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Melanocytes originate from the neural crest in vertebrates and migrate to the body surface where they differentiate into functional cells. Genes involved in melanocyte differentiation can be classified into two groups. One of them consists of the functional genes that control proteins specific to the function of the melanocyte. As the representative gene of this category, albino (c) locus in the mouse is considered to control tyrosinase, the key enzyme in melanogenesis. cDNA for mouse tyrosinase has been cloned and sequenced. The cDNA can be used to detect tyrosinase mRNA synthesized during melanocyte differentiation. On the other hand, genes such as brown (b) or pink-eyed dilution (p) have been assumed to control melanosome proteins. The other category consists of genes that regulate the expression of these functional genes directly or indirectly. In the mouse, so-called white-spotting genes and genes of the agouti series are considered to fall into this category. Based on the fact that mutations at the white-spotting loci result in the absence of melanocytes in a particular area of skin, it is assumed that some of these loci control the factors that promote either differentiation or migration of melanoblasts and are candidates for the classic regulator genes Genes at the agouti (a) locus in the mouse determine the type of melanin synthesized in hair follicle melanocytes, that is eumelanin or pheomelanin. An interesting feature of this locus is that the site of gene action is not within the melanocytes but in the cells surrounding them. The results of our study indicate that the gene product of the a-locus interacts with α-MSH at the α-MSH receptor site, regulates the cellular cAMP level via a signal transduction system and, in turn, determines the type of melanin synthesized in the cells. 相似文献
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KAZUNORI YAMAHIRA TAKESHI NISHIDA † AISAKU ARAKAWA ‡ HIROAKI IWAISAKI ‡ 《Biological journal of the Linnean Society. Linnean Society of London》2009,96(4):867-874
Variation in the number of abdominal vs. caudal vertebrae is an important source of morphological diversification of fish. It is not clear, however, whether abdominal and caudal regions evolve independently. Regressions of offspring on parents demonstrated substantial additive genetic variation within populations, i.e. heritability, in both abdominal and caudal vertebral numbers of the medaka ( Oryzias latipes ). However, the heritability of caudal vertebrae tended to be smaller than that of abdominal vertebrae in some estimations, suggesting that abdominal and caudal regions are controlled by separate developmental modules. Furthermore, genetic correlation between abdominal and caudal vertebral numbers, estimated using full-sib family means, was negative but weak, supporting independent evolution. In addition, substantial genetic differentiation among populations was demonstrated in abdominal vertebral numbers, but not in caudal numbers. These results support our view that Jordan's rule, a geographical tendency for fish from higher latitudes to have more vertebrae, in this fish reflects local adaptations of abdominal vertebral numbers. In contrast, the low heritability of caudal vertebrae may reflect the intrinsic invariability of genes associated with a change in caudal vertebral numbers. This genetic constraint may have restricted morphological diversification of not only the medaka, but also the Order Beloniformes as a whole. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 867–874. 相似文献
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MIYUKI YAMANAKA SHIRO KOBAYASHI HIROAKI SETOGUCHI 《Botanical journal of the Linnean Society. Linnean Society of London》2008,157(3):501-518
The geographical distribution of chloroplast DNA (cpDNA) haplotypes and nuclear ribosomal internal transcribed spacer (nrITS) genotypes of Japanese Corylopsis (Hamamelidaceae), which consists of four species, was investigated. Two hundred and five individuals belonging to four species from 30 populations, covering the entire geographical range, were studied. Based on approximately 1108 bp of the three non-coding regions of cpDNA, nine haplotypes were detected, and each was distinguished from adjacent haplotypes by one substitution. Based on approximately 507-bp nrITS sequences, 47 genotypes were detected, for which three clades were identified in the phylogenetic analysis. There was inconsistency between the cpDNA haplotypes, nrITS genotypes, and classification of Corylopsis taxa, possibly because of incomplete lineage sorting or introgressive hybridization. The distribution of the haplotypes was highly structured geographically, and N ST (0.893) was significantly greater than G ST (0.819), implying that the current distribution of Corylopsis species was structured phylogeographically during Quaternary climatic oscillations. The haplotype composition and results of analysis of molecular variance showed that the populations in Hokuriku were highly divergent, suggesting that they are long-term persistent populations arising from refugia during the Quaternary climatic oscillations. Refugial populations in Chugoku and Shikoku may have lost genetic diversity because of a bottleneck resulting from a small population size, followed by post-glacial range expansion. Pre-existing refugia may have been so small that the subsequent range expansion replaced the pre-existing genetic structure. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 501–518. 相似文献
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Abstract: Stegodon protoaurorae sp. nov. (Proboscidea) from the lower Pleistocene Terada Formation of the Kazusa Group in Japan is proposed as a new species based on characteristic features of plate formula, molar size, tooth enamel and plate frequency, and is described herein. The specimen of the new species was transported by autumn storms and buried. The new species fills an evolutionary gap between S. miensis and S. aurorae. Speciation in the lineage from S. miensis through S. protoaurorae to S. aurorae is inferred to have been caused by reduction of terrestrial space during marine transgression. The biostratigraphic distribution of S. protoaurorae suggests intercalation of a new S. protoaurorae Zone between the S. miensis Zone and the S. aurorae Zone. The S. protoaurorae Zone can be defined in the Nakatsu Group and the Terada Formation of the Kazusa Group, and can be assigned an age of 2.9–2.1 Ma. 相似文献
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HIROAKI SHIOTA MASAHITO T. KIMURA 《Biological journal of the Linnean Society. Linnean Society of London》2007,90(2):375-380
Cold-tolerant ectothermal animals are generally absent from warmer regions, suggesting that the acquisition of cold tolerance is associated with the loss of adaptation to warmer environments. In the present study, we compared thermal tolerance, walking speed (WS) and pupal development (PD) for 28 drosophilid species from cool-temperate, warm-temperate, and subtropical regions by the phylogenetically-based method and the conventional regression to understand trade-offs between these traits. A significant negative relationship was observed between cold tolerance and the rate of PD in both sexes and between cold tolerance and WS in the male in the phylogenetically-based analysis. Similar results were obtained in the conventional regression analysis, although the level of significance somewhat differed. Thus, cold tolerant species are assumed to have lost abilities to develop and walk fast. Subsequently, they may become more vulnerable to predators, parasitoids or infectious microorganisms and may have become extinct in warmer regions through enemy-mediated interactions and/or resource competition with cold susceptible species with faster development and quicker locomotion. In the present study, no significant relationship was observed between heat tolerance and WS or the rate of PD in the phylogenetically-based analysis, although heat tolerance was significantly related with the rate of PD in the conventional regression analysis. Thus, trade-offs associated with heat tolerance were not apparent. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 375–380. 相似文献
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TOSHIHIRO YOSHIHARA NOBUO SUZUI SATOMI ISHII MAYU KITAZAKI HARUAKI YAMAZAKI KAZUYOSHI KITAZAKI NAOKI KAWACHI YONG‐GEN YIN SAYURI ITO‐TANABATA SHIN‐NOSUKE HASHIDA KAZUHIRO SHOJI HIROAKI SHIMADA FUMIYUKI GOTO SHU FUJIMAKI 《Plant, cell & environment》2014,37(5):1086-1096
Cadmium (Cd) accumulations in a Cd hyper‐accumulator fern, Athyrium yokoscense (Ay), and tobacco, Nicotiana tabacum (Nt), were kinetically analysed using the positron‐emitting tracer imaging system under two medium conditions (basal and no‐nutrient). In Ay, maximumly 50% and 15% of the total Cd accumulated in the distal roots and the shoots under the basal condition, respectively. Interestingly, a portion of the Cd in the distal roots returned to the medium. In comparison with Ay, a little fewer Cd accumulations in the distal roots and clearly higher Cd migration to the shoots were observed in Nt under the basal condition (maximumly 40% and 70% of the total Cd, respectively). The no‐nutrient condition down‐regulated the Cd migration in both species, although the regulation was highly stricter in Ay than in Nt (almost no migration in Ay and around 20% migration in Nt). In addition, the present work enabled to estimate physical and physiological Cd accumulation capacities in the distal roots, and demonstrated condition‐dependent changes especially in Ay. These results clearly suggested occurrences of species‐/condition‐specific regulations in each observed parts. It is probable that integration of these properties govern the specific Cd tolerance/accumulation in Ay and Nt. 相似文献
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JOSHUA B. FISHER YADVINDER MALHI DAMIEN BONAL HUMBERTO R. DA ROCHA ALESSANDRO C. DE ARAÚJO MINORU GAMO MICHAEL L. GOULDEN TAKASHI HIRANO ALFREDO R. HUETE HIROAKI KONDO TOMO'OMI KUMAGAI HENRY W. LOESCHER SCOTT MILLER ANTONIO D. NOBRE YANN NOUVELLON STEVEN F. OBERBAUER SAMREONG PANUTHAI OLIVIER ROUPSARD SCOTT SALESKA KATSUNORI TANAKA NOBUAKI TANAKA KEVIN P. TU CELSO VON RANDOW 《Global Change Biology》2009,15(11):2694-2714
Tropical vegetation is a major source of global land surface evapotranspiration, and can thus play a major role in global hydrological cycles and global atmospheric circulation. Accurate prediction of tropical evapotranspiration is critical to our understanding of these processes under changing climate. We examined the controls on evapotranspiration in tropical vegetation at 21 pan-tropical eddy covariance sites, conducted a comprehensive and systematic evaluation of 13 evapotranspiration models at these sites, and assessed the ability to scale up model estimates of evapotranspiration for the test region of Amazonia. Net radiation was the strongest determinant of evapotranspiration (mean evaporative fraction was 0.72) and explained 87% of the variance in monthly evapotranspiration across the sites. Vapor pressure deficit was the strongest residual predictor (14%), followed by normalized difference vegetation index (9%), precipitation (6%) and wind speed (4%). The radiation-based evapotranspiration models performed best overall for three reasons: (1) the vegetation was largely decoupled from atmospheric turbulent transfer (calculated from Ω decoupling factor), especially at the wetter sites; (2) the resistance-based models were hindered by difficulty in consistently characterizing canopy (and stomatal) resistance in the highly diverse vegetation; (3) the temperature-based models inadequately captured the variability in tropical evapotranspiration. We evaluated the potential to predict regional evapotranspiration for one test region: Amazonia. We estimated an Amazonia-wide evapotranspiration of 1370 mm yr−1 , but this value is dependent on assumptions about energy balance closure for the tropical eddy covariance sites; a lower value (1096 mm yr−1 ) is considered in discussion on the use of flux data to validate and interpolate models. 相似文献