シマホルトノキにおける生育環境に対応した遺伝構造とその維持要因の解明

Ecological speciation on an oceanic island is a well-known evolutionary phenomenon. In ecological speciation, diversification via the evolution of barriers to gene flow between populations occurs as a result of divergent natural selection under different environmental conditions. The Bonin (Ogasawara) Islands, a typical oceanic island group in the northwestern Pacific Ocean, are located approximately 1,000 km south of mainland Japan. In this study, I investigated Elaeocarpus photiniifolia, an endemic tree species in the Bonin Islands. This species grows in different vegetation types even within a single island, including dry scrubs and mesic forests, although no morphological differentiation has been reported. Therefore, I considered two hypotheses: first, that E. photiniifolia forms a large, randomly mating population on each island and adapts to its different habitats by means of phenotypic plasticity; and second, that E. photiniifolia is differentiated into genetically distinct groups associated with different habitats within an island and exhibits assortative mating within respective habitats. The detection of significant genetic differentiation associated with different habitats would suggest that E. photiniifolia is undergoing ecological speciation. Elaeocarpus photiniifolia is also important to the conservation of a critically endangered endemic subspecies of Japanese wood-pigeon, Columba janthina nitens. This bird species feeds on the fallen seeds of E. photiniifolia. Therefore, to maintain the population of C. janthina nitens, an E. photiniifolia propagation project that includes restoration plantings is being conducted in the Bonin Islands. To minimize the genetic disturbance resulting from restoration planting, it is necessary to elucidate the genetic structure of E. photiniifolia. To facilitate population genetic studies, I first developed nuclear microsatellite markers from expressed sequence tags (EST-SSRs) for E. photiniifolia. I constructed a complementary DNA (cDNA) library by de novo pyrosequencing of total RNA extracted from a seedling. I then designed 267 primer pairs from the EST library. Of the 48 tested loci, 25 were polymorphic among 41 individuals representing the entire geographical range of the species, with the number of alleles per locus and expected heterozygosity ranging from 2 to 14 and from 0.09 to 0.86, respectively. Most loci were transferable to a related species, Elaeocarpus sylvestris. These markers can be used to evaluate the genetic structure of E. photiniifolia and related species. Then, I examined the genotypes of 639 individuals from 19 populations of E. photiniifolia and compared this species to its close relative E. sylvestris at 24 EST-SSRs. These data revealed clear genetic differentiation (1) between E. photiniifolia and E. sylvestris (0.307 ≤ FST ≤ 0.470) and (2) between the E. photiniifolia populations of the Chichijima and Hahajima Island Groups within the Bonin Islands (0.033 ≤ FST ≤ 0.121). The results also showed (3) genetic differentiation between E. photiniifolia populations associated with dry scrubs and mesic forests in the Chichijima Island Group (0.005 ≤ FST ≤ 0.071). Furthermore, it was shown that isolation by distance was not responsible for genetic differentiation. This result also supported the occurrence of genetic structure associated with habitat variation. Moreover, I observed the flowering phenology of E. photiniifolia on Chichijima Island to clarify possible pre-mating isolation mechanisms. I also investigated the environmental conditions in dry scrubs and mesic forests, or the two habitat types where the species occurs, to find the environmental factors that may cause disruptive selection. The flowering phenology data indicated that the populations in the two habitat types are reproductively isolated, with trees located in dry scrubs flowering before trees growing in mesic forests. The two habitats differed in environmental factors related to soil moisture content and vegetation height. These findings support the hypothesis that E. photiniifolia is undergoing ecological speciation associated with habitat differences between dry scrubs and mesic forests. Based on the results of these genetic analyses, seed sources from environments similar to that of the candidate site and from within the same island are likely to be the most appropriate seed sources for restoration. However, various vegetation types are distributed in a mosaic across the entire Bonin Islands. Evaluation of the adaptive differentiation associated with various types of environmental components should be made in the future.首都大学東京, 2013-05-02, 博士(理学）, 乙第76号首都大学東

A Microfluidic Sensing System with a Multichannel Surface Plasmon Resonance Chip: Damage-free Characterization of Cells by Pattern Recognition

The development of a versatile sensing strategy for the damage-free characterization of cultured cells is of great importance for both fundamental biological research and industrial applications. Here, we present a pattern-recognition-based cell-sensing approach using a multichannel surface plasmon resonance (SPR) chip. The chip, in which five cysteine derivatives with different structures are immobilized on Au films, is capable of generating five unique SPR sensorgrams for the cell-secreted molecules that are contained in cell culture media. An automatic statistical program was built to acquire kinetic parameters from the SPR sensorgrams and to select optimal parameters as “pattern information” for subsequent multivariate analysis. Our system rapidly (~ 10 min) provides the complex information by merely depositing a small amount of cell culture media (~ 25 µL) onto the chip, and the amount of information obtained is comparable to that furnished by a combination of conventional laborious biochemical assays. This non-invasive pattern-recognition-based cell-sensing approach could potentially be employed as a versatile tool for characterizing cells. </p

Id2 deletion attenuates Apc-deficient ileal tumor formation

The expression level of inhibitor of DNA binding 2 (Id2) is increased in colorectal carcinomas and is positively correlated with poor prognosis. However, the functional significance of Id2 in intestinal tumorigenesis has not been fully defined using genetic approaches. Here, we show that Id2 promotes ileal tumor initiation in Apc-deficient mice. Expression of Id2 was stimulated by Wnt signaling through the enhancer region of the Id2 promoter at the early stage of tumorigenesis in Apc+/Δ716 (ApcΔ716) mice. Genetic depletion of Id2 in ApcΔ716 mice caused ∼80% reduction in the number of ileal polyps, but had little effect on tumor size. Notably, the lack of Id2 increased the number of apoptotic cells in the normal crypt epithelium of the mice. Furthermore, DNA microarray analysis revealed that the expression level of Max dimerization protein 1 (Mxd1), known as a c-Myc antagonist, was specifically increased by Id2 deletion in the ileal intestinal epithelium of ApcΔ716 mice. In contrast, the protein level of c-Myc, but not the mRNA level, was decreased by loss of Id2 in these mice. These results indicate that loss of Id2 inhibits tumor initiation by up-regulation of Mxd1 and down-regulation of c-Myc in ApcΔ716 mice

Within-female sperm allocation—Males inseminate at three different female body sites according to female mating history in a squid

&lt;p&gt;Theory predicts that males should allocate their costly sperm according to future mate availability and focal female conditions, e.g. promiscuity and fecundity, to maximise lifetime reproductive success. Some squids show insemination site polymorphism within a female—males deposit sperm capsules at different female body locations. Whether the choice of insemination site is influenced by the sperm-storing status of the female remains untested. We studied the squid &lt;em&gt;Loliolus sumatrensis&lt;/em&gt; – the females possess three insemination sites: the buccal membrane (BM), basal left IV arm (ARM) and lateral head behind the left eye (EYE). Analysis of seasonal dynamics identified a set priority for the initial use of insemination sites as BM then ARM then EYE, whereas the maximum number of stored spermatangia was greater as EYE&gt;ARM&gt;BM. The maturity status of females was correlated with the pattern, but not number, of inseminations. We found multiple paternity at all sites and the same genotypes in spermatangia collected from all three sites, suggesting male squids allocate their sperm to multiple insemination sites during a single mating episode according to the status of female sperm-storage. This study uncovered unusual within-female sperm allocation – male mating behaviours were influenced by female mating history.&lt;/p&gt;&lt;p&gt;Funding provided by: Ministry of Education, Culture, Sports, Science and Technology&lt;br&gt;Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100001700&lt;br&gt;Award Number: 21K06333&lt;/p&gt;&lt;p&gt;Funding provided by: Ministry of Education, Culture, Sports, Science and Technology&lt;br&gt;Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100001700&lt;br&gt;Award Number: 21K19158&lt;/p&gt