The bivoltine silkworm Bombyx mori （Lepidoptera： Bombycidae） exhibits a maternally controlled embryonic diapause. Maternal silkworms decide whether to lay diapause or nondiapause eggs depending on environmental fac...The bivoltine silkworm Bombyx mori （Lepidoptera： Bombycidae） exhibits a maternally controlled embryonic diapause. Maternal silkworms decide whether to lay diapause or nondiapause eggs depending on environmental factors such as the temperature and photoperiod during the egg and larval stages, and then induce diapause eggs during the pupal stage. However, little is known about the molecular mechanism that conveys the outcome of whether to produce diapause or nondiapause eggs from the egg or larval stages to the pupal stage. This study used microarray analysis to investigate differentially expressed genes in the larval brains of diapause- and nondiapause-egg producers, to which bivoltine silkworms were destined by thermal or photic stimulation during the egg stage. The cytochrome P450 18al and Kriippel homolog i genes were upregulated in producers of diapause eggs compared with those of nondiapause eggs under both experimental conditions. Cytochrome P450 18al encodes a key enzyme for steroid hormone inactivation and Krfippel homolog 1 is an early juvenile hormone-inducible gene that mediates the repression of metamorphosis. The upregulation of these genes during the larval stage might be involved in the signaling pathway that transmits information about the diapause program from the egg stage to the pupal stage in the silkworm.展开更多
Insects produce silk for a range of purposes. In the Lepidoptera, silk is utilized as a material for cocoon production and serves to protect larvae from adverse environmental conditions or predators. Species in the Sa...Insects produce silk for a range of purposes. In the Lepidoptera, silk is utilized as a material for cocoon production and serves to protect larvae from adverse environmental conditions or predators. Species in the Saturniidae family produce an especially wide variety of cocoons, for example, large, golden colored cocoons and those with many small holes. Although gene expression in the silk gland of the domestic silkworm （Bombyx mori L.） has been extensively studied, considerably fewer investigations have focused on members of the saturniid family. Here, we established expression sequence tags from the silk gland of the eri silkworm （Samia ricini）, a saturniid species, and used these to analyze gene expression. Although we identified thefibroin heavy chain gene in the established library, genes for other major silk proteins, such asfibroin light chain andfibrohexamerin, were absent. This finding is consistent with previous reports that these latter proteins are lacking in saturniid silk. Recently, a series offibrohexamerin-like genes were identified in the Bombyx genome. We used this information to conduct a detailed analysis of the library established here. This analysis identified putative homologues of these genes. We also found several genes encoding small silk protein molecules that are also present in the silk of other Lepidoptera. Gene expression patterns were compared between eri and domestic silkworm, and both conserved and nonconserved expression patterns were identified for the tested genes. Such differential gene expression might be one of the major causes of the differences in silk properties between these species. We believe that our study can be of value as a basic catalogue for silk gland gene expression, which will yield to the further understanding of silk evolution.展开更多
文摘The bivoltine silkworm Bombyx mori （Lepidoptera： Bombycidae） exhibits a maternally controlled embryonic diapause. Maternal silkworms decide whether to lay diapause or nondiapause eggs depending on environmental factors such as the temperature and photoperiod during the egg and larval stages, and then induce diapause eggs during the pupal stage. However, little is known about the molecular mechanism that conveys the outcome of whether to produce diapause or nondiapause eggs from the egg or larval stages to the pupal stage. This study used microarray analysis to investigate differentially expressed genes in the larval brains of diapause- and nondiapause-egg producers, to which bivoltine silkworms were destined by thermal or photic stimulation during the egg stage. The cytochrome P450 18al and Kriippel homolog i genes were upregulated in producers of diapause eggs compared with those of nondiapause eggs under both experimental conditions. Cytochrome P450 18al encodes a key enzyme for steroid hormone inactivation and Krfippel homolog 1 is an early juvenile hormone-inducible gene that mediates the repression of metamorphosis. The upregulation of these genes during the larval stage might be involved in the signaling pathway that transmits information about the diapause program from the egg stage to the pupal stage in the silkworm.
文摘Insects produce silk for a range of purposes. In the Lepidoptera, silk is utilized as a material for cocoon production and serves to protect larvae from adverse environmental conditions or predators. Species in the Saturniidae family produce an especially wide variety of cocoons, for example, large, golden colored cocoons and those with many small holes. Although gene expression in the silk gland of the domestic silkworm （Bombyx mori L.） has been extensively studied, considerably fewer investigations have focused on members of the saturniid family. Here, we established expression sequence tags from the silk gland of the eri silkworm （Samia ricini）, a saturniid species, and used these to analyze gene expression. Although we identified thefibroin heavy chain gene in the established library, genes for other major silk proteins, such asfibroin light chain andfibrohexamerin, were absent. This finding is consistent with previous reports that these latter proteins are lacking in saturniid silk. Recently, a series offibrohexamerin-like genes were identified in the Bombyx genome. We used this information to conduct a detailed analysis of the library established here. This analysis identified putative homologues of these genes. We also found several genes encoding small silk protein molecules that are also present in the silk of other Lepidoptera. Gene expression patterns were compared between eri and domestic silkworm, and both conserved and nonconserved expression patterns were identified for the tested genes. Such differential gene expression might be one of the major causes of the differences in silk properties between these species. We believe that our study can be of value as a basic catalogue for silk gland gene expression, which will yield to the further understanding of silk evolution.
