Transcriptomic analysis at the first instar larval stage of nonmolting Bombyx mori mutant (a42).

The life cycle of the holometabolous insect Bombyx mori (Linnaeus) consists of the embryo, larva, pupa, and adult stages with six larval molts. Ecdysone and juvenile hormones play important roles in the growth and development of the silkworms. The a42 silkworm mutant is recessive and homozygous lethal by exhibiting a dark-colored and small body size and fails to molt to second instar. We compared the gene expression of a42 mutants with normal individuals at the first larval molting stage to elucidate the physiological influence of the a42 mutation on the growth and development of silkworms. The transcriptomic sequencing results revealed that 1,411 genes are differentially expressed in a42 mutants, compared with wild-type control silkworms, in which 791 genes are upregulated and 620 genes are downregulated. Gene Ontology/Kyoto Encyclopedia of Genes and Genomes analyses identified differentially expressed genes (DEGs) assigned to biological pathways, such as pentose and glucoronate interconversions, glycerolipid metabolism, folate biosynthesis, amino sugar, and nucleotide sugar metabolism. Two hydroxylases of phenylalanine hydroxylase (BmPAH) and tyrosine hydroxylase (BmTh) are upregulated in a42 mutants. The influence of a42 mutation on these DEGs reveals that melanin metabolism plays an important role during the molting process in silkworms.