[Mapping of non-lepis wing gene nlw in silkworm (Bombyx mori) using SSR and STS markers].

The non-lepis wing of silkworm (Bombyx mori) is controlled by the recessive gene, nlw. Owning to lack of crossing over in females, the reciprocal backcrossed F(1) (BC(1)) progenies were used for linkage analysis and mapping of nlw based on the SSR linkage map and STS markers using the wild type (+(nlw)/+(nlw)) silkworm strain P50 and U06 with scaleless wing (nlw/nlw). The nlw gene was linked to eight SSR markers and one STS marker. All the individuals with the wild type in the BC1F (Using F(1) as female to backcross to the recessive parent, that is (U06xP50)xU06) showed heterozygous profile of (U06xP50) F(1), and the ones with non-lepis wing in BC1F exhibited the homozygous profile of the strain U06. Using a reciprocal BC1M (Using F1 as male to backcross to the recessive parent, that is U06x(U06xP50))cross, we constructed a linkage map of 125.6 cM, and the distance between nlw and the nearest marker cash2p was 11.4 cM.

Differentially expressed genes in resistant and susceptible Bombyx mori strains infected with a densonucleosis virus.

We investigated variations in the gene expression of Bombyx mori following infection with a densonucleosis virus (BmDNV-Z). Two B. mori near-isogenic lines, Jingsong and Jingsong.nsd-Z.NIL, which are highly susceptible and completely resistant to BmDNV-Z, respectively, were used in this study. The infection profiles of BmDNV-Z in the midguts of the B. mori Jingsong and Jingsong.nsd-Z.NIL larvae revealed that the virus invaded the midguts of both of these strains. However, its proliferation was notably inhibited in the midgut of the resistant strain. By using the suppression subtractive hybridization method, three cDNA libraries were constructed to compare BmDNV-Z responsive gene expression between the two silkworm lines. In total, 151 differentially expressed genes were obtained. Real-time qPCR analysis confirmed that 11 genes were significantly up-regulated in the midgut of the Jingsong.nsd-Z.NIL strain following BmDNV-Z infection. Our results imply that these up-regulated genes might be involved in B. mori immune responses against BmDNV infection.

Inheritance and linkage analysis of co-dominant SSR markers on the Z chromosome of the silkworm (Bombyx mori L.).

Microsatellites or simple sequence repeats (SSRs) are co-dominant molecular markers. When we used fluorescent SSR markers to construct a linkage map for the female heterogametic silkworm (Bombyx mori, ZW), we found that some loci did not segregate in a Mendelian ratio of 1:1 in a backcross population. These loci segregated in a 3:1 ratio of single bands compared with double bands. Further examination of band patterns indicated that three types of SSR bands were present: two homozygotes and one heterozygote. In the beginning, we considered to discard these markers. By scoring male and female F1 individuals, we confirmed that these loci were located on the Z chromosome. Using the sex-linked visible mutation sch (K05) and its wild-type (C108), we constructed an F1 male backcross (BC1M) mapping population. The combination of sch backcross and SSR data enabled us to map the SSR markers to the Z chromosome. By adjusting input parameters based on these data, we were able to use Mapmaker software to construct a linkage map. This strategy takes advantage of co-dominant markers for positional cloning of genes on the Z chromosome. We localized sch to the Z chromosome relative to six SSR markers and one PCR marker, covering a total of 76.1 cM. The sch mutation is an important sex-linked visible mutation widely used in breeding of commercial silkworms (e.g. male silkworm selection rearing). Localization of the sch gene may prove helpful in cloning the gene and developing strains for marker-assisted selection in silkworm breeding.