Comparison On Isozymes And Gonadal Development Of Two Lancelets And Study On Chromosome Of Branchiostoma Belcheri

The amphioxus or lancelets, belonging to Subphylum Cephalochordata, Phylum Chordata, are considered to be basal chordates and have long occupied a key place in studying the origin and evolution of vertebrates. In China, the lancelets, mainly distributed in Xiamen and Qingdao, has been enlisted as second grade national protected animals. The research is based on the isozyme of two lancelets(Branchiostoma belcheri and B. japonicum) from Xiamen Waters, gonadal development of two lancelets cultured in the laboratory and the chromosomes of Branchiostoma belcheri.When comparing the phenotype of the four kinds of isozymes (LDH, MDH, SOD, EST) between two lancelets by a vertical flat-bed discontinuous polyacrylamide gel electrophoresis techenique, we found that there were significant differences in the number, location and staining intensity of enzyme spectrum between two lancelets, as well as between female and male in the same species.Cultured in the laboratory, the two lancelets can develop and mature their gonads, and spawn spontaneously. For B. belcheri, the gonad start to develop in April and mature from late May with the peak in the period from June to July, and the spawning occur in the period from July to August with the peak in July. For B. japonicum, some individuals had matured the gonad in Feburary and the peak occur in April, and the spawn occur in late April. This has slightly difference from those under natural conditions. In addition, the whole cycle of gonadal development was divided into seven stages:Undeveloped, StageⅠ,Ⅱ,Ⅱ,Ⅳ,Ⅴand Post-spawning period. The characteristic was described morphologically and histologically.The metaphase chromosomes were prepared from embryonic cells of B. belcheri and the karyotype was analysed preliminarily. The results indicate the karyotype formula of B. belcheri is 2n=40=2sm+2st+36t, NF=42. The G-banding was carried out by the standard trypsin method. The G-banding results show that there are a total of 174 G-banded, including 93 positive and 81 negative, in the metaphase chromosome of B. belcheri.Using the methods described by Sumner (1972) with minor modification, the C-bands were presented in all 40 chromosomes of B. belcheri, especially in the centromere regions. The total numbers of C-bands are 59, including 31 positive,23 negative and 5 variable bands.Ag-staining was performed according to Howell & Black (1980). The results show the positive staining present in all 40 chromosomes in B. belcheri instead of specificity of nucleolar organizing region (NOR). The Ag-staining belts locate in telomere, centromere and median of chromosome.