Chordates consist of cephalochordates, urochordates, and vertebrates. They originated from a common ancestor(s) by evolving a novel type of tadpole-like larva characterized by a notochord and dorsal neural tube. Urochordata or Tunicata comprises three classes, Ascidiacea (ascidians), Thaliacea (salps), and Appendicularia (larvaceans); are extremely diverse in morphology, life history, and mode of reproduction; and may include either free-swimming or sessile adults. Recent molecular phylogenies support the notion that cephalochordates are basal among chordates, with urochordates the sister group to vertebrates. This revitalized evolutionary scenario compels us to explain how the huge variety of lifestyles of extant urochordates evolved from a cephalochordate-like ancestor. Here, an advanced filter-feeder hypothesis is presented, in which, although the taxonomic position of larvaceans is enigmatic, it is argued that among urochordates, free-living larvaceans are basal, while sessile ascidians are derived. Urochordates might have evolved their traits in response to strong evolutionary advantages as specialists of suspension filter feeding. Nevertheless, the molecular mechanisms involved in the formation of the notochord and several other organs in ascidian embryos are more comparable to those of vertebrates than cephalochordates. Thus, urochordates are close relatives to vertebrates.

The gene nanos is essential for germ cell development. Although its functions and expression have been investigated in the mouse, nanos genes have yet to be well characterized in other vertebrates. Based on similarity and a syntenic analysis of nanos, we have identified four different nanos in the genome of medaka (Oryzias latipes). nanos1 is duplicated in teleost fish genomes and named nanos1a and nanos1b. Of all medaka nanos, nanos3 is well conserved in terms of expression and synteny. In contrast to a previous study on mice, nanos2 expression was not detected in the gonads at early stages of sex differentiation; however, both oogonia and spermatogonia in adult gonads exhibit nanos2 expression. nanos1a and 1b are both expressed in the developing brain, consistent with the expression of nanos1 in mice. In the gonads, nanos1a is expressed in the somatic cells surrounding oocytes and spermatocytes, whereas expression of nanos1b is not detectable in the gonads by in-situ hybridization. These results suggest common and distinct functions of nanos genes among vertebrates.

Certain plastic morphological responses of animals induced across a range of environmental conditions may be adapted for effective locomotor performance. Larvae of the salamander, Hynobius retardatus, occasionally swim upward to the surface to breathe air because aquatic respiration alone is insufficient to meet their increasing respiratory requirements for growth. We hypothesized that H. retardatus larvae living in deep water would show an induced plastic response affecting locomotor structures, namely, a deeper tail, similar to that induced by predatory dragonfly larvae (Aeschna juncea), to improve their swimming performance. In this study, larval salamanders responded similarly to different cues (waterborne chemicals in a predatory environment and distance to the water's surface) by developing deeper tails. The similar modifications in tail shape presumably increase a larva's swimming performance, thereby improving its ability both to escape an attacking predator and to swim to the surface for air. The response in tail shape induced by the predatory environment was rapid, but was more gradual in larvae raised in deep water, suggesting that animals may quickly assess a dangerous environment and immediately respond, whereas assessment of an environment not requiring an immediate response for survival may be slower, accounting for the delayed response.

Sexually mature male bitterlings, Rhodeus ocellatus ocellatus, exhibit distinct nuptial color, whereas females maintain a body color similar to that of juveniles. In the present study, body color and chromatophores were compared between male and female bitterlings, and the effects of androgens on body color and chromatophore densities were examined in females to clarify the role of androgen in the development of nuptial coloration and chromatophores. Males showed green, blue, and red color in specific regions of their skin and red color on the dorsal and caudal fins; females showed a subdued silver body color. For chromatophores, small greenish-type iridophores were observed in the green color region in the skin of males, whereas females had large spindle-shaped silvery-type iridophores in corresponding regions. Many erythrophores were observed in males in blue and red color regions in the skin and red color regions in the fins, but females possessed xanthophores in corresponding regions. The melanophore density of the skin was not different between males and females, but the distribution of melanophores in the fins was different between them. Treatment with 11-ketotestosterone or methyltestosterone induced male-type nuptial coloration in the female skin and fins. The distribution of chromatophores in androgen-treated females was similar to that in sexually mature males: an increase in the number of greenish-type iridophores and erythrophores was also observed in the skin. These results indicate that androgen induces male-type nuptial coloration in the bitterling and that the responses of chromatophores to androgen differ with the type and distribution site of the chromatophores.

Insulin-like growth factor 1 (IGF1) is involved in the proliferation of mouse and rat endometrial cells in a paracrine or autocrine manner. Insulin-like growth factor binding protein-3 (IGFBP3) modulates actions of IGFs directly or indirectly. The present study aimed to determine whether IGFBP3 is involved in the regulation of proliferation of mouse endometrial cells. Mouse endometrial epithelial cells and stromal cells were isolated, and cultured in a serum free medium. IGF1 stimulated DNA synthesis by endometrial epithelial and stromal cells, and IGFBP3 inhibited IGF1-induced DNA synthesis. Estradiol-17β (E2) decreased the Igfbp3 mRNA level in endometrial stromal cells, whereas it increased the Igf1 mRNA level. Transforming growth factor α (TGFα) significantly decreased IGFBP3 expression at both the mRNA and secreted protein levels in endometrial stromal cells. Progesterone (P4) did not affect the E2-induced down-regulation of Igfbp3 mRNA expression in endometrial stromal cells, although P4 alone increased Igfbp3 mRNA levels. The present findings suggest that in mouse endometrial stromal cells E2 enhances IGF1 action through enhancement of IGF1 synthesis and reduction of IGFBP3 synthesis, and that TGFα affects IGF1 actions through modulation of IGFBP3 levels.

In 2003, we examined the chromosomes of grass voles at an illegal dumpsite at the Aomori-lwate prefectural boundary. In subsequent years, from 2003-2006, we surveyed the chromosomes of four species of small mammals, namely, the Japanese grass vole (Microtus montebelli), the large Japanese field mouse (Apodemus speciosus), the small Japanese field mouse (A. argenteus), and the greater Japanese shrew mole (Urotrichus talpoides). Each annual survey revealed, both on a yearly basis and during the entire period in question, that the frequencies of breaks and gaps in chromosomes of M. montebelli were significantly higher at the dumpsite than on the outskirts and in controls, suggesting that grass voles at the dumpsite have been subject to continuous genotoxic effects since the establishment of the dumpsite. We also ascertained that grass voles are much more susceptible to chromosomal damage than field mice and shrew moles, which had very low levels of chromosomal aberrations at the dumpsite, on the outskirts of the dumpsite, and in controls. Our four-year survey revealed two variants of M. montebelli from the dumpsite with M6 fission (2n=31), two variants of A. speciosus from the outskirts with XO monosomy (2n=47, XO), and a variant of A. speciosus from the dumpsite with situs inversus. Our analysis confirms our previously proposed hypothesis that M. montebelli might be useful as an indicator species for genotoxic assessment of below-ground pollution by industrial waste at illegal dumpsites.

Field studies conducted on rural red fox (Vulpes vulpes) populations suggest that the majority of males tend to disperse while the majority of females tend to be philopatric, that males disperse farther than females, and that most of the foxes disperse during their first year of life. However, the quantification of dispersal parameters is poorly documented in the red fox, because this carnivore is notoriously difficult to follow from birth to maturity. The aim of this study was to test hypotheses from field data with the help of a molecular analysis using six random amplified polymorphic DNA (RAPD) markers. The study was conducted on samples collected from 85 foxes in a French rural population. Genetic and geographical distances between pairs of individuals were calculated for the 3570 potential pairs originating from this population to determine whether the foxes had dispersed. High genetic diversity and an absence of genetic clusters among studied individuals support the occurrence of intense and constant gene flow in the study population, probably induced by dispersion. At least 16.2% of the potential pairs we studied were subject to dispersal. Sex-biased dispersion was not observed, apart from a sex bias in favor of females towards long-distance dispersal. A predominance of males that ultimately dispersed a long distance could not thus be confirmed. Furthermore, it seems that dispersal did not occur primarily in the subadult age class in our rural study area, but that some pairs of juveniles may also have been involved in dispersal.

The tongue of birds fills the oral cavity and has a beak-like shape. Morphological studies of birds reveal a correlation between the structure of the tongue and the mechanism of food intake and the type of food. However, several studies have shown morphological differences among the tongues of bird species. The aim of this study was to analyze ostrich tongue morphology and ultrastructural features using scanning electron microscopy. Tongues from 12 adult ostriches were examined. Six tongues were sectioned sagittally into lateral and middle portions, fixed in 10% formaldehyde solution, and examined under light microscopy. The other six samples were sectioned longitudinally, and the dorsal and ventral surfaces were separated, immersion-fixed in modified Karnovsky solution, and examined under scanning electron microscopy. The tongue surface of the ostrich was smooth, without lingual papillae, and covered by stratified non-keratinized epithelium. In the submucosal layer, mucous salivary glands were surrounded by connective-tissue capsules, with septa dividing the glands into lobes. Numerous salivary gland ducts of different sizes and connective-tissue laminae dividing each opening could be clearly seen in scanning electron microscope images. The ventral surface had fewer openings than the dorsal surface. In samples treated with NaOH, connective-tissue papillae from the dorsal region were oriented posteriorly.

In the vertebrate retina, it has been shown that a large number of neurons produced at the onset of neurogenesis die early in development. Since this apoptotic cell death occurs in a short, limited time, little is known in detail on its histocytology. Using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method, we investigated the apoptotic cells in the adult goldfish retina in which the progenitor cell keeps proliferating. Most of the TUNEL-positive nuclei were found in the marginal retina, about 40–200 µm from the circular blood vessel (CBV) running parallel to the retinal rim. The peak density was about 1400/mm² surface area at 90–130 µm from the CBV. Overall retinal cell density in the marginal retina was also studied by toluidine blue staining. The retinal cell density increased toward the central retina, reaching a peak density of 278,000/mm²at 130 µm from the CBV. It then decreased gradually to 228,000/mm² in the mature retina. This 18% reduction seemed to be caused by apoptosis. We also found a significant increase in the mean density of apoptotic cells in goldfish sacrificed at midnight, 403/mm², compared to that at midday, 217/mm². This increase was not seen in goldfish kept under either constant darkness or constant light.

We examined the effects of hyperosmotic stress on the gene expression and activity of neuronal nitric oxide synthase (nNOS) in the preoptic/hypothalamic neurosecretory system of the euryhaline tilapia Oreochromis mossambicus (Mozambique tilapia) by means of semiquantitative RT-PCR and NADPHd histochemistry. Expression of nos1 was rapidly and transiently up-regulated in the preoptic region and hypothalamus in response to a salinity change (70% seawater, SW). Expression levels increased 4 h after the salinity change and then returned to basal levels within 8 h of the hyperosmotic challenge. NADPHd histochemistry revealed that positive magnocellular and gigantocellular preoptic neurons increased in number 4 h after the salinity change, while the number of parvocellular preoptic neurons reactive for NADPHd showed no significant change. These results indicate that the nNOS gene expression and NOS activity are stimulated in the preoptic/ hypothalamic neurosecretory system in response to hyperosmotic stress and suggest that NO influences neuronal responses to short-term osmotic stimulation in euryhaline fish.

Wolbachia is a genus of maternally inherited, intracellular, alpha-Proteobacteria which are widespread among arthropods and cause various reproductive alterations such as cytoplasmic incompatibility and feminization. Wolbachia strains in arthropods have been phylogenetically divided into two supergroups, A and B. Here, we determined the phylogenetic relationships among Wolbachia strains harbored by insects and isopod crustaceans by using groE operon sequences, which encode highly conserved bacterial heat shock proteins. This study includes the first survey for Wolbachia in isopods from a Southeast Asian country, i.e., Thailand. Two isopod species from different parts of Thailand were found to be infected by Wolbachia. Their groE sequences were also included in the phylogenetic analysis. Our results showed clearly that 19 strains from tropical insects, 11 strains from French isopods, and two strains from Thai isopods were in the B supergroup, and 15 strains from tropical insects were in the A supergroup. This is the first report of phylogenetic analysis of a large data set comprising Wolbachia groE sequences from both insects and isopod crustaceans.