A correlation between development time and variegated position effect inDrosophila melanogaster

Abstract

SummaryPosition-effect variegation is a phenomenon in which cell-autonomous genes, normally expressed in all cells of a tissue, are expressed in some cells but not in others, leading to a mosaic tissue. Variegation occurs when a normally euchromatic gene is re-positioned close to heterochromatin by chromosome rearrangement. The extent of variegation is known to be influenced by a number of environmental and genetic factors. In the courss of investigations of the influence of the pH of larval medium on the extent of eye-colour variegation in In(1)ωm4 Drosophila melanogaster, we have found that the extent of variegation depends on development time. Flies reared at pH 2·6 develop slowly and show more extreme variegation than those reared at higher pH. This effect, as well as variations within the pH treatments, can be accounted for by differences in development time. The observed regression relationship between variegation and development time also appears to accommodate the influences of temperature on both variables. We suggest that development time may account causally for the reported influences of a number of environmental agents (temperature, crowding, chemicals) on variegation. Ways in which this might occur are discussed in the context of models of the molecular basis of differential gene activity.

Acf1 confers unique activities to ACF/CHRAC and promotes the formation rather than disruption of chromatin in vivo

“…For instance, mutations or environmental conditions (temperature, crowding, chemicals) that lead to a developmental delay have been observed to enhance variegation (Michailidis et al 1988). Although the pupal development of homozygous acf1 flies is delayed relative to that of their wild-type counterparts, we observe suppression rather than enhancement of PEV on mutation of acf1.…”

Developmental timing and tissue specificity of heterochromatin-mediated silencing.

“…In addition, because reactivation takes place after the cessation of mitosis, it appears that heterochromatic silencing in Drosophila can be reversed without the cell cycle, which, however, is a prerequisite for the metastability of epigenetically silenced loci in yeast (Pillus and Rine, 1989;Gottschling et al, 1990). However, while these temperature studies may have tested the same mechanism that we have uncovered, they also perturb other temperature-dependent processes such as stress response and the length of development, which are known to modify PEV (Michailidis et al, 1988). However, while these temperature studies may have tested the same mechanism that we have uncovered, they also perturb other temperature-dependent processes such as stress response and the length of development, which are known to modify PEV (Michailidis et al, 1988).…”

“…Finally, it is interesting that reactivation of the transgene occurs within a putative temperature-sensitive period (Spofford, 1976) for white variegation. However, while these temperature studies may have tested the same mechanism that we have uncovered, they also perturb other temperature-dependent processes such as stress response and the length of development, which are known to modify PEV (Michailidis et al, 1988). In contrast, our system has minimized these variables and sought to detect developmental switches within the naturally programed course of heterochromatic silencing.…”

Epigenetic silencing of a foreign gene in nuclear transformants of Chlamydomonas.

“…In Drosophila, euchromatic genes subject to PEV are frequently responsive to temperature. At low temperatures, there is greater repression of gene expression (i.e., enhancement of variegation) (Spofford, 1976;Michailidis et al, 1988).…”

“…The survival on spectinomycin of Chlamydomonas transformants was sensitive to temperature, with lower temperatures reducing the survival and presumably the level of chimeric gene expression. (Heter0)chromatin-mediated variegated gene expression in Drosophila and fission yeast is similarly affected by temperature (Spofford, 1976;Michailidis et al, 1988;Allshire et al, 1994). As mentioned above, intermediate levels of expression in individual cells, resembling our observations in Chlamydomonas, have been reported for transgenes inserted at centromeres in S. pombe (Allshire et al, 1994).…”