Molecular Characterization of the Mouse Tyrosinase Gene:Pigment Cell-Specific Expression in Transgenic Mice

Tyrosinase is the key enzyme in melanin synthesis, and is expressed in the pigment epithelium of the retina, a cell layer derived from the optic cup; and in neural crest-derived melanocytes of skin, hair follicle, choroid, and iris. The tyrosinase gene has been cloned and shown to map to the well-characterized c-locus (albino locus) of the mouse. Subsequent studies demonstrated that a functional tyrosinase minigene was able to rescue the albino phenotype in transgenic mice. The transgene was expressed in a cell type-specific manner in skin and eye. During development of the mouse, the tyrosinase gene is expressed in the pigment epithelium of the retina as early as day 10.5 of gestation. In the hair follicle, tyrosinase gene expression is detected from day 16.5 onwards. This cell-type–specific expression is largely reproduced in transgenic mice. Our results suggest that sequences in the immediate vicinity of the mouse tyrosinase gene are sufficient to provide cell type-specificity and developmental regulation in melanocytes and the pigment epithelium.     

Freeze-Fracture Study of Malaria Sporozoites: Antibody-Induced Changes of the Pellicular Membrane*

Plasmodium cynomolgi, Plasmodium knowlesi, and Plasmodium berghei sporozoites, before and after incubation with immune serum, were studied after freeze-fracture by electron microscopy. There were evenly distributed numerous intramembranous particles (IMP) on the P face of the outer membrane. The E face of the plasma membrane had fewer IMP than its P face. The E face of the intermediate membrane had few IMP and also linear arrays of slightly raised ridges running the length of the parasite. The P face of the intermediate membrane had many IMP aligned along the long axis of the sporozoite. On the P face of the inner membrane. IMP were arranged in very distinct rows conforming to the long axis of the parasite; the E face of this membrane had a few randomly distributed IMP. A prominent change in the sporozoite incubated in immune serum was the appearance of a layer of aggregated particles around the parasite. The P face of the plasma membrane had several clear areas devoid of IMP and IMP aggregates. No changes were seen in the other fractured faces of the pellicle. These observations suggest that immune serum acts only on the P face of the plasma membrane.     

Fat, Energy and Mammalian Survival

Adipose tissue plays a critical role in mammalian life historystrategies, serving as an organ for the storage of food andenergy, as a source of heat and water and as thermal insulation.The food and energy storage roles are especially important inallowing the animals to survive food shortages and stressesassociated with competition for mates, territorial defense,gestation and lactation, and to accomplish migrations. The composition,cellularity and anatomical site of adipose depots in a mammalcan influence both the amount of fat stored and its availabilityand usefulness in any given situation. The fatty acids and complexlipids in adipose tissue, blood vessels, nerves and brain changein response to ambient temperature and the low body temperaturesduring hibernation. Early nutrition may influence the numberof fat cells developed by a mammal, and thus affect its abilityto survive adversity. Desert species develop localized depotswhich will not interfere with temperature regulation, whileanimals in cold environments use their extensive superficialfat layers as insulation.     

The Physiological Mechanisms of Acclimatization in Tropical Reef Corals

SYNOPSIS. The ability of scleractinian corals to survive changesthat are predicted in the global environment over the next centurywill lie in their physiological mechanisms of acclimatization.Corals display rapid modifications in behavior, morphology andphysiology enabling them to photoacclimate to changing lightconditions, a scenario that demonstrates considerable biologicalflexibility. Here we argue that the acclimatization mechanismsin corals are fundamentally similar to those exhibited by otherinvertebrate taxa. We discuss protein metabolism as a mechanismunderlying acclimatization responses in reef corals, and explorethe relationship between protein turnover, metabolic rate, growthrate, and acclimatization capacity. Our preliminary analysessuggest that corals with low growth rates (µCa/mgN/h)and high metabolic rates (µO₂/cm²/hr), such as the massivespecies, acclimatize more effectively than those with high growthrates and low metabolic rates, a feature that is characteristicof branching species. We conclude that studies of protein turnover,combined with temporally relevant investigations into the dynamicaspects of coral dinoflagellate symbioses will provide considerableinsight into why corals exhibit such a high level of variationin response to the same environmental challenge. Furthermore,a more detailed understanding of acclimatization mechanismsis essential if we are to predict how a coral assemblage willrespond to present and future environmental challenges.     

Twelve polymorphic microsatellite loci from the Asian citrus psyllid,Diaphorina citri Kuwayama,the vector for citrus greening disease,huanglongbing

Twelve polymorphic microsatellite markers were developed from microsatellite‐enriched DNA libraries and mined from an expressed sequence tags library of Diaphorina citri, the vector of the citrus greening disease (huanglongbing). Analysis of 288 individuals from Florida, Texas, and Brazil showed that allelic diversity ranged from three to eight alleles per locus and observed and expected heterozygosities ranged from 0.014 to 0.569 and from 0.052 to 0.653, respectively. These variable microsatellite loci can provide means for assessing overall genetic variation and migration patterns for this agriculturally important pest species. This information can be used to aid in developing successful management strategies.     

Coat colour variation in the banded palm civet Hemigalus derbyanus and in Owston's civet Chrotogale owstoni

1. Coat colour variation was studied in two viverrid species belonging to the subfamily Hemigalinae, on the basis of museum specimens and observations of live animals. 2. In both species, polymorphism and ontogenetic colour change occur, and in the Owston's civet, sexual dimorphism in coat colour was identified.     

Back to the future: using palaeolimnology to infer long‐term changes in shallow lake food webs

1. Shallow lakes are often cited as classic examples of systems that exhibit trophic cascades but, whilst they provide good model systems with which to test general ecological theory and to assess long‐term community change, their food web linkages have rarely been resolved, so changes associated with the structure and dynamics of the ecological network as a whole are still poorly understood. 2. We sought to redress this, and to demonstrate the potential benefits of integrating palaeolimnological and contemporary data, by constructing highly resolved food webs and stable isotope derived measures of trophic interactions and niche space, for the extant communities of two shallow U.K. lakes from different positions along a gradient of eutrophication. The contemporary surface sediment cladoceran and submerged macrophyte assemblages in the less enriched site, Selbrigg Pond, matched the palaeolimnological assemblages of the more enriched site, Felbrigg Hall Lake, in its more pristine state during the 1920s. Thus, Selbrigg was a temporal analogue for Felbrigg, from which the consequences of long‐term eutrophication on food web structure could be inferred. These data represent the first steps towards reconstructing not only past assemblages (i.e. nodes within a food web), but also past interactions (i.e. links within a food web): a significant departure from much of the previous research in palaeolimnology. 3. The more eutrophic food web had far fewer nodes and links, and thus a less reticulate network, than was the case for the more pristine system. In isotopic terms, there was vertical compression in δ¹⁵N range (NR) and subsequent increased overlap in isotopic niche space, indicating increased trophic redundancy within Felbrigg. This structural change, which was associated with a greater channelling of energy through a smaller number of nodes as alternative feeding pathways disappear, could lead to reduced dynamic stability, pushing the network towards further simplification. These changes reflected a general shift from a benthic‐dominated towards a more pelagic system, as the plant‐associated subweb eroded. 4. Although these data are among the first of their kind, the palaeo‐analogue approach used here demonstrates the huge potential for applying food web theory to understand how and why these ecological networks change during eutrophication. Furthermore, because of the rich biological record preserved in their sediments, shallow lakes represent potentially important models for examining long‐term intergenerational dynamics, thereby providing a means by which models and data can be integrated on meaningful timescales – a goal that has long proved elusive in food web ecology.