Agouti Protein Inhibits the Production of Eumelanin and Phaeomelanin in the Presence and Absence of α-Melanocyte Stimulating Hormone

Melanocytes synthesise two types of melanin: the brown-black eumelanin and the red-yellow phaeomelanin. In mice, the relative proportions of these two melanins are regulated by α-MSH, which preferentially increases the synthesis of eumelanin and by the Agouti protein (AP), the expression of which correlates with the growth of yellow phaeomelanin-containing hair. It has been proposed that AP acts by antagonizing the action of α-MSH at the MCI receptor, although it has been suggested that it may also act independently of α-MSH. In the present study we show that AP inhibits melanogenesis in B16F1 melanoma cells in the presence and absence of α-MSH and also causes dose-related decreases in the synthesis of both eumelanin and phaeomelanin. In the presence of α-MSH AP had a greater effect on eumelanin production and this is consistent with an antagonistic action at the MCI receptor. In the absence of α-MSH however, AP produced similar reductions in the synthesis of both melanins. These changes were not seen in B16G4F cells which lack the MCI receptor, suggesting that even in the absence of α-MSH AP acts at the MCI receptor. How this action is mediated at the intracellular level is not yet clear, although it appears to be associated with a decrease in tyrosinase activity.     

Effect of Actinomycin D and Cycloheximide on Gonadotropin-Induced 17α, 20β-Dihydroxy-4-pregnen-3-one Production by Intact Ovarian Follicles and Granulosa Cells of the Amago Salmon,Oncorhynchus rhodurus*

The effect of actinomycin D and cycloheximide on gonadotropin (partially purified chum salmon gonadotropin, SGA)-induced 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-diOHprog, a maturation-inducing steroid in amago salmon) production was examined in intact ovarian follicles and granulosa cells of postvitellogenic amago salmon, Oncorhynchus rhodurus. Both actinomycin D and cycloheximide blocked gonadotropin-induced 17α, 20β-diOHprog production by intact follicles. In contrast, gonadotropin-induced 17α-hydroxyprogesterone production by intact follicles was not abolished by actinomycin D, but was abolished by cycloheximide, suggesting that postvitellogenic amago salmon ovarian follicles already contain the RNAs necessary for the synthesis of 17α-hydroxyprogesterone. In isolated granulosa cells, chum salmon gonadotropin was able to stimulate 17α, 20β-diOHprog production only when a precursor, 17α-hydroxyprogesterone was provided in the incubation medium, indicating that gonadotropin acts directly on granulosa cells to enhance the activity of 20β-hydroxysteroid dehyrogenase (20β-HSD). Total inhibition of 20β-HSD enhancement in granulosa cells, judged by 17α, 20β-diOHprog production, was achieved when actinomycin D was added between 1 hr before the start of incubation with 17α-hydroxyprogesterone and gonadotropin to 6 hr after. With cycloheximide total inhibition was observed when added in the period of 1 hr before to 9 hr after the start of the incubation. These results suggest that chum salmon gonadotropin acts on granulosa cells to enhance the de novo synthesis of 20β-HSD by a mechanism involving RNA synthesis.     

Production and properties of monoclonal antibodies to Solanum nodiflorum mottle sobemovirus

Black raspberry necrosis virus (BRNV) reaches only very low concentrations in herbaceous plants and is difficult to maintain in culture. However, in a mixed culture with an unrelated virus, Solanum nodiflorum mottle (SNMV), in the genus Sobemovirus, the concentration of BRNV particles increases about 1000‐fold. In attempts to produce monoclonal antibodies (MAbs) to BRNV for diagnostic use, purified virus particles from the mixed virus culture were used as immunogen and the resultant antibodies screened against cultures of SNMV alone, BRNV+SNMV and healthy plant extracts. None of the virus‐specific MAbs obtained in this way was specific to BRNV but six were specific to SNMV. Although the original objective was not achieved, the SNMV MAbs were characterised and used to study serological properties of SNMV and other Sobemoviruses. Characterisation of the six SNMV MAbs showed that four were IgG3, one IgG1 and the other IgG2b. SNMV was detected by all six MAbs in ELISA, by five in Western blotting, by three in agarose gel double diffusion tests, but only one was suitable for trapping virus particles in immuno‐electron microscopy (IEM). In Western blotting using virus in sap extracts of Nicotiana clevelandii, each of the five MAbs detected a single major band of Mc. 31 000 in sap containing SNMV, and additional bands of lower mass attributed to degradation of coat protein. In various serological tests, no cross‐reactions were detected between SNMV and seven other viruses from the genus Sobemovirus. However, in IEM but not in Western blotting, significant cross‐reactions were observed between SNMV and Velvet tobacco mottle virus, another species from the genus Sobemovirus. The significance of these different findings is discussed.     

Sensory capacities and the nocturnal habit of owls (Strigiformes)

Behavioural studies show that in the eye of the Tawny Owl Strix aluco both absolute visual sensitivity and maximum spatial resolution at low light levels are close to the theoretical limit dictated principally by the quantal nature of light and the physiological limitations on the structure of vertebrate eyes. However, when the owl's visual sensitivity in relation to naturally occurring ligh levels is analysed, it is concluded that at night there will often be occasions when vision can only be used to control the owl's behaviour with respect to large objects.
Owls are capable of detecting and catching prey by hearing alone. However, absolute auditory sensitivity is not superior to that of mammals (including Man), but does appear to have reached the absolute limit on sensitivity in the aerial environment, which is dictated by the minimum ambient sound level.
An explanation of the owl's ability to be active at night based only upon high sensory sensitivity is thus untenable. Many features of the natural behaviour of the Tawny Owl (e.g., the high degree of territoriality, prey catching technique, dietary spectrum) may be interpreted as reflections of an additional requirement for the nocturnal habit beyond high sensory sensitivity: detailed knowledge of local topography.     

The evolution of thunniform locomotion and heat conservation in scombrid fishes: New insights based on the morphology of Allothunnus fallai

Two significant functional differences–a more anterior and internally positioned red myo‐tomal muscle mass and modification of the red‐muscle vascular supply to form counter‐current heat exchangers–distinguish the tunas (tribe Thunnini) from other species in the teleost family Scombridae. Neither of these characteristics is found in the bonitos (tribe Sardini), the sister group to the Thunnini. The most recent scombrid classification places the slender tuna, Allothunnus fallai, in the tribe Sardini, but some earlier studies suggested that this species should be a member of the Thunnini. Allothunnus fallai does not possess the lateral subcutaneous arteries and veins or the lateral heat‐exchanging retia typical of tunas. However, we have found that this species has a highly modified central circulation (dorsal aorta, post cardinal vein, and associated branch vessels) similar to the central heat‐exchanging retia of certain tunas, an enlarged haemal arch to accommodate this structure, and the anterior, internal placement of red muscle characteristic of tunas. With these new characters, phylogenetic reconstructions based on parsimony place A. fallai as the sister taxon to the tunas, establish that it is the most basal tuna species, and support the hypothesis that the derivation of tunas from a bonito‐like ancestor occurred through selection for an integrated set of characteristics affecting locomotion and endothermy. The major features of this hypothesis are as follows. (1) Selection for continuous, steady, and efficient swimming resulted in changes in body shape (the result of enlargement of the anterior myotomes, the anterior and internal shift of red muscle, and a narrowing of the caudal peduncle) which increased streamlining and led to the adoption of the thunniform swimming mode unique to the tunas. (2) Alterations in blood supply necessitated by the anterior shift in red muscle led to the interdigitation of numerous arterial and venous branches which set the stage for heat conservation. (3) The evolution of endothermy, together with thunniform swimming, contributed significantly to the ecological radiation and diversification of tunas during the Early Tertiary Period. Our studies of A fall thus suggest that the shift in red muscle position and changes in central circulation preerded the evolution of red‐muscle endothermy. Co‐evolutionary changes in red muscle quantity and distribution and in vascular specializations for heat conservation have led to different macroevolutionary trajectories among the now five genera and 14 tuna species of tunas and appear to reflect the influence of changing paleocological and paleoccanographic conditions, including cooling, that occurred in the Tertiary     

The Arcoidea (Mollusca: Bivalvia): a review of the current phenetic-based systematics

The diversity and adaptive radiations of modern Arcoidea, here considered to contain the families Arcidae, Noetiidae, Cucullaeidae, and Glycymerididae, are reviewed. Most fall into either epibyssate or endobyssate life habits with only the Glycymerididae living as free burrowers. The phenetic characters of the families within the Arcoida are reviewed and the families are shown to be supported by very few synapomorphic characters. Homoplasy is shown to be widespread and is illustrated in a series of discussions on the ligament, epibyssate–endobyssate radiations, and possible parallelism within genera, and in a review of arcoid anatomical characters. Previously published molecular data are reviewed and these support the inclusion of the Glycymerididae in the Arcoidea. They also indicate, however, that polyphyly is probably widespread at the subfamily level.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 148 , 237–251.     

Biology of Rhoophilus loewi (Hymenoptera: Cynipoidea: Cynipidae), with implications for the evolution of inquilinism in gall wasps

The sole described indigenous afrotropical cynipid, the South African endemic Rhoophilus loewi , was originally described as a gall inducer. As predicted by phylogenetic relationships, we confirm that R. loewi is instead an inquiline wasp. Although all other cynipid inquilines develop in galls induced by cynipid wasps, or very rarely cecidomyiid midges, R. loewi is the only cynipid inquiline of a lepidopteran gall, inducing secondary inquiline cells in galls induced by a cecidosid moth genus Scyrotis on Rhus species (Anacardiaceae). Rhoophilus is a lethal inquiline; its larval cells expand into the hollow interior of the host gall resulting in death of the gall inducer. Rhoophilus loewi is redescribed and the final-instar larva described for the first time. We describe host-plant associations, the morphology and phenology of gall formation, and the suite of parasitoid Hymenoptera associated with these galls. The community centred on Scyrotis galls is compared with those observed in other hosts of inquiline cynipids. Elucidation of the life history of R. loewi has fundamental implications for understanding the evolution of cynipid wasps.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 153–172.     

The soil seed bank of Triodia basedowii in relation to time since fire

Triodia basedowii seeds were found almost exclusively within Triodia hummocks, both in the centres and under the edges. Averaged over the whole ground surface, live seed densities in soil and litter were 85-263 m^?2 in stands which had been burnt 9 and > 35 years previously. These live seeds comprised only 56% of all filled grains, and in turn filled grains were present in only about 6% of all fruits. Thus > 4% of fruits contained live seeds. A site burnt 1 year previously had about 35 live seeds m^?2 still ungerminated, but at sites burnt 3 years previously none of the pre-fire seed bank was alive. After fire, juvenile plants were found predominantly around the edges of where hummocks had been before the fire, suggesting that seeds survive fires better around the edges.     

Relationships in consultation

The cause of medicine is advanced by the proper exchange of services between general practitioners and specialists. As a medical group and singly, physicians stand to benefit by strengthening their relationships; and the one to benefit most of all by this combination of services is the patient. Any physician of integrity admits that it is impossible for one physician to know all there is to know about every medical subject. The establishment of rules of conduct to be followed by those who get together to solve a medical problem will promote the use of advisory practice.