The nuclear receptor tailless is required for neurogenesis in the adult subventricular zone

The tailless (Tlx) gene encodes an orphan nuclear receptor that is expressed by neural stem/progenitor cells in the adult brain of the subventricular zone (SVZ) and the dentate gyrus (DG). The function of Tlx in neural stem cells of the adult SVZ remains largely unknown. We show here that in the SVZ of the adult brain Tlx is exclusively expressed in astrocyte-like B cells. An inducible mutation of the Tlx gene in the adult brain leads to complete loss of SVZ neurogenesis. Furthermore, analysis indicates that Tlx is required for the transition from radial glial cells to astrocyte-like neural stem cells. These findings demonstrate the crucial role of Tlx in the generation and maintenance of NSCs in the adult SVZ in vivo.

The nuclear receptor tailless induces long-term neural stem cell expansion and brain tumor initiation

Malignant gliomas are the most common primary brain tumors, and are associated with frequent resistance to therapy as well as poor prognosis. Here we demonstrate that the nuclear receptor tailless (Tlx), which in the adult is expressed exclusively in astrocyte-like B cells of the subventricular zone, acts as a key regulator of neural stem cell (NSC) expansion and brain tumor initiation from NSCs. Overexpression of Tlx antagonizes age-dependent exhaustion of NSCs in mice and leads to migration of stem/progenitor cells from their natural niche. The increase of NSCs persists with age, and leads to efficient production of newborn neurons in aged brain tissues. These cells initiate the development of glioma-like lesions and gliomas. Glioma development is accelerated upon loss of the tumor suppressor p53. Tlx-induced NSC expansion and gliomagenesis are associated with increased angiogenesis, which allows for the migration and maintenance of brain tumor stem cells in the perivascular niche. We also demonstrate that Tlx transcripts are overexpressed in human primary glioblastomas in which Tlx expression is restricted to a subpopulation of nestin-positive perivascular tumor cells. Our study clearly demonstrates how NSCs contribute to brain tumorgenesis driven by a stem cell-specific transcription factor, thus providing novel insights into the histogenesis and molecular pathogenesis of primary brain tumors.

High and low affinity binding of [3H]cholate to rat liver plasma membranes

The transport of bile acids across sinusoidal and canalicular membranes of hepatocytes is characterized as carrier mediated. Such a carrier should specifically bind bile acids at physiological concentrations. We examined the binding of [3H]cholate to rat liver plasma membranes using a microcentrifugation technique and detected high (KD = 1.23 +/- 0.44 microM, Bmax = 21.8 +/- 3.3 pmol/mg protein) and low (KD = 1.97 +/- 1.33 mM, Bmax = 41.5 +/- 25.3 nmol/mg protein) affinity binding sites. Maximal binding was achieved within 15-45 sec and was stable for 2 min at 37 degrees. Binding to the high affinity site was reversible, was not Na+ dependent or attributable to vesicular uptake, and exhibited a broad pH optimum. Binding to this site was negligible or not detected in liver mitochondrial and microsomal fractions, was saturable, and was inhibited by other bile acids. The IC50 values for bile acids as inhibitors of [3H]cholate binding at the high affinity site were: taurocholate, 1.9 nM; glycodeoxycholate, 3.1 nM; chenodeoxycholate, 5.6 nM; taurochenodeoxycholate, 7.3 nM; glycochenodeoxycholate, 11 nM; lithocholate, 13 nM; taurodeoxycholate, 20 nM; glycocholate, 3.6 microM; and deoxycholate, 5.6 microM. [3H]Cholate specific binding was inhibited by 10(-5) M bromosulfophthalein, bilirubin and indocyanin green. These data support the hypothesis that the high affinity binding site represents a carrier which is shared by bile acids and nonbile acid organic anions.

Lipocalin 13 enhances insulin secretion but is dispensable for systemic metabolic control

Thorough preclinical evaluation reveals a negligible role of lipocalin 13 in systemic glucose and lipid metabolism.

Members of the lipocalin protein family serve as biomarkers for kidney disease and acute phase inflammatory reactions, and are under preclinical development for the diagnosis and therapy of allergies. However, none of the lipocalin family members has made the step into clinical development, mostly due to their complex biological activity and the lack of in-depth mechanistic knowledge. Here, we show that the hepatokine lipocalin 13 (LCN13) triggers glucose-dependent insulin secretion and cell proliferation of primary mouse islets. However, inhibition of endogenous LCN13 expression in lean mice did not alter glucose and lipid homeostasis. Enhanced hepatic secretion of LCN13 in either diet-induced or genetic obesity led to no discernible impact on systemic glucose and lipid metabolism, neither in preventive nor therapeutic setting. Of note, loss or forced LCN13 hepatic secretion did not trigger any compensatory regulation of related lipocalin family members. Together, these data are in stark contrast to the suggested gluco-regulatory and therapeutic role of LCN13 in obesity, and imply complex regulatory steps in LCN13 biology at the organismic level mitigating its principal insulinotropic effects.