Taming active transposons at Drosophila telomeres: The interconnection between HipHop’s roles in capping and transcriptional silencing
Fig 9
A speculative model for the intricate relationship between the capping and silencing functions of the capping machinery.
The scale in the center represents the strengths of various hiphop mutant combinations from “null” to “wt”, with the deduced positions indicated for the hiphopHA/HA and the hiphopHA/df allelic combinations. The capping and silencing functions are shown to either side of the center scale as two horizontal scales. For the capping function, two thresholds of functional requirements have been identified: one for capping in early embryos that are controlled by the maternal hiphop genotype, and the other for capping during somatic development. For the silencing function, a continuous decline correlates with the strengths of different mutations. It is defined as lost (reaching zero) when viability of the mutants is no longer supported due to somatic uncapping. Depending on which function is more sensitive to the partial loss of HipHop functions, separation-of-function mutations would have different properties. This model assumes that the silencing function has a lower threshold of producing mutant phenotypes than one for capping.