Melatonin mediates seasonal adjustments in immune function.

In addition to seasonal changes in reproductive function, seasonal changes in immune function are mediated by the pineal hormone, melatonin. Melatonin affects immune function both indirectly, acting through other hormones, and directly by acting on components of the immune system. Melatonin also affects tumorigenesis and tumor development. We hypothesize that many of the indirect effects of melatonin on immune function are mediated through glucocorticoids, and appear to be part of an integrated series of adaptations to manage energy. Direct effects of melatonin on immune function appear to be mediated by melatonin receptors on lymphatic tissue or on immune cells in circulation. Winter is energetically demanding and stressful; thermoregulatory demands typically increase when food availability decreases. Individuals would enjoy a survival advantage if seasonally recurring stressors could be anticipated and countered by bolstering immune function. To summarize, melatonin may be part of an integrative system to coordinate reproductive, immunologic and other physiological processes to cope successfully with energetic stressors during winter.     

Wood-eating catfishes of the genus Panaque: gut microflora and cellulolytic enzyme activities

Fresh gut contents of the wood-eating loricariid Panaque and a generalized loricariid Liposarcus sp. had enzymatic activity directed against both cellulose and hemicellulose. Aerobic cultures made from the guts of Panaque exhibited growth on a minimal salts medium containing only crystalline cellulose as a carbon source as well as on a variety of other substrates containing carbon polymers found in wood. Anaerobic cultures made from Panaque guts only grew with glucose as a carbon source. Cultures of whole gut contents grown on a yeast extract basal salts medium had significant cellulolytic activity. However, no culture of individual microbes had significant cellulolytic activity, suggesting that any cellulose breakdown which occurs in loricariid guts is by a consortium of micro-organisms. A variety of aerobes, microaerophiles and facultative anaerobes were found in the guts of Panaque ; several of these bacteria appear to be new species.     

Listeria monocytogenes Exploits Normal Host Cell Processes to Spread from Cell to Cell✪

The bacterial pathogen, Listeria monocytogenes, grows in the cytoplasm of host cells and spreads intercellularly using a form of actin-based motility mediated by the bacterial protein ActA. Tightly adherent monolayers of MDCK cells that constitutively express GFP-actin were infected with L. monocytogenes, and intercellular spread of bacteria was observed by video microscopy. The probability of formation of membrane-bound protrusions containing bacteria decreased with host cell monolayer age and the establishment of extensive cell-cell contacts. After their extension into a recipient cell, intercellular membrane-bound protrusions underwent a period of bacterium-dependent fitful movement, followed by their collapse into a vacuole and rapid vacuolar lysis. Actin filaments in protrusions exhibited decreased turnover rates compared with bacterially associated cytoplasmic actin comet tails. Recovery of motility in the recipient cell required 1-2 bacterial generations. This delay may be explained by acid-dependent cleavage of ActA by the bacterial metalloprotease, Mpl. Importantly, we have observed that low levels of endocytosis of neighboring MDCK cell surface fragments occurs in the absence of bacteria, implying that intercellular spread of bacteria may exploit an endogenous process of paracytophagy.     

Development of restoration techniques for Hawaiian thrushes: Collection of wild eggs,artificial incubation,hand‐rearing,captive‐breeding,and re‐introduction to the wild

From 1995 to 1999, two species of endemic Hawaiian thrushes, `Oma`o (Myadestes obscurus) and Puaiohi (M. palmeri), were captive‐reared and re‐introduced into their historic range in Hawai`i by The Peregrine Fund, in collaboration with the U.S. Geological Survey–Biological Resources Division (BRD) and the Hawai`i State Department of Land and Natural Resources. This paper describes the management techniques that were developed (collection of wild eggs, artificial incubation, hand‐rearing, captive propagation, and release) with the non‐endangered surrogate species, the `Oma`o; techniques that are now being used for recovery of the endangered Puaiohi. In 1995 and 1996, 29 viable `Oma`o eggs were collected from the wild. Of 27 chicks hatched, 25 were hand‐reared and released into Pu`u Wa`awa`a Wildlife Reserve. Using the techniques developed for the `Oma`o, a captive propagation and release program was initiated in 1996 to aid the recovery of the endangered Puaiohi. Fifteen viable Puaiohi eggs were collected from the wild (1996–1997) to establish a captive breeding flock to produce birds for re‐introduction. These Puaiohi reproduced for the first time in captivity in 1998 (total Puaiohi chicks reared in captivity 1996–1998 = 41). In 1999, 14 captive‐bred Puaiohi were re‐introduced into the Alaka`i Swamp, Kaua`i. These captive‐bred birds reproduced and fledged seven chicks in the wild after release. This is the first endangered passerine recovery program using this broad spectrum of management techniques (collection of wild eggs, artificial incubation, hand‐rearing, captive‐breeding, and release) in which re‐introduced birds survived and bred in the wild. Long‐term population monitoring will be published separately [BRD, in preparation]. Zoo Biol 19:263–277, 2000. © 2000 Wiley‐Liss, Inc.     

Klinefelter's syndrome as a model of anomalous cerebral laterality: Testing gene dosage in the X chromosome pseudoautosomal region using a DNA microarray

Consistent handedness and language laterality are two of the most striking behavioral and cognitive asymmetries observed in humans. Alterations in the typical pattern of cerebral laterality, termed “anomalous dominance,” is observed in left-handers and some patients with verbal learning disabilities. We undertook the study of a genetically distinct group of subjects, XXY males (Klinefelter's syndrome; KS), who demonstrate anomalous dominance in a variety of testing paradigms in order to begin to elucidate the molecular basis of anomalous dominance in this population. KS subjects manifest specific verbal learning disability, evidence of altered functional laterality for phonologic processing, and an increase in left-handedness when measured by skill. It is proposed that an alteration in gene dosage in the pseudoautosomal region (PAR) of the sex chromosomes is the most likely explanation for anomalous dominance in these patients. This is especially intriguing in light of previously described genetic models of cerebral laterality that suggest a contributing locus in the PAR, or adjacent high homology regions of the X chromosome. We have developed an ordered DNA microarray covering the X chromosome PAR at high resolution for hybridization with two-color fluorescently labeled probes. We demonstrate the ability to detect changes in hybridization signal that will facilitate efficient large-scale screening of this region for alterations in gene dosage associated with features of anomalous dominance and other cognitive or behavioral phenotypes. Dev. Genet. 23:215–229, 1998. © 1998 Wiley-Liss, Inc.     

Protein folding mechanisms and the multidimensional folding funnel

An important idea that emerges from the energy landscape theory of protein folding is that subtle global features of the protein landscape can profoundly affect the apparent mechanism of folding. The relationship between various characteristic temperatures in the phase diagrams and landmarks in the folding funnel at fixed temperatures can be used to classify different folding behaviors. The one-dimensional picture of a folding funnel classifies folding kinetics into four basic scenarios, depending on the relative location of the thermodynamic barrier and the glass transition as a function of a single-order parameter. However, the folding mechanism may not always be quantitatively described by a single-order parameter. Several other order parameters, such as degree of secondary structure formation, collapse and topological order, are needed to establish the connection between minimalist models and proteins in the laboratory. In this article we describe a simple multidimensional funnel based on two-order parameters that measure the degree of collapse and topological order. The appearance of several different “mechanisms” is illustrated by analyzing lattice models with different potentials and sequences with different degrees of design. In most cases, the two-dimensional analysis leads to a classification of mechanisms totally in keeping with the one-dimensional scheme, but a topologically distinct scenario of fast folding with traps also emerges. The nature of traps depends on the relative location of the glass transition surface and the thermodynamic barrier in the multidimensional funnel. Proteins 32:136–158, 1998. © 1998 Wiley-Liss, Inc.     

Kinetochore-bound Mps1 regulates kinetochore–microtubule attachments via Ndc80 phosphorylation

Dividing cells detect and correct erroneous kinetochore–microtubule attachments during mitosis, thereby avoiding chromosome missegregation. The Aurora B kinase phosphorylates microtubule-binding elements specifically at incorrectly attached kinetochores, promoting their release and providing another chance for proper attachments to form. However, growing evidence suggests that the Mps1 kinase is also required for error correction. Here we directly examine how Mps1 activity affects kinetochore–microtubule attachments using a reconstitution-based approach that allows us to separate its effects from Aurora B activity. When endogenous Mps1 that copurifies with kinetochores is activated in vitro, it weakens their attachments to microtubules via phosphorylation of Ndc80, a major microtubule-binding protein. This phosphorylation contributes to error correction because phospho-deficient Ndc80 mutants exhibit genetic interactions and segregation defects when combined with mutants in other error correction pathways. In addition, Mps1 phosphorylation of Ndc80 is stimulated on kinetochores lacking tension. These data suggest that Mps1 provides an additional mechanism for correcting erroneous kinetochore–microtubule attachments, complementing the well-known activity of Aurora B.     

Differential regulation of endogenous cadherin expression in Madin-Darby canine kidney cells by cell-cell adhesion and activation of beta -catenin signaling

Cadherins mediate cell-cell adhesion, but little is known about how their expression is regulated. In Madin-Darby canine kidney (MDCK) cells, the cadherin-associated cytoplasmic proteins alpha- and beta-catenin form high molecular weight protein complexes with two glycoproteins (Stewart, D. B., and Nelson, W. J. (1997) J. Biol. Chem. 272, 29652-29662), one of which is E-cadherin and the other we show here is the type II cadherin, cadherin-6 (K-cadherin). In low density, motile MDCK cells, the steady-state level of cadherin-6 is low, but protein is synthesized. However, following cell-cell adhesion, cadherin-6 becomes stabilized and accumulates by >50-fold at cell-cell contacts while the E-cadherin level increases only 5-fold during the same period. To investigate a role of beta-catenin in regulation of cadherin expression in MDCK cells, we examined the effects of expressing signaling-active beta-catenin mutants (DeltaGSK, DeltaN90, and DeltaN131). In these cells, while levels of E-cadherin, alpha- and beta-catenin are similar to those in control cells, levels of cadherin-6 are significantly reduced due to rapid degradation of newly synthesized protein. Additionally, these cells appeared more motile and less cohesive, as expression of DeltaGSK-beta-catenin delayed the establishment of tight confluent cell monolayers compared with control cells. These results indicate that the level of cadherin-6, but not that of E-cadherin, is strictly regulated post-translationally in response to Wnt signaling, and that E-cadherin and cadherin-6 may contribute different properties to cell-cell adhesion and the epithelial phenotype.