Nutritional diagnosis of phytoplankton in Lake Baikal

To diagnose the nutritional status of phytoplankton in Lake Baikal, surveys for the determination of concentrations of particulate carbon (PC), nitrogen (PN) and phosphorus (PP) and their ratios were conducted at six stations in March, June, August and October 1999. The concentrations of PC and PN were lower than, and those of PP were similar to, those in another mesotrophic lake except at the station near the mouth of the largest input river, Selenga River, of Lake Baikal. The PC : PN : PP ratio was 102 : 13 : 1, considerably close to the Redfield ratio. The ratio was constant against spatiotemporal changes. These indicate that phytoplankton in Lake Baikal were exposed to no deficiency in nitrogen nor phosphorus. From a viewpoint of the nutritional status of phytoplankton, Lake Baikal might be viewed as an ocean rather than as a lake.     

A mutation in the serum and glucocorticoid-inducible kinase-like kinase (Sgkl) gene is associated with defective hair growth in mice.

YPC is a mutant mouse strain with defective hair growth characterized by thin, short hairs and poorly developed hair bulbs and dermal papillae. To identify the gene associated with the phenotype, we performed genome-wide linkage analysis using 1010 backcross progeny and 123 microsatellite markers covering all chromosomes. The mutant locus (ypc) was mapped to a 0.2-cM region in the proximal part of mouse chromosome 1. This 0.2-cM region corresponds to a 450-kb region of genome sequence that contains two genes with known functions and five ESTs or predicted genes with unknown functions. Sequence analysis revealed a single C-to-A nucleotide substitution at nucleotide 1382 in the Sgkl gene, causing a nonsense mutation at codon 461. Sgkl encodes serum and glucocorticoid-inducible kinase-like kinase (SGKL), which belongs to a subfamily of serine/threonine protein kinases and has been suggested to have a role downstream of lipid signals produced by activation of phosphoinositide 3-kinase (PI3K). In the mutant SGKL, a serine residue in the C-terminal end of the protein (Ser486), which is indispensable for activation of SGKL upon phosphorylation, is abolished by premature termination. Specific expression of the Sgkl gene in the inner root sheath of growing hair follicles was also identified by in situ hybridization. Therefore, we concluded that the nucleotide substitution in the Sgkl gene is the causative mutation for defective hair growth in the ypc mutant mouse and that the signaling pathway involving SGKL plays an essential role in mammalian hair development.     

Dissecting calvarial bones and sutures at single-cell resolution

Cranial bones constitute a protective shield for the vulnerable brain tissue, bound together as a rigid entity by unique immovable joints known as sutures. Cranial sutures serve as major growth centres for calvarial morphogenesis and have been identified as a niche for mesenchymal stem cells (MSCs) and/or skeletal stem cells (SSCs) in the craniofacial skeleton. Despite the established dogma of cranial bone and suture biology, technological advancements now allow us to investigate these tissues and structures at unprecedented resolution and embrace multiple novel biological insights. For instance, a decrease or imbalance of representation of SSCs within sutures might underlie craniosynostosis; dural sinuses enable neuroimmune crosstalk and are newly defined as immune hubs; skull bone marrow acts as a myeloid cell reservoir for the meninges and central nervous system (CNS) parenchyma in mediating immune surveillance, etc. In this review, we revisit a growing body of recent studies that explored cranial bone and suture biology using cutting-edge techniques and have expanded our current understanding of this research field, especially from the perspective of development, homeostasis, injury repair, resident MSCs/SSCs, immunosurveillance at the brain's border, and beyond.     

Changes in immunohistochemical distribution of cytochrome MC-P-448 in the rat liver during acclimation to cold

Immunohistochemical localization of cytochrome MC-P-448 (form of cytochrome P-450 induced by methylcholanthrene) in rat hepatic lobule and the changes in their distribution pattern in response to cold exposure at 4°C were investigated. The distribution of hepatocytes expressing immunoreactivity to cytochrome MC-P-448 was demonstrated with rabbit anti-MC-P-448 serum using a microphotomeasurement system P1 (Nikon). A duration of cold exposure for 1, 2, 3 or 4 weeks at 4°C was applied to study the effect of cold adaptation of cytochrome MC-P-448. In control rats housed at 24°C, hepatocytes showing high immunoreactivity to cytochrome MC-P-448 were located in the centrilobular areas of the hepatic lobules, whereas they disappeared markedly in the 4-week cold-exposed rats. In 1-week and 2-week cold-exposed rats, only a slight decrease in the expression of MC-P-448 positive hepatocytes was observed. These changes were clearly seen by visual inspection of the distribution topography as determined by a microphotomeasurement technique. In conclusion, cytochrome MC-P-448 forms which were predominantly located in centrilobular areas in the hepatic lobule decreased in 4-week cold-exposed rats. This was in contrast to our early report which showed an increasing tendency of cytochrome PB-P-450 forms in 4-week cold-exposed rats.     

Chemical characterization of the serum very low density and high density lipoproteins from bullfrog, Rana catesbeiana.

The chemical properties of very low density and high density lipoproteins of adult bullfrog serum were determined. This serum contained extremely low levels of both very low density lipoprotein (10-30 mg/100 ml) and high density lipoprotein (5-10 mg/100 ml). The constituents of very low density lipoprotein, on a weight percentage basis, were found to be 48.1% triglyceride, 17.3% cholesterol ester, 8.8% cholesterol, 11.6% phospholipid, and 12% protein. These constituents were also present in high density lipoprotein with weight percentage values of 3.7%, 19.3%, 11.9%, 25.2%, and 36.8%, respectively. The fatty acid compositions of the triglycerides, cholesterol esters, and phosphatidylcholine were quite similar in the very low density lipoprotein and high density lipoprotein. However, shingomyelin fatty acid composition was appreciably different in the two lipoproteins. Disc gel electrophoresis in sodium dodecyl sulfate-polyacrylamide gels produced patterns with one major (approximate molecular weight, 7,000) and several minor bands for the apoprotein of very low density lipoprotein and one major (approximate molecular weight, 28,000) and several minor bands for that of high density lipoprotein.     

The production-to-respiration ratio and its implication in Lake Biwa,Japan

Production-to-respiration (P:R) ratio was estimated at an offshore site of Lake Biwa in order to examine whether the plankton and benthic community is subsidized with allochthonous organic carbon, and to clarify the role of this lake as potential source or sink of carbon dioxide. The respiration rate of protozoan and metazoan plankton was calculated from their biomass and empirical equations of oxygen consumption rates, and that of bacterioplankton was derived from their production rate and growth efficiency. In addition, the carbon mineralization rate in the lake sediments was estimated from the accumulation rate of organic carbon, which was determined using a ²¹⁰Pb dating technique. On an annual basis, the sum of respiration rates of heterotrophic plankton was comparable to net primary production rate measured by the ¹³C method. However, when the mineralization rate in the lake sediments was included, the areal P:R ratio was 0.89, suggesting that Lake Biwa is net heterotrophic at the offshore site with the community being subsidized with allochthonous organic carbon. Such a view was supported by the surface water pCO₂ that was on average higher than that of the atmosphere. However, the estimate of net CO₂ release rate was close to that of carbon burial rate in the sediments. The result suggests that the role of Lake Biwa in relation to atmospheric carbon is almost null at the offshore site, although the community is supported partially by organic carbon released from the surrounding areas.     

Recombinase-mediated mouse transgenesis by intracytoplasmic sperm injection

The low efficiency of current microinjection-based animal transgenesis techniques is largely the result of poor embryo survival. We have developed a new, bacterial recombinase-based transgenesis method. Intracytoplasmic sperm injection (ICSI) of single stranded DNA (ssDNA) complexed with E. coli recombinase RecA into mouse metaphaseII (MII) arrested oocytes resulted in RecA-dependent transgenesis. This approach offers significant advantages over pronuclear microinjection and previous ICSI-based transgenesis approaches in terms of improved embryo survival, which translates into greater transgenesis efficiency. It also opens the possibility to attempt experiments, which may affect gene targeting by homologous recombination into DNA of mammalian single celled pre-implantation embryos.     

Changes of body temperature and extracellular serotonin level in the preoptic area and anterior hypothalamus after thermal or serotonergic pharmacological stimulation of freely moving rats

Although many studies has been shown that serotonin (5-HT) in the preoptic area and anterior hypothalamus (PO/AH) is important for regulating body temperature (Tb), the exact role is not established yet due to conflicting results probably related to experimental techniques or conditions such as the use of anesthesia. The purpose of present study was to clarify the role of 5-HT in the PO/AH using the combined methods of telemetry, microdialysis and high performance liquid chromatography (HPLC), with a special emphasis on the regulation of Tb in freely moving rats. Firstly, we measured changes in Tb and levels of extracellular 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the PO/AH during cold (5 degrees C) and heat (35 degrees C) exposure. We also perfused fluoxetine (5-HT re-uptake inhibitor) and 8-hydroxy-2-(Di-n-propylamino)tetralin (8-OH-DPAT: 5-HT1A agonist) into the PO/AH. During both exposures, although Tb changed significantly, no significant changes were noted in extracellular levels of 5-HT and 5-HIAA in the PO/AH. In addition, although perfusion of fluoxetine or 8-OH-DPAT into the PO/AH increased or decreased extracellular 5-HT and 5-HIAA levels in the PO/AH respectively, but Tb did not change at all. Our results suggest that 5-HT in the PO/AH may not mediate acute changes in thermoregulation.