Faculty Bibliography

The receptor for activated C-kinase (RACK1) is a scaffold protein that is able to interact simultaneously with several signalling molecules. It binds to protein kinases and membrane-bound receptors in a regulated fashion. Interestingly, RACK1 is also a constituent of the eukaryotic ribosome, and a recent cryo-electron microscopy study localized it to the head region of the 40S subunit in the vicinity of the messenger RNA (mRNA) exit channel. RACK1 recruits activated protein kinase C to the ribosome, which leads to the stimulation of translation through the phosphorylation of initiation factor 6 and, potentially, of mRNA-associated proteins. RACK1 therefore links signal-transduction pathways directly to the ribosome, which allows translation to be regulated in response to cell stimuli. In addition, the fact that RACK1 associates with membrane-bound receptors indicates that it promotes the docking of ribosomes at sites where local translation is required, such as focal adhesions

OBJECTIVE: To investigate the effects of standard meal and fat meal distending the fundus on transient lower esophageal sphincter relaxation (TLESR) and esophageal motility and to explore the mechanism of gastroesophageal reflux (GER) in patients with gastroesophageal reflux disease (GERD). METHODS: Eight patients with GERD (3 male, 5 female; median age: 43.5 ys) were enrolled in the study. All received 2 times of esophageal manometry and pH monitoring simultaneously for 30 min during fasting and 2 h after two different test-meals, including standard meal (SM) and fat meal (FM) on separate day at least 1 week apart. RESULTS: The frequency of TLESR significantly increased after 2 test-meals (P < 0.05). There were no significant difference in the frequency and duration of TLESR between SM group and FM group 1 h after meal (P > 0.05). However, the frequency of TLESR in FM group 2 h after meal was more than that in SM group and during fasting (P < 0.05). Lower esophageal sphincter pressure (LESP) significantly decreased in FM group than in SM group (P < 0.05). The contractive amplitude of post lower esophageal sphincter relaxation and the contractive amplitude of the distal esophagus had no difference after FM and SM. Acid reflux episodes and duration of pH < 4 were larger after FM than after SM (P < 0.05). A total of 50.2% of GER occurred during decreased LESP and 37.8% during TLESR after FM, while 61.7% of GER occurred during TLESR after SM. CONCLUSIONS: Both the SM and FM can increase the frequency of TLESR in patients with GERD. Decreased LESP and increased frequency of TLESR after FM are the major mechanism of GER, while reflux after SM may attribute to the increased frequency of TLESR.

The lowermost portion of the resting (telogen) follicle consists of the bulge and secondary hair germ. We previously showed that the progeny of stem cells in the bulge form the lower follicle and hair, but the relationship of the bulge cells with the secondary hair germ cells, which are also involved in the generation of the new hair at the onset of the hair growth cycle (anagen), remains unclear. Here we address whether secondary hair germ cells are derived directly from epithelial stem cells in the adjacent bulge or whether they arise from cells within the lower follicle that survive the degenerative phase of the hair cycle (catagen). We use 5-bromo-2'-deoxyuridine to label bulge cells at anagen onset, and demonstrate that the lowermost portion of the bulge collapses around the hair and forms the secondary hair germ during late catagen. During the first six days of anagen onset bulge cells proliferate and self-renew. Bulge cell proliferation at this time also generates cells that form the future secondary germ. As bulge cells form the secondary germ cells at the end of catagen, they lose expression of a biochemical marker, S100A6. Remarkably, however, following injury of bulge cells by hair depilation, progenitor cells in the secondary hair germ repopulate the bulge and re-express bulge cell markers. These findings support the notion that keratinocytes can 'dedifferentiate' to a stem cell state in response to wounding, perhaps related to signals from the stem cell niche. Finally, we also present evidence that quiescent bulge cells undergo apoptosis during follicle remodeling in catagen, indicating that a subpopulation of bulge cells is not permanent

In Alzheimer's disease (AD), the neuropathologic hallmarks of beta-amyloid deposition and neurofibrillary degeneration are associated with early and progressive pathology of the endosomal-lysosomal system. Abnormalities of autophagy, a major pathway to lysosomes for protein and organelle turnover, include marked accumulations of autophagy-related vesicular compartments (autophagic vacuoles or AVs) in affected neurons. Here, we investigated the possibility that AVs contain the proteases and substrates necessary to cleave the amyloid precursor protein (APP) to A beta peptide that forms beta-amyloid, a key pathogenic factor in AD. AVs were highly purified using a well-established metrizamide gradient procedure from livers of transgenic YAC mice overexpressing wild-type human APP. By Western blot analysis, AVs contained APP, beta C

Given the importance of genetically modified mice in studies of mammalian brain development and human congenital brain diseases, MRI has the potential to provide an efficient in vivo approach for analyzing mutant phenotypes in the early postnatal mouse brain. The combination of reduced tissue contrast at the high magnetic fields required for mice, and the changing cellular composition of the developing mouse brain make it difficult to optimize MRI contrast in neonatal mouse imaging. We have explored an easily implemented approach for contrast-enhanced imaging, using systemically administered manganese (Mn) to reveal fine anatomical detail in T1-weighted MR images of neonatal mouse brains. In particular, we demonstrate the utility of this Mn-enhanced MRI (MEMRI) method for analyzing early postnatal patterning of the mouse cerebellum. Through comparisons with matched histological sections, we further show that MEMRI enhancement correlates qualitatively with granule cell density in the developing cerebellum, suggesting that the cerebellar enhancement is due to uptake of Mn in the granule neurons. Finally, variable cerebellar defects in mice with a conditional mutation in the Gbx2 gene were analyzed with MEMRI to demonstrate the utility of this method for mutant mouse phenotyping. Taken together, our results indicate that MEMRI provides an efficient and powerful in vivo method for analyzing neonatal brain development in normal and genetically engineered mice

The mesencephalic/rhombomere 1 border (isthmus) is an organizing center for early development of midbrain and cerebellum. In this review, we summarize recent progress in studies of Fgf signaling in the isthmus and discuss how the isthmus instructs the differentiation of the midbrain versus cerebellum. Fgf8 is shown to play a pivotal role in isthmic organizer activity. Only a strong Fgf signal mediated by Fgf8b activates the Ras-extracellular signal-regulated kinase (ERK) pathway, and this is sufficient to induce cerebellar development. A lower level of signaling transduced by Fgf8a, Fgf17 and Fgf18 induce midbrain development. Numerous feedback loops then maintain appropriate mesencephalon/rhombomere1 and organizer gene expression

The hematopoietic system consists of more than ten differentiated cell types, all of which are derived from a single type of hematopoietic stem cell. The accessibility and interest of this system have made it a model for understanding normal and abnormal differentiation of mammalian cells. Newer techniques have generated a mass of data that requires integrative approaches for analysis and interpretation. The traditional view of the differentiation program holds that a small number of regulators are involved in each stage of cell specification. However, this may not be the case. Recent analyses have shown that almost all substantial subsets of genes, including the set of broadly expressed transcription factors, are expressed in patterns that are unique for each lineage. Further, much of this difference between lineages can be captured in two-dimensional graphs. Understanding the biologic significance, mechanisms and constraints underlying these differences is a challenge for experimentalists and computational biologists alike

In vitro studies suggest a role for c-Jun N-terminal kinases (JNKs) in proatherogenic cellular processes. We show that atherosclerosis-prone ApoE-/- mice simultaneously lacking JNK2 (ApoE-/- JNK2-/- mice), but not ApoE-/- JNK1-/- mice, developed less atherosclerosis than do ApoE-/- mice. Pharmacological inhibition of JNK activity efficiently reduced plaque formation. Macrophages lacking JNK2 displayed suppressed foam cell formation caused by defective uptake and degradation of modified lipoproteins and showed increased amounts of the modified lipoprotein-binding and -internalizing scavenger receptor A (SR-A), whose phosphorylation was markedly decreased. Macrophage-restricted deletion of JNK2 was sufficient to decrease atherogenesis. Thus, JNK2-dependent phosphorylation of SR-A promotes uptake of lipids in macrophages, thereby regulating foam cell formation, a critical step in atherogenesis

Neuronal plasticity relies on tightly regulated control of protein levels at synapses. One mechanism to control protein abundance is the ubiquitin-proteasome degradation system. Recent studies have implicated ubiquitin-mediated protein degradation in synaptic development, function, and plasticity, but little is known about the regulatory mechanisms controlling ubiquitylation in neurons. In contrast, ubiquitylation has long been studied as a central regulator of the eukaryotic cell cycle. A critical mediator of cell-cycle transitions, the anaphase-promoting complex/cyclosome (APC/C), is an E3 ubiquitin ligase. Although the APC/C has been detected in several differentiated cell types, a functional role for the complex in postmitotic cells has been elusive. We describe a novel postmitotic role for the APC/C at Drosophila neuromuscular synapses: independent regulation of synaptic growth and synaptic transmission. In neurons, the APC/C controls synaptic size via a downstream effector Liprin-alpha; in muscles, the APC/C regulates synaptic transmission, controlling the concentration of a postsynaptic glutamate receptor.

We have developed a versatile statistical analysis algorithm for the detection of genomic aberrations in human cancer cell lines. The algorithm analyzes genomic data obtained from a variety of array technologies, such as oligonucleotide array, bacterial artificial chromosome array, or array-based comparative genomic hybridization, that operate by hybridizing with genomic material obtained from cancer and normal cells and allow detection of regions of the genome with altered copy number. The number of probes (i.e., resolution), the amount of uncharacterized noise per probe, and the severity of chromosomal aberrations per chromosomal region may vary with the underlying technology, biological sample, and sample preparation. Constrained by these uncertainties, our algorithm aims at robustness by using a priorless maximum a posteriori estimator and at efficiency by a dynamic programming implementation. We illustrate these characteristics of our algorithm by applying it to data obtained from representational oligonucleotide microarray analysis and array-based comparative genomic hybridization technology as well as to synthetic data obtained from an artificial model whose properties can be varied computationally. The algorithm can combine data from multiple sources and thus facilitate the discovery of genes and markers important in cancer, as well as the discovery of loci important in inherited genetic disease