Partial deletions of the W chromosome due to reciprocal translocation in the silkworm Bombyx mori.
In the silkworm, Bombyx mori (female, ZW; male, ZZ), femaleness is determined by the presence of a single W chromosome, irrespective of the number of autosomes or Z chromosomes. The W chromosome is devoid of functional genes, except the putative female-determining gene (Fem). However, there are strains in which chromosomal fragments containing autosomal markers have been translocated on to W. In this study, we analysed the W chromosomal regions of the Zebra-W strain (T(W;3)Ze chromosome) and the Black-egg-W strain (T(W;10)+(w-2) chromosome) at the molecular level. Initially, we undertook a project to identify W-specific RAPD markers, in addition to the three already established W-specific RAPD markers (W-Kabuki, W-Samurai and W-Kamikaze). Following the screening of 3648 arbitrary 10-mer primers, we obtained nine W-specific RAPD marker sequences (W-Bonsai, W-Mikan, W-Musashi, W-Rikishi, W-Sakura, W-Sasuke, W-Yukemuri-L, W-Yukemuri-S and BMC1-Kabuki), almost all of which contained the border regions of retrotransposons, namely portions of nested retrotransposons. We confirmed the presence of eleven out of twelve W-specific RAPD markers in the normal W chromosomes of twenty-five silkworm strains maintained in Japan. These results indicate that the W chromosomes of the strains in Japan are almost identical in type. The Zebra-W strain (T(W;3)Ze chromosome) lacked the W-Samurai and W-Mikan RAPD markers and the Black-egg-W strain (T(W;10)+(w-2) chromosome) lacked the W-Mikan RAPD marker. These results strongly indicate that the regions containing the W-Samurai and W-Mikan RAPD markers or the W-Mikan RAPD marker were deleted in the T(W;3)Ze and T(W;10)+(w-2) chromosomes, respectively, due to reciprocal translocation between the W chromosome and the autosome. This deletion apparently does not affect the expression of Fem; therefore, this deleted region of the W chromosome does not contain the putative Fem gene.
Abe
H
H
Department of Biological Production, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Japan. wfem@cc.tuat.ac.jp
Seki
M
M
Ohbayashi
F
F
Tanaka
N
N
Yamashita
J
J
Fujii
T
T
Yokoyama
T
T
Takahashi
M
M
Banno
Y
Y
Sahara
K
K
Yoshido
A
A
Ihara
J
J
Yasukochi
Y
Y
Mita
K
K
Ajimura
M
M
Suzuki
M G
MG
Oshiki
T
T
Shimada
T
T
D000818:Animals; D001483:Base Sequence; D012831:Bombyx / Q000235:genetics*; D002872:Chromosome Deletion; D022202:Chromosomes, Artificial, Bacterial; D004247:DNA / Q000737:chemistry / Q000235:genetics; D005260:Female; D015723:Gene Library; D005819:Genetic Markers; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008969:Molecular Sequence Data; D019105:Random Amplified Polymorphic DNA Technique; D018626:Retroelements / Q000235:genetics; D012729:Sex Chromosome Aberrations; D012730:Sex Chromosomes / Q000235:genetics*; D014178:Translocation, Genetic / Q000235:genetics*
D005819:Genetic Markers; D018626:Retroelements; D004247:DNA