Distribution of heterochromatin on the mitotic chromosomes of Musca domestica L. in relation to the activity of male-determining factors.
In the housefly, male sex is determined by a dominant factor, M, located either on the Y, on the X, or on any of the five autosomes. M factors on autosome I and on fragments of the Y chromosome show incomplete expressivity, whereas M factors on the other autosomes are fully expressive. To test whether these differences might be caused by heterochromatin-dependent position effects, we studied the distribution of heterochromatin on the mitotic chromosomes by C-banding and by fluorescence in situ hybridization of DNA fragments amplified from microdissected mitotic chromosomes. Our results show a correlation between the chromosomal position of M and the strength of its male-determining activity: weakly masculinizing M factors are exclusively located on chromosomes with extensive heterochromatic regions, i.e., on autosome I and on the Y chromosome. The Y is known to contain at least two copies of the M factor, which ensures a strong masculinizing effect despite the heterochromatic environment. The heterochromatic regions of the sex chromosomes consist of repetitive sequences that are unique to the X and the Y, whereas their euchromatic parts contain sequences that are ubiquitously found in the euchromatin of all chromosomes of the complement.
Hediger
M
M
Institute of Zoology, University of Zürich-Irchel, CH-8057 Zürich, Switzerland.
Niessen
M
M
Müller-Navia
J
J
Nöthiger
R
R
Dübendorfer
A
A
D000818:Animals; D002871:Chromosome Banding; D002875:Chromosomes / Q000235:genetics / Q000648:ultrastructure*; D004251:DNA Transposable Elements; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006570:Heterochromatin / Q000502:physiology*; D006793:Houseflies / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008938:Mitosis; D016133:Polymerase Chain Reaction; D012730:Sex Chromosomes / Q000235:genetics / Q000648:ultrastructure; D019849:Sex Determination Processes
D004251:DNA Transposable Elements; D006570:Heterochromatin