Dosage Analysis Of Z Chromosome Genes In Silkworm, Bombyx Mori

Dosage compensation effect is a genetic effect in sex determination mechanism of male-heterogametic species,which making the level of most sex-linked gene products equal in two sexes.In some species,such as mammals,Drosophila melanogaster, Caenorhabditis elegans,etc.the mechanism of dosage compensation has been studied throughly up to now.However,we learned little about the molecular basis of the mechanism of dosage compensation in Bombyx mori.Studies on the mechanism of dosage compensation is an important part for us to reveal the mechanism of the sex determination in Bombyx mori.In this research work, we performed a dosage analysis of Z chromosome in Bombyx mori by using microassay. We summaried the results we got as following:1.Five hundred seventy nine genes which locate on the Z chromosome have been identified.Using these identified genes as queries,a further BLAST search have been performed with the protein sequence data in GenBank.The results indicate that 547 of the identified genes have homologues in the database,while 32 genes have no homologues.There are 490 genes with gene function annotation.Most of these genes function as binding proteins,catalytic protein and transporters,etc.2.RNAs of different tissues and organs of Dazao including anterior/median silk gland(A/MSG),testis,ovary,integument,malpighian tubule,and head were isolated seperately from female and male larvae on day 3 of the fifth instar.RNA samples were purified and subsequently used in the next step.Gene expression patterns of the 12 above samples have surveyed by genome-wide microarray.For tissue or organ testis, ovary,head of the female,and anterior/median silk gland(A/MSG)of the female,three biological repeats have been carried out,while 2 and 4 biological repeates for integument of the female and malpighian tubule of the female,respectively.Each experiment was performed as a dye-swap.The results of the microarray indicate that among the genes locating on the Z chromosome,there are 314,180,186,155,132 expressed in the gonad,integument,head,malpighian tubule and anterior/median silk gland(A/MSG)respectively.3.We detected 579 genes on Z chromosome with different expression profiles,Of which,314 genes were expressed in gonads,180 genes in integuments,186 genes in heads,155 genes in Malpighian tubules,and 132 genes in anterior/median silk glands. Male:female(M:F)ratios of expression of genes on Z chromosome were calculated.In gonad,78%of 314 active genes expressed with a M:F ratio value more than 1,and 90% of 180 genes in integument,85%of 186 in head,74%of 155 in malpighian tubule,and 65%of 132 in A/MSG.The mass proportion of genes was with ratio value more than 1. The results showed that the Z chromosome gene expression level in male and female in various tissues or organs have reached a significant difference.The silkworm is female heterohomozygous(male ZZ,femal ZW).Silkworm Z chromosome gene expression in males was significantly higher than that of females.That is,silkworm body does not eliminate differences of the expression between male and female as a result of different number of chromosomes.There is no dosage compensation in silkworm.4.Functional analysis of Z-linked genes was sorted by M:F ratios.To compare sets of different expression genes in sexes,we classified Z-linked genes into three categories by M:F ratios:male-biased genes(M:F≥1.5),female-biased genes(M:F＜0.5)and no-biased genes(M:F 0.8-1.2).In somatic tissues,there were 94 male-biased genes,57 no-biased genes,and 6 female-biased genes.The male-biased genes were enriched for binding activity,catalytic activity,transport,transtription regulation,molecular transduction,antioxidant activity,enzyme regulation and motor,which probably reflect some silkworm sex-linked characters.5.We detected the distribution of region of M:F on the Z chromosome,the results showed that M:F value randomly distribute on Z chromosomes.Male-biased, female-biased or unbiased genes are not concentrated in a particular region of Z chromosome.6.Correlation analysis of M:F ratio and the expression of genes,we found male-biased genes showed low expression,but no-biased genes had higher one.On Z chromosome,the ratio of M:F is to a certainity related with the gene expression.In this study,we tested the expression of Z chromosome genes.The results suggested there are no dosage compensation in silkworm,and that M:F value is no correlated to Z chromosome sequence itself,but to their expresion level.The results is of great significance for us to study silkworm Z chromosome and improve our knowledge of sex-determining network.