FG-9307, a cell line derived from a gill of the flounder, Paralichthys olivaceus, was used to determine the cytotoxic effects of the organophosphorus (OP) pesticide parathion. Cytotoxicity was measured by three endpoint systems: neutral red (NR) uptake assay, tetrazolium (MTT) assay and cell protein assay. The lowest concentration of parathion tested (1 mg/ml) was toxic and there was no significant difference in cytotoxic effects among the three assays. The FG-9307 cell line is a suitable bioindicator for the screening of the acute toxicities of parathion. The fine structures of the cells were also studied. Ultrastructures were markedly altered by parathion, as evidenced by dilation of nuclear membranes and mitochondrial cristae and by the presence of lysosomes with engulfed particles. With the increase of the parathion concentration, the damage degree of the cellular structures was more serious. At the highest concentration tested (15 mg/ml), there were few visible organelles, although such changes in cell morphology were not observed under a light microscope. Apparently, this is the unnoted report of marine fish cell line used for the evaluation of the acute in vitro cytotoxicity of parathion.

Amphioxus HMGB gene, AmphiHMGB, encoding a high mobility group (HMG) protein was identified from the gut cDNA library of Branchiostoma belcheri tsingtauense. Primary structural examination indicates that it is a member of HMGB family. Molecular phylogenetic analysis suggests that AmphiHMGB represents the archetype of chordate HMGB genes including HMGB1, HMGB2 and HMGB3 lthough it may have lost its C-terminal domain during evolution. Northern blotting revealed that AmphiHMGB expression was restricted mainly to guts in the adult, and AmphiHMGB transcripts were in greater abundance in gastrula and neurula though they were markedly low in 1-day larva.

Chromosome banding study remains lacking in amphioxus heretofore. This paper reports the C-band pattern of the metaphase chromosomes of amphioxus Branchiostoma belcheri tsingtauense, the first description of banded karyotype in cephalochordate. The C-banding showed that around 50% of the second chromosome pair examined was heteromorphic, while the remaining ones were homomorphic. In contrast, the other 17 pairs were all homomorphic. These broadly support our previous suggestion that the second chromosome pair is a pair of sex-chromosomes. The C-banding stained positively about 54.3% of the chromosome surface. Most of the centromeric and terminal regions in many chromosomes had positive C-bands, and some interstitial C-bands were also observed in some chromosomes. It seems clear that chromosomes of amphioxus are highly heterochromatinized. In addition, silver staining revealed a single pair of nucleolar organizer regions (NORs) located in the telomeric regions of mediumsized chromosomes. It is suggested that the number and location of NORs in amphioxus represent the primitive condition for chordates.

In thiss tudy, a member of the MyoD gene family, AmphiMDF, wasis olated from the embryos of amphioxusby degenerate PCR, followed by rapid amplification of cDNA ends (RACE). Southern blot analysis confirmed that only a single myogenic bHLH gene waspres ent in the genome of amphioxus Branchiostoma belcheri tsingtauense. Sequence and phylogenetic analyses indicated that AmphiMDF falls at the base of its vertebrate homologs. The amino acid sequence of AmphiMDF was almost equally similar to those of the four clusters of the vertebrate MyoD family. This suggests that AmphiMDF is not only the sister but also the archetype of the vertebrate myogenic bHLH genes. The scenarios to explain the origin of the vertebrate MyoD gene family from the ancestral myogenic bHLH gene like AmphiMDF are also discussed.

The humoral fluid of Branchiostoma belcheri tsingtauense was examined for the presence of complement-like activity. The humoral fluid showed hemolytic activity for rabbit erythrocytes and those from species representing mammals, birds, amphibians and fish, but not sensitized sheep rythrocytes. There was no relationship between phylogeny of the target erythrocytes and degree of hemolysis. The hemolytic activity was optimally assayed at 20℃, at pH 7.5, and in the presence of 10mM Mg2+. The hemolytic activity was Mg2+ -dependent and heat-sensitive, and was abrogated by treatment with rabbit anti-human C3 serum, zymosan, methylamine, hydrazine, and henylmethylenesulfonyl fluoride. In addition, Western blotting and titration by turbidimetric immunoassay (TIA) revealed that amphioxus humoral fluid contained C3 component, and its oncentration is about 1.17mg/ml, which is comparable to C3 concentration in human or dog sera. These suggest that the hemolytic activities displayed by amphioxus humoral fluid appear to represent the vertebrate complement system probably operating via the alternative pathway.