No abstract

Summary NeuroD, an insulin transactivator, is critical for development of the endocrine pancreas, and NeuroD mutations cause MODY6 in humans. To investigate the role of NeuroD in differentiated β cells, we generated mice in which neuroD is deleted in insulin-expressing cells. These mice exhibit severe glucose intolerance. Islets lacking NeuroD respond poorly to glucose and display a glucose metabolic profile similar to immature β cells, featuring increased expression of glycolytic genes and LDH-A, elevated basal insulin secretion and O2 consumption, and overexpression of NPY. Moreover, the mutant islets appear to have defective KATP channel-mediated insulin secretion. Unexpectedly, virtually all insulin in the mutant mice is derived from ins2, whereas ins1 expression is almost extinguished. Overall, these results indicate that NeuroD is required for β cell maturation and demonstrate the importance of NeuroD in the acquisition and maintenance of fully functional glucose responsive β cells.

Intraperitoneal administration of the cytokine interleukin-1␤ (IL-1␤) induces brain-mediated sickness symptoms that can be blocked by subdiaphragmatic vagotomy. Intraperitoneal IL-1␤ also induces expression of the activation marker c-fos in vagal primary afferent neurons, suggesting that IL-1␤ is a key component of vagally mediated immune-to-brain communication.The cellular sources of IL-1␤ activating the vagus are unknown, but may reside in either blood or in the vagus nerve itself. We assayed IL-1␤ protein after intraperitoneal endotoxin [lipopolysaccharide (LPS)] injection in abdominal vagus nerve, using both an ELISA and immunohistochemistry, and in blood plasma using ELISA. IL-1␤ levels in abdominal vagus nerve increased by 45 min after LPS administration and were robust by 60 min. Plasma IL-1␤ levels increased by 60 min, whereas little IL-1␤ was detected in cervical vagus or sciatic nerve. IL-1␤-immunoreactivity (IR) was expressed in dendritic cells and macrophages within connective tissues associated with the abdominal vagus by 45 min after intraperitoneal LPS injection. By 60 min, some immune cells located within the nerve and vagal paraganglia also expressed IL-1␤-IR. Thus, intraperitoneal LPS induced IL-1␤ protein within the vagus in a time-frame consistent with signaling of immune activation. These results suggest a novel mechanism by which IL-1␤ may serve as a molecular link between the immune system and vagus nerve, and thus the CNS.

Retinal precursor cells give rise to six types of neurons and one type of glial cell during development, and this process is controlled by multiple basic helix-loophelix (bHLH) genes. However, the precise mechanism for specification of retinal neuronal subtypes, particularly horizontal neurons and photoreceptors, remains to be determined. Here, we examined retinas with three different combinations of triple bHLH gene mutations. In retinas lacking the bHLH genes Ngn2, Math3, and NeuroD, horizontal neurons as well as other neurons such as bipolar cells were severely decreased in number. In the retina lacking the bHLH genes Mash1, Ngn2, and Math3, horizontal and other neurons were severely decreased, whereas ganglion cells were increased. In the retina lacking the bHLH genes Mash1, Math3, and NeuroD, photoreceptors were severely decreased, whereas ganglion cells were increased. In all cases, glial cells were increased. The increase and decrease of these cells were the result of cell fate changes and cell death and seem to be partly attributable to the remaining bHLH gene expression, which also changes because of triple bHLH gene mutations. These results indicate that multiple bHLH genes cross-regulate each other, cooperatively specify neuronal subtypes, and regulate neuronal survival in the developing retina.In the neural retina, there are six types of neurons and one type of glial cell forming three cellular layers as follows: (i) rod and cone photoreceptors in the outer nuclear layer (ONL) 1 ; (ii) horizontal, bipolar, and amacrine interneurons and Mü ller glia in the inner nuclear layer (INL); and (iii) ganglion and displaced amacrine cells in the ganglion cell layer (GCL). During retinal development, these seven types of cells are generated from common precursors in sequences relatively conserved among species (1, 2); ganglion cells are generated first, followed in overlapping phases by horizontal cells, cones, amacrine cells, rods, bipolar cells and, finally, Mü ller glial cells. The retina is a good model system for investigating the mechanism of neural development because it has a relatively simple structure and mimics normal development in isolated explant cultures.It has been shown that retinal cell fate determination and differentiation are controlled by intrinsic cues, such as transcription factors, and extrinsic signals, such as neurotrophic factors (3-6). The basic helix-loop-helix (bHLH) genes are good candidates for intrinsic regulators of retinal cell fate decision (7-9). In the developing mammalian eye, neurogenic bHLH genes such as Mash1, Math3, Math5, Ngn2, and NeuroD are expressed by retinal precursor cells (10 -16). Loss of function studies indicate that these bHLH genes play an essential role in specification of many retinal cell types. For example, in the absence of Math5, ganglion cells are severely decreased, whereas amacrine cells are increased, indicating that Math5

Neurod1 is a crucial basic helix-loop-helix gene for most cerebellar granule cells and mediates the differentiation of these cells downstream of Atoh1-mediated proliferation of the precursors. In Neurod1 null mice, granule cells die throughout the posterior two thirds of the cerebellar cortex during development. However, Neurod1 is also necessary for pancreatic β-cell development, and therefore Neurod1 null mice are diabetic, which potentially influences cerebellar defects. Here, we report a new Neurod1 conditional knock-out mouse model created by using a Tg(Atoh1-cre) line to eliminate Neurod1 in the cerebellar granule cell precursors. Our data confirm and extend previous work on systemic Neurod1 null mice and show that, in the central lobules, granule cells can be eradicated in the absence of Neurod1. Granule cells in the anterior lobules are partially viable and depend on as yet unknown genes, but the Purkinje cells show defects not previously recognized. Interestingly, delayed and incomplete Tg(Atoh1-cre) upregulation occurs in the most posterior lobules; this leads to near normal expression of Neurod1 with a concomitant normal differentiation of granule cells, Purkinje cells, and unipolar brush cells in lobules IX and X. Our analysis suggests that Neurod1 negatively regulates Atoh1 to ensure a rapid transition from proliferative precursors to differentiating neurons. Our data have implications for research on medulloblastoma, one of the most frequent brain tumors of children, as the results suggest that targeted overexpression of Neurod1 under Atoh1 promoter control may initiate the differentiation of these tumors.