Histological observation of the pituitary-thyroid axis of a neotenic fish (the ice fish, <Emphasis Type="Italic">Salangichthys microdon</Emphasis>)

ABSTRACT:   In order to study the physiological characteristics of neoteny in teleosts, the development of the thyroid axis and digestive tract of the ice fish, Salangichthys microdon (Salmonoidei), were examined using wild caught samples in the Yura River and its estuary. In all developmental stages examined in this study, the digestive tract was straight, and no gastric gland was observed, even in adults. Since these features are only observed in larval stages of a related species, ayu, Plecoglossus altivelis (Salmonoidei), it is suggested that the ice fish retains larval features, not only in appearance but also in internal organs. Additionally, the thyroid axis exhibited a unique characteristic. Until the end of the juvenile stage, thyroid glands remained inactive, and no thyroid stimulating hormone (TSH) cells were observed. Activation of the thyroid gland and the first appearance of TSH cells occurred in adults. Since activation of the thyroid axis was generally known to occur by the time larval have transformed to juveniles in several teleosts, a delayed functioning of the thyroid axis was suggested as a specific characteristic, and probably a major factor contributing to neotenic development of the ice fish.     

Effect of oral administration of a single bolus of six different protein sources on digestive physiology of red seabream Pagrus major juveniles

Fish Physiology and Biochemistry - To reveal direct effects of various protein sources on digestive physiology of red seabream, Pagrus major (38.5 ± 0.4&nbsp;g), six different...     

Morphology, endocrinology, and environmental modulation of gonadal sex differentiation in teleost fishes

Successful reproduction by an adult depends on the normal ontogenesis of the gonads, a complex process of cellular and histological differentiation that starts early in life. This process is theoretically predetermined by genetic factors and includes sensitisation of the bipotential gonads to endogenous endocrine factors prior to, during and even after commitment to maleness or femaleness. However, young fish are relatively vulnerable to a host of environmental (physical and chemical) factors that can affect this endogenous endocrine axis, disturbing or even overriding the putative developmental pathway. This sexually lability can be exploited to our advantage for the production of monosex fish populations of the most valuable sex for food production or aquarium fish trade. On the other hand, it represents also a potential path for undesirable influences from endocrine-disrupting chemicals and climatic factors, particularly environmental temperature. This paper provides a detailed account of the early histological process of gonadal sex differentiation, with special reference to gonochoristic species, and reviews the criteria employed to positively identify ovarian and testicular differentiation. It also reviews the development of endocrine competence and sensitivity of the differentiating gonads to exogenous influences in the context of the relative stability of genotypic sex determination in various fish species. Sex differentiation in some species seems to be under strong genetic control and may not require endogenous sex steroid production. Conversely, reliance on endogenous sex steroids for gonadal differentiation is observed in other species and this phenomenon is apparently associated with a higher incidence of environment (mainly temperature)-labile sex differentiation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Expression analysis of the type I keratin protein keratin 33A in goat coat hair

The coat of a goat, like that of many mammalian species, consists of an outer coat of coarse hairs and an under coat of fine, downy hairs. The coarse guard hairs are produced by primary follicles and the finer cashmere hairs by secondary follicles. We previously reported that hair keratins are components of cashmere hair, and proteomic analysis revealed that their expression is elevated in winter coat hair. To determine detailed characterization, we have cloned keratin 33A gene, a major highly expressed keratin in winter, and then analyzed the expression of goat hair coat. By Western analysis, we detected that keratin 33A protein is expressed only in hair coat among the various goat tissues. Moreover, the expression level in winter has increased in cashmere high‐producing Korean native breed, whereas the expression levels between summer and winter had not changed in cashmere low‐producing Saanen. In addition, by immunohistochemistry we determined that keratin 33A is localized in the major cortex portion of cashmere fiber. These results confirm that keratin 33A is a structural protein of goat cashmere hair fiber.     

Two concepts on the immunological aspect of blastocyst implantation

The process of blastocyst implantation is a series of interactions between the blastocyst and maternal tissues. The purpose of this process is (1) to provide nourishment to the embryo for developmental growth in appropriate physiological and endocrinological environment until a placenta is established, and (2) to protect the (semi-)allogeneic embryo from any attacks from the maternal immune system. To facilitate successful implantation, therefore, these two aspects of the embryonic demand must be satisfied in the embryo-maternal interface throughout the entire process of implantation. The first concept I present in this paper is that blastocyst implantation essential factors (BIEFs) have dual functions: one, for structural and functional modification of the endometrium to accommodate the developing embryo and provide nourishment and suitable environment for its development, and the other, for modulation, directly or indirectly, of the maternal immune system to prevent attacks by the maternal immune system. The second concept is that BIEFs convert the endometrium (or uterus) from an immunologically non-privileged site to a privileged site. This endometrial (uterine) conversion is the immunological aspect of the blastocyst implantation process. When the endometrium has become receptive for blastocyst implantation, it signifies that the immunological conversion of the endometrium by BIEFs has been sufficiently attained to let the embryo start contacting maternal tissues. During the early stages of placentation, as the trophoblast cells differentiate and make their way to the maternal blood vessels to establish the placenta, BIEFs continuously provide nourishment and immunological protection to the developing embryo. The immunological protection of the embryo/fetus from potential attacks by the maternal immune system appears to reach a peak at the time of establishment of the placenta. Thus, clarification of the roles of BIEFs in both the physiological/endocrinological aspect as well as the immunological aspect is essential for understanding the biological process of implantation.     

Detection of DNA of 'Candidatus Mycoplasma haemominutum' and Spiroplasma sp. in unfed ticks collected from vegetation in Japan

DNA fragments of 'Candidatus Mycoplasma haemominutum', a feline heamobartonella pathogen, were detected from unfed Ixodes ovatus collected from vegetation in Hokkaido, Fukushima and Yamaguchi Prefectures, and unfed Haemaphysalis flava in Yamaguchi Prefecture. This finding suggests that ixodid tick is a possible vector of 'C. Mycoplasma haemominutum'. Spiroplasma DNA was also detected from unfed I. ovatus in Hokkaido, Fukushima and Yamaguchi Prefectures. The analysis of nucleotides sequence suggested that this Spiroplasma was distinct from registered species.     

Experimental challenges of juvenile and adult Manila clams with the protozoan Perkinsus olseni at different temperatures

Infection with Perkinsus species, primarily P. olseni, is thought to be a major cause of the decline of Manila clam populations in Japan since the 1980s. However, the pathogenicity of the infection has not been sufficiently evaluated to estimate the impact of infection on wild Manila clam populations. We experimentally challenged juvenile (3- to 6-mm shell length) and adult (18- to 22-mm shell length) Manila clams with P. olseni at 18, 23, 28, and 30 °C. Mortality was significantly higher in challenged groups than in control groups. The difference in mean mortality between the challenged and control groups (all life stages and temperatures) was only significant above a threshold of infection intensity ~10⁶ cells/g soft wet tissue (SWT). As temperature increased, the onset of mortality occurred more rapidly. The increase in mortality occurred earlier in juveniles than adults at 28 °C and lower. Our results suggest that the pathogenicity of P. olseni is higher in juveniles than in adults and at higher water temperatures. Given the infection intensities (ca. 10⁶ cells/g SWT) previously reported in wild Manila clams, the parasite likely has considerable impact on wild Manila clam populations, particularly juveniles during periods of high temperature.     

Genetic diversity and pathogenic characteristics of Phomopsis asparagi obtained from Asparagus officinalis and A. kiusianus in Japan

Journal of Plant Diseases and Protection - Phomopsis asparagi has been reported as a serious disease, causing stem blight on asparagus cultivars (Asparagus officinalis), and this fungus was also...     

Diesel exhaust particle toxicity on spermatogenesis in the mouse is aryl hydrocarbon receptor dependent

Diesel exhaust particles (DEPs) are particulate matter from diesel exhaust containing many toxic compounds, such as polyaromatic hydrocarbons (PAHs). Some toxicities of PAH are considered to express via aryl hydrocarbon receptor (AhR). We hypothesized that the male reproductive toxicity of DEPs may depend on PAHs. BALB/c male mice received 24.7, 74.0 or 220 microg/mouse DEP suspension or vehicle injected into the dorsal subcutaneous layer 10 times during 5 weeks. The mice were euthanized, and blood and organs were collected 2 weeks after the last treatment. The epididymis weights, relative epididymis weights per body weight and daily sperm productions and viabilities of the 74.0 and 220 microg/mouse DEP-treated groups decreased significantly compared with those of the vehicle group. The total incidence of sperm abnormalities in the 74.0 and 220 microg/mouse DEP-treated groups increased significantly compared with the vehicle group. The seminiferous epithelium area ratios of the 74.0 and 220 microg/mouse DEP-treated groups were significantly higher compared with the vehicle and 24.6 microg/mouse DEP-treated groups. The ratios of seminiferous tubules with elongated-type spermatids in the 74.0 and 220 microg/mouse DEP-treated groups were significantly decreased compared with the vehicle group. The testosterone level and hepatic ethoxyresorufin-O-deethylase (EROD) activity as an indirect index of AhR activity in the 74.0 microg/mouse DEP-treated group were significantly increased compared with those of the vehicle group. These results clearly demonstrated that DEPs suppress testicular function, especially spermatogenesis and sperm motility. These effects may be AhR dependent.     

The variation of ferrous iron content and soil profiles under flooded condition of rice field (Part 1)

Rice fields are kept under flooded condition during the growing period of rice plant for at least three months. Soil of rice fields therefore shows consequently remarkable differences as compared with that of upland fields. This may be understood as a kind of redoxy system. Many soil constituents suffer big changes during floodtime. One of the most important constituents is iron because of its abundance in soil and its color change.