The amount of heterochromatic proteins in the egg is correlated with sex determination in <Emphasis Type="Italic">Planococcus citri</Emphasis> (Homoptera,Coccoidea) |
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Authors: | Giovanni Luigi Buglia Daniela Dionisi Marina Ferraro |
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Institution: | (1) Department of Genetics and Molecular Biology, University of Rome “La Sapienza”, P.le A. Moro 5, 00185 Rome, Italy; |
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Abstract: | In the mealybug Planococcus citri, there are no identifiable sex chromosomes. Early in the development of embryos destined to become males, the genome contributed
by the sperm undergoes heterochromatization and, following an inverted type of meiosis, will be eliminated. Only two vital
sperms are therefore produced, both carrying the same maternally derived genome. A differential distribution observed on the
two spermatids during male germline cyst formation of chromatin remodeling factors such as HP1 and methylated K9 histone H3
prompted us to propose an imprinting/sex determination model in which the imprinted sperm is the one to undergo heterochromatization
at syngamy. The sex ratio is normally 1:1, but aged females are known to produce almost exclusively male progeny, suggesting
that the imprinting pattern of the male gamete in P. citri, though necessary, is apparently not sufficient for sex determination. We report here that egg cells of aged females show
larger amounts of HP1 and Su(Var)3–9 than egg cells of young females. These data suggest that a determinant of sex may be
the amount of maternally derived heterochromatic proteins. |
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