Molecular mechanism of evolution and morphological diversity in Cladocera.

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(1) Hemoglobin (Hb) purified from the water flea, Daphnia magna, was analyzed by two-dimensional gel electrophoresis. The Hb was shown to be composed of 6 major subunit chain species. The NHィイD22ィエD2-terminal amino acid sequences of the 6 Hb chains showed that at least 4 Hb genes are present in D. magna. The Hb genes were differentially regulated by the ambient oxygen concentration. Four Hb genes constituted a cluster on the chromosome of D. magna. The complete nucleotide sequences of these genes and their cDNAs showed that the genes have a seven-exon, six-intron structre. A cDNA homologous to that for Arnt, a subunit of transcriptional factor HIF1α which plays a major role in response to hypoxia in mammalian cells, was isolated from D. magna and then its complete nucleotide sequence was determined.(2) cDNAs homologous to those of Drosophila Hox genes, Antp, Ubx, Abd-A, and Scr, and other developmental genes, dll, wnt-1, and hedgehog, were isolated from D. magna and then their complete uncleotide sequences were determined. Expression patterns of these cDNAs during development of D. magna embryos were analyzed by whole mount in situ hybridization. Daphnia Antp cDNA was expressed in Drosophila embryos using the Gal4/UAS system. While it retained the same functions as those of Drosophila Antp, such as the ectopical induction of teashirt and decapentaplegic genes, it showed some functions different from those of Drosophila Antp.