Zoological Science

Troponin regulates contraction of vertebrate striated muscle in a Ca²⁺-dependent manner. More specifically, it acts as an inhibitor of actin-myosin interaction in the absence of Ca²⁺ during contraction. In vertebrates, this regulatory mechanism is unlike that in some less highly derived taxa. Troponin in the smooth muscle of the protochordate ascidian species Halocynthia roretzi regulates actinmyosin contraction as an activator in the presence of Ca²⁺, not as an inhibitor in the absence of Ca²⁺ as is the case in vertebrates. In this study, contractile regulation of striated muscle from another protochordate, the amphioxus Branchiostoma belcheri, was analyzed using recombinant troponin components TnT, TnI, and TnC that were produced in an Escherichia coli expression system to further elucidate their roles in Ca²⁺-dependent regulation of the actin-myosin interaction. Combination of these troponin components in an actin-myosin ATPase activity assay showed that troponin in amphioxus striated muscle functions in a similar manner to troponin in vertebrate striated muscle, and differently from ascidian smooth muscle troponin. Thus, troponin function appears to have evolved differently in different protochordate muscles.

Murine recessive yellow (Mc1r ^e) is a loss-of-function mutation in the receptor for α-melanocyte-stimulating hormone, melanocortin receptor 1 (Mc1r), and results in a yellow coat by inducing pheomelanin synthesis in hair follicular melanocytes. We previously showed that eumelanin and pheomelanin content in dorsal hair in female Mc1r ^e/Mc1r ^e mice 5 weeks after birth was greater than that in male mice. To better understand the sex difference in hair pigmentation, estrogen, progesterone, and androgen were injected subcutaneously to newborn mice, and the effects of these sex hormones on hair pigmentation at 8.5 days were investigated. Although these sex hormones failed to affect the ratio of pheomelanic to eumelanic hair, they increased total hair pigmentation. Chemical analyses showed that total melanin content was increased by a low dose of estrogen in female mice. Moreover, estrogen increased pheomelanin content in female hair, whereas the hormone greatly decreased both eumelanin and pheomelanin content in male hair. High doses of progesterone, in contrast, increased total melanin content in both female and male hair. Moreover, a high dose of androgen increased total melanin content exclusively in male hair. These results suggest that estrogen is the main factor in determining the higher content of eumelanin and pheomelanin in female hair of Mc1r ^e/Mc1r ^e mice.

MicroRNAs are single-stranded RNA molecules with a length of 19–25 nucleotides, which play roles in various biological phenomena, including development, differentiation, apoptosis, by regulating target gene expression. Although the presence of microRNA molecules in sea urchin and the expression of genes involved in microRNA biogenesis during sea urchin development have been reported recently, the function of microRNA in sea urchin development remains to be elucidated. In this study, to understand the function of microRNA in the early development of sea urchin, we focused on Dicer, an essential enzyme for biosynthesis of mature microRNA. We determined the nucleotide sequence of cDNA for a Dicer homolog in the sea urchin, Hemicentrotus pulcherrimus, HpDcr, and found that functional domains of Dicer proteins are conserved in HpDcr. Analyses of its pattern of expression showed that HpDcr mRNA is expressed in embryos at all developmental stages analyzed, and seems to distribute asymmetrically at the morula and later stages. Knockdown of HpDcr resulted in anomalous morphogenesis, such as impairment of gastrulation and skeletogenesis at the mesenchyme blastula stage and later stages, and alteration of mRNA levels of cell type-specific genes. Thus, HpDcr plays important roles in morphogenesis in sea urchin embryos, suggesting that miRNA could be involved in the early development of sea urchin by regulating target gene expression.

The Hengduan Mountains, situated in the southeastern Tibetan Plateau, have undergone dramatic geological and climatic changes over the Pleistocene epoch. Several studies have revealed that the mountains served as a refugium during the ice age. The large white-bellied rat Niviventer excelsior is a rodent endemic to the Hengduan Mountains, which makes it an appropriate species for investigating the influence of glacial movements on the genetic structure of mammals. In this study, we sequenced the partial mitochondrial DNA control region from 72 N. excelsior specimens collected from 20 localities. The results revealed very high levels of haplotype diversity (h = 0.947) and nucleotide diversity (π = 0.101) in this species. No common haplotype was found to be shared in samples from all geographic regions. Demographic analyses suggested that N. excelsior populations had not been subject to either expansion or bottleneck. The phylogenetic relationships among the haplotypes have no correlation with their geographical origins, while topology revealed two major clades. We speculate that the populations of N. excelsior may have been restricted to two separate refugia during the Last Glacial Maximum (0.60–0.17 Mya), with one west and one east of the Shaluli Mountains. Between the two major refugia, there existed a more widely distributed network subrefugia, which conserved genetic variations in N. excelsior. These results indicated that complex topographic configuration in the Hengduan Mountains provided a network of refugia to maintain the high level of genetic diversity in Pleistocene glaciations.

Partial nucleotide sequences (∼8000 bp) of the mitochondrial DNA of two cerithioidean gastropod species—Cerithidea djadjariensis and Batillaria cumingi—were determined. The order of mitochondrial genes (eight protein genes, two ribosomal RNA genes, and nine transfer RNA genes) was identical between these two species. and remarkably different from the previously reported order in other gastropods. The results indicate that the genome structure of the common ancestor of Cerithioidea and its sister group, Hypsogastropoda, is almost identical to that of the common ancestor of Gastropoda; moreover, independent mitochondrial genome rearrangements were identified between the lineages of Cerithioidea and Hypsogastropoda. The rearrangements within Cerithioidea can be explained by the inversion of a single tRNA gene, two translocations of a single tRNA gene, and three translocations of a genome fragment containing a tRNA gene and protein-coding gene(s).

The source areas of the Japanese populations of the masked palm civet Paguma larvata (Viverridae, Carnivora), an alien species in Japan, have not been identified. In the present study, to reveal their origins and genetic features, we determined the full mitochondrial DNA cytochrome b sequences (1,140 base-pairs) of a total of 206 individuals of P. larvata from the Honshu and Shikoku islands of Japan (186 animals) and Taiwan (20 animals), and investigated their molecular phylogeography and the genetic relationships between populations in these countries. We found that each animal from Japan exhibited one of four haplotypes (JA1, JA2, JA4, and JA5), and that JA1 and JA4 were more frequent in eastern Honshu and Shikoku—central Honshu, respectively. By contrast, six haplotypes consisting of four new types (TW1, TW2, TW3, and TW4) and the previously reported two types (JA1 and JA4) were identified from 20 animals from native populations in Taiwan. Within Taiwan, one haplotype set (JA1, TW1, and TW2) was distributed in the western region, while a second (JA4, TW3, and TW4) was found in the eastern region; these regions are separated by high mountain ranges. Our comparison of haplotype distributions strongly demonstrated that the eastern Japanese populations originated from animals of western Taiwan, and that the western Japanese populations originated from those of eastern Taiwan. In addition, the lower genetic variability and particular distribution patterns of haplotypes in Japan showed founder effects, which may have resulted from multiple introductions of P. larvata to Japan from Taiwan.

We studied age-related sexual dimorphism of the terminal abdominal ganglion in the cricket, Gryllus bimaculatus using osmium/ethyl-gallate staining and GABA immunohistochemistry. We determinedthat the volume of the terminal abdominal ganglion increases with increasing body size. The growth ratio between longitude and width in the terminal abdominal ganglion is the same in all nymph stages and sexes. However, the longitudinal growth of the male terminal abdominal ganglion ceases in the 8th instar and the adult stage. Therefore, in the adult stage, sexual dimorphism is observed in ganglion morphology. Additionally, sexual dimorphism is also observed in numbers of neuronal somata and GABA-like immunoreactive neurons in the terminal abdominal ganglion. At the beginning of the 8th instar, the number of somata is greater in female crickets than in males. GABA-like immunoreactive neurons, which were classified into eight clusters, increased between the 8th instar and adult in both sexes, but their numbers were sexually dimorphic in the 7th and 8th instars, and in the adult. Females had a greater number of GABA-like immunoreactive neurons than males. These differences occurred mainly in the 8th neuromere cluster, as well as the anterior region of the 9–11th neuromeres.

The topography of cone oil droplets and their carotenoids were investigated in the retina of jungle crow (Corvus macrorhynchos). Fresh retina was sampled for the study of retinal cone oil droplets, and extracted retinal carotenoids were saponified using methods adapted from a recent study, then identified with reverse-phase high-performance liquid chromatography (HPLC). To assess the effects of saponification conditions on carotenoid recovery from crow retina, we varied base concentration and total time of saponification across a wide range of conditions, and again used HPLC to compare carotenoid concentrations. Based on colors, at least four types of oil droplets were recognized, i.e., red, orange, green, and translucent, across the retina. With an average of 91,202 /mm², density gradually declines in an eccentric manner from optic disc. In retina, the density and size of droplets are inversely related. In the peripheral zone, oil droplets were significantly larger than those of the central area. The proportion of orange oil droplets (33%) was higher in the central area, whereas green was predominant in other areas. Three types of carotenoid (astaxanthin, galloxanthin and lutein), together with one unknown carotenoid, were recovered from the crow retina; astaxanthin was the dominant carotenoid among them. The recovery of carotenoids was affected by saponification conditions. Astaxanthin was well recovered in weak alkali (0.06 M KOH), in contrast, xanthophyllic carotenoids were best recovered in strong alkali (0.6 M KOH) after 12 h of saponification at freeze temperature.

We studied the reproductive biology and adaptability of the alien freshwater crangonyctid amphipod Crangonyx floridanus, currently inhabiting a large portion of Japan, both in the field and under controlled laboratory conditions. In the Chikuma River population of this alien amphipod, egg-bearing individuals were found throughout the year. In terms of egg maturation cycle, egg development (during embryogenesis), and egg count per ovipositional cycle, these amphipods display a very efficient reproductive system. This study also established their adaptability to a wide range of water temperatures (primarily 4–20°C, however in some cases, these individuals are able to survive at up to 30°C). C. floridanus's strong capacity to adapt to broad and variable environmental conditions is certainly contributing to its high rate of population increase, and rapid dispersion throughout Japan.

Three inkless octopodids are described from the continental shelf off southeastern South America. These octopuses are a non-commercial by-catch in the Falkland Islands fishery. Muusoctopus eureka (Robson, 1929) is one of two common inkless octopuses and is of medium size, with orange-pink skin and a distinctive pattern of irregular dark markings, interspersed with white spots visible only in living or freshly dead specimens. The second common inkless octopus is M. longibrachus akambei, a new subspecies of the Chilean species Muusoctopus longibrachus (Ibáñez, Sepúlveda and Chong, 2006). It has slender arms and is much larger at full maturity than M. eureka. It is a plain orange color when alive, pinkish cream when preserved. Muusoctopus bizikovi, sp. nov., is a smaller, rarer species, colored wine-red whether alive or preserved, and has a vestigial ink duct between the digestive gland and the anus. Relations with other species are discussed. This group of octopuses has often been associated with the genus Benthoctopus Grimpe, 1921, which is a junior synonym of Bathypolypus Grimpe (a genus of small species characterized by much shorter arms and males with a robust copulatory organ bearing transverse lamellae). It is argued that the misleading characterization of the so-called Benthoctopus group of species as “smooth skinned” is based upon the artefactual appearance of specimens fixed and preserved suboptimally following a detrimental freeze-thaw cycle of fisheries material previously frozen while at sea.