inhibition indicates that these hemodynamic effects of NO are predominantly mediated via sGC.