Identification of the female-determining region of the W chromosome in Bombyx mori.
The W chromosome of the silkworm Bombyx mori is devoid of functional genes, except for the putative female-determining gene (Fem). To localize Fem, we investigated the presence of W-specific DNA markers on strains in which an autosomal fragment containing dominant marker genes was attached to the W chromosome. We produced new W-chromosomal fragments from the existing Zebra-W strain (T(W;3)Ze chromosome) by X-irradiation, and then carried out deletion mapping of these and sex-limited yellow cocoon strains (T(W;2)Y-Chu, -Abe and -Ban types) from different Japanese stock centers. Of 12 RAPD markers identified in the normal W chromosomes of most silkworm strains in Japan, the newly irradiated W(B-YL-YS)Ze chromosome contained three, the T(W;2)Y-Chu chromosome contained six, and the T(W;2)Y-Abe and -Ban chromosomes contained only one (W-Rikishi). To investigate the ability of the reduced W-chromosome translocation fragments to form heterochromatin bodies, which are found in nuclei of normal adult female sucking stomachs, we examined cells of the normal type p50 strain and the T(W;2)Y-Chu and -Abe strains. A single sex heterochromatin body was found in nuclei of p50 females, whereas we detected only small sex heterochromatin bodies in the T(W;2)Y-Chu strain and no sex heterochromatin body in the T(W;2)Y-Abe strain. Since adult females of all strains were normal and fertile, we conclude that only extremely limited region, containing the W-Rikishi RAPD sequence of the W chromosome, is required to determine femaleness. Based on a comparison of the normal W-chromosome and 7 translocation and W-deletion strains we present a map of Fem relative to the 12 W-specific RAPD markers.
Abe
H
H
Department of Biological Production, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Saiwai-cho, 3-5-8 Fuchu, Tokyo 183-8509, Japan. wfem@cc.tuat.ac.jp
Fujii
T
T
Tanaka
N
N
Yokoyama
T
T
Kakehashi
H
H
Ajimura
M
M
Mita
K
K
Banno
Y
Y
Yasukochi
Y
Y
Oshiki
T
T
Nenoi
M
M
Ishikawa
T
T
Shimada
T
T
D000818:Animals; D012831:Bombyx / Q000235:genetics*; D019457:Chromosome Breakage / Q000528:radiation effects; D022202:Chromosomes, Artificial, Bacterial / Q000235:genetics; D005260:Female; D005819:Genetic Markers / Q000235:genetics; D008297:Male; D008540:Meiosis / Q000235:genetics; D016133:Polymerase Chain Reaction; D019105:Random Amplified Polymorphic DNA Technique; D012730:Sex Chromosomes / Q000235:genetics*; D019849:Sex Determination Processes; D014965:X-Rays
D005819:Genetic Markers