Fig. 2: The Y chromosome affects heterochromatin loci in trans, in proportion to its size.
From: Y chromosome toxicity does not contribute to sex-specific differences in longevity
a–c, Effects of Y chromosome size on the expression of the white-based heterochromatin reporters wm4 in XXY females (a), w118E-25 in males (b) and w118E-10 in males (c). Red eye-pigment levels were determined by measuring absorbance at 480 nm. R2 from nonlinear regressions, using sigmoidal dose–response equations. d, Representative pictures comparing wm4 reporter expression in XY and X0 males carrying two (control), three (gain-of-function) or one (loss-of-function) copies of the Su(var)3-9 gene. e, Effect of Y chromosome size on the expression of the wm4 reporter in males missing one copy of HP1. P value and R2 from simple linear regression, ***P < 0.0001. f, When the white (w) gene is artificially translocated in the constitutive heterochromatin (dark blue), the presence of a Y chromosome sequesters key factors, like HP1, allowing w expression and red-eye phenotype (on the right). Reduction of Y size, here by a factor of five (with Y21), releases HP1 proteins and triggers w cis-heterochromatin inactivation giving a white-eye phenotype (on the left). In all panels, n = number of repeats (each repeat containing five flies). Scale bars, 50 μm. See also Extended Data Fig. 2.
