Loss-of-function alleles of the JIL-1 histone H3S10 kinase enhance position-effect variegation at pericentric sites in Drosophila heterochromatin

Abstract

In this study we show that loss-of-function alleles of the JIL-1 histone H3S10 kinase act as enhancers of position-effect variegation at pericentric sites whereas the gain-of-function JIL-1(Su(var)3-1[3]) allele acts as a suppressor strongly supporting a functional role for JIL-1 in maintaining euchromatic chromatin and counteracting heterochromatic spreading and gene silencing.

Figure 1.—

The effect of JIL-1 loss-of-function alleles and the gain-of-function JIL-1^{Su(var)3-1[3]} allele on PEV of the P-element lines 118E-10, 118E-25, 118E-32, and 39C-3, which were inserted into pericentric heterochromatin. (Top) PEV in the eyes of control flies with a wild-type JIL-1 allele (+/+). (Middle) A hypomorphic allelic combination of the JIL-1 alleles JIL-1^z60 (z60) and JIL-1^z2 (z2) leads to a strong enhancement of PEV as indicated by the nearly completely white eye phenotype. (Bottom) In contrast, the homozygous gain-of-function JIL-1^{Su(var)3-1[3]} allele (3-1/3-1) leads to strong suppression of PEV as indicated by the nearly completely red eye phenotype. All images are from female flies. Drosophila melanogaster fly stocks were maintained according to standard protocols (Roberts 1998). Canton-S was used for wild-type preparations. The JIL-1^z2 and JIL-1^z60 alleles are described in Wang et al. (2001) and in Zhang et al. (2003). The JIL-1^{Su(var)3-1[3]}/TM3 Sb Ser stock was obtained from the Bloomington Stock Center. Balancer chromosomes and markers are described in Lindsley and Zimm (1992). Strains containing X chromosomes with the w¹¹¹⁸ allele and a loss-of-function JIL-1 allele (either JIL-1^z2 or JIL-1^z60) or the gain-of-function JIL-1^{Su(var)3-1[3]} allele heterozygous with the TM6 Sb Tb e third chromosome balancer were produced by standard crossing. Subsequent crosses between these strains generated flies with different JIL-1 allelic combinations in a background homozygous for P[hsp26-pt, hsp70-w] insertions that were introduced from the P-element lines 118E-10, 118E-25, 118E-32, or 39C-3 (Wallrath and Elgin 1995; Wallrath et al. 1996; Cryderman et al. 1998) by standard crosses. As a control, PEV of each of these transgenes was analyzed in flies homozygous for a Canton-S wild-type third chromosome. The hsp70 promoter is leaky and promotes sufficient expression to generate a variegated eye phenotype under non-heat-shock conditions (Wallrath and Elgin 1995). To quantify the variegated phenotype, newly eclosed adults were collected, aged for 4–5 days at 25°, and then sorted into different classes on the basis of the percentage of the eye that was red. Eyes from representative individuals from these crosses were photographed using an Olympus stereo microscope and a Spot digital camera (Diagnostic Instruments).

Figure 2.—

JIL-1 loss-of-function alleles and the gain-of-function JIL-1^{Su(var)3-1[3]} allele affect the distribution of the percentage of red ommatidia in female flies homozygous for the P-element lines 118E-10, 118E-25, 118E-32, and 39C-3, which were inserted into pericentric heterochromatin. In the histograms the eyes from wild-type JIL-1 flies (wt), homozygous JIL-1^z60 flies (z60/z60), JIL-1^z2/JIL-1^z60 flies (z2/z60), and JIL-1^{Su(var)3-1[3]}/JIL-1^{Su(var)3-1[3]} flies (3-1/3-1) were sorted into different classes on the basis of the percentage of the eye that was red. The data suggest that for each P-element insertion line PEV is enhanced by JIL-1 loss-of-function alleles as indicated by the increased proportion of white ommatidia whereas PEV is suppressed by the gain-of-function JIL-1^{Su(var)3-1[3]} allele as indicated by the increased proportion of red ommatidia.