Biology subjects

Takasu, Y.

Publications and source records attributed to Takasu, Y..

3 recordsLinked to original sources

bioRxiv2025

An ATP-binding cassette subfamily C is crucial for flavonoid sequestration in the domestic silkworm, Bombyx mori

Some herbivorous insects have evolved sequestration mechanisms, the ability to take up and accumulate plant secondary metabolites for their own benefit. The domestic silkworm, Bombyx mori, and its wild ancestor, B. mandarina, take up flavonoids from mulberry leaves and accumulate the molecules as their glucosides in their tissues and cocoon shell. This sequestration enhances the cocoons protective property against ultraviolet or bacterial proliferation. Here, we show that an ATP-binding cassette transporter subfamily C (ABCC) gene, BmABCC4, plays a crucial role in the flavonoid sequestration in the silkworms. BmABCC4 is located at Green c, a cocoon color-associated locus predicted in 1941 and whose detailed position we previously identified. This transporter is expressed in the midgut and silk glands, and the expression is upregulated in the midgut in late period of final instar larva. Knockout of BmABCC4 significantly reduced the total flavonoid content in the tissues and cocoon shell. Our results suggest that BmABCC4 transports flavonoid glucosides from the midgut cells to hemolymph and from the silk gland cells to the silk gland lumen.

genetics↗

bioRxiv2023

A novel monocarboxylate transporter involved in 3-hydroxykynurenine transport for ommochrome coloration

Ommochromes are widespread pigments in invertebrates utilized for screening pigments in compound eyes and for reddish coloration in epidermis and wings. Ommochromes are derived from 3-hydroxykynurenine (3OHK), which is incorporated into cells from hemolymph or synthesized from tryptophan within cells. While the synthetic pathway from tryptophan to 3OHK has been well characterized, the gene responsible for cellular uptake of 3OHK has been poorly understood. In the silkworm Bombyx mori, adult compound eyes and eggs contain a mixture of ommochrome pigments. By using positional cloning method, we found that a novel monocarboxylate transporter, 3-hydroxykynurenine transporter (3OHKT), is responsible for the recessive mutant maternal brown of Tsujita (b-t) of B. mori. In b-t mutant, the color of the eggs is light brown, whereas the color of the compound eyes is normal, and we identified a 2-kb deletion in 3OHKT gene. TALEN-mediated knockout of 3OHKT gene produced the same coloration phenotype as b-t mutant, and the complementation test between b-t mutant and 3OHKT knockout strain proved that 3OHKT is responsible for b-t phenotype. 3OHKT protein was localized in the cellular membrane, and LC-MS analysis indicated that the uptake of 3OHK from hemolymph into the ovary was suppressed in the b-t mutant. Moreover, we confirmed that 3OHKT gene is specifically expressed at the reddish region and the time of pigmentation in the pupal wing of nymphalid butterflies. RNA interference of 3OHKT prevented reddish pigmentation in wings, highlighting its general involvement in ommochrome-based pigmentation other than compound eyes. SignificanceOmmochromes are widely distributed pigments in invertebrates and are synthesized from intracellular tryptophan or 3-hydroxykynurenine (3OHK). Ommochrome-based red markings on butterfly wings are often used for sexual selection, warning colors and mimicry. Most genes involved in the ommochrome synthesis pathway have been elucidated from analyses of eye color mutants in Drosophila. However, this study reveals that the ommochrome synthesis pathway has a different genetic repertoire depending on the tissues, and that the novel monocarboxylate transporter identified in this study has a major role in ommochrome pigmentation other than in compound eyes. In particular, our results suggest that classical ommochrome-related genes are rarely involved in the wing pigmentation of the nymphalid butterflies.

genetics↗

bioRxiv2022

Differential requirement of nanos homologs in the germline suggests the evolutionary path toward an inheritance mechanism of primordial germ cell formation in the silkmoth Bombyx

The lepidopteran insect Bombyx mori possesses unique embryogenesis characteristics among insects. nanos (nos) has conserved functions in metazoan primordial germ cell formation. Bombyx possesses four nos genes (M, N, O, P), a unique feature found in lepidopterans examined so far. Of these, maternal nosO mRNA exhibits a localization pattern: it may act as a primordial germ cell (PGC) determinant. A previous knock-out experiment of nosO showed that this localized mRNA is dispensable for PGC formation in laboratory environment and has limited involvement in PGC specification. This study examined whether other nos genes act redundantly with nosO in germline using RNAi and gene editing. Although individual embryonic RNAi exhibited no detectable phenotypic alterations, simultaneous RNAi of nosO/ nosP markedly reduced oocyte number and male fecundity. Additionally, nosP KO almost completely sterilized both sexes. Because nosP is broadly expressed in the posterior of embryos in non-germline specific manner, these results could reflect an evolutionary step taken by Bombyx toward its unique inheritance mechanisms. This study also suggests that nos genes in Bombyx do not affect anterior-posterior axis specification. This could reflect its characteristic embryogenesis.

developmental biology↗