Mapping and recombination analysis of two moth colour mutations, Black moth and Wild wing spot, in the silkworm Bombyx mori

Abstract

Many lepidopteran insects exhibit body colour variations, where the high phenotypic diversity observed in the wings and bodies of adults provides opportunities for studying adaptive morphological evolution. In the silkworm Bombyx mori, two genes responsible for moth colour mutation, Bm and Ws, have been mapped to 0.0 and 14.7 cM of the B. mori genetic linkage group 17; however, these genes have not been identified at the molecular level. We performed positional cloning of both genes to elucidate the molecular mechanisms that underlie the moth wing-and body-colour patterns in B. mori. We successfully narrowed down Bm and Ws to~2-Mb-long and 100-kb-long regions on the same scaffold Bm_scaf33. Gene prediction analysis of this region identified 77 candidate genes in the Bm region, whereas there were no candidate genes in the Ws region. Fluorescence in-situ hybridisation analysis in Bm mutant detected chromosome inversion, which explains why there are no recombination in the corresponding region. The comparative genomic analysis demonstrated that the candidate regions of both genes shared synteny with a region associated with wing-and body-colour variations in other lepidopteran species including Biston betularia and Heliconius butterflies. These results suggest that the genes responsible for wing and body colour in B. mori may be associated with similar genes in other Lepidoptera.

The industrial melanism mutation in British peppered moths is a transposable element

“…Expression of alternative candidate genes. Two B. mori adult melanism/patterning mutations, Black moth (Bm) and Wild wing spot (Ws), were recently mapped to a region partially orthologous to the carbonaria interval 21 . In this study, end-point PCR showed complete absence of cortex expression in pupal stages and adults but potentially important prepupal stages were not examined.…”

Comparative Analysis of Transcriptomes among Bombyx mori Strains and Sexes Reveals the Genes Regulating Melanic Morph and the Related Phenotypes

“…Functional defects or abnormal expression of some key genes in the melanin metabolism pathway can also lead to melanism [ 6 , 9 , 10 ]. In contrast, some studies found that some melanic morphs had no variations in the classic melanin metabolism pathway genes indicating the mechanistic diversity of melanism [ 7 , 11 , 12 ]. An example for this mechanism is the industrial melanism in the peppered moth ( Biston betularia ) [ 7 , 11 ].…”

“…The silkworm, Bombyx mori , is the most advanced lepidopteran model with over 100 body color mutants described thus far [ 19 , 20 ]. Studies of body color mutants has enhanced our fundamental understanding of the silkworm pigmentation processes and the genetic mechanisms underlying insect melanism [ 6 , 10 , 12 , 21 – 25 ].…”

From Patterning Genes to Process: Unraveling the Gene Regulatory Networks That Pattern Heliconius Wings

“…In Heliconius, the locus acts across both wing surfaces and underlies variation in white, yellow, orange, and black pattern elements (Joron et al, 2006). Cortex has also been implicated in pattern variation in other butterflies (VanKuren et al, 2019), the peppered moth Biston betularia and other geometrids (van't Hof et al, 2016(van't Hof et al, , 2019, as well as the silkmoth Bombyx mori (Ito et al, 2016). Secondly, nearly all the patterning genes thus far identified are highly conserved at the amino acid level and are used extensively throughout embryonic and larval development, and later simply redeployed on a developing wing to affect pattern variation.…”