Fig. 5. Mutations in the genes encoding the U2AF38 and U1-70K splicing factors are dosage-sensitive maternal modifiers of Sxl splicing autoregulation. (A) Synergistic genetic interactions between splicing factors leads to female-lethality. In these assays females of the indicated maternal genotype were mated to Sxl^7BO/Y males and the resulting male and female progeny scored. The viability of the female progeny, all of which are heterozygous for Sxl (Sxl^7B0/+), was assessed by comparing the number of females recovered to the number of males recovered. (B) Sxl splicing pattern in Sxl^7B0/+ female embryos. Splicing was assayed by an RT-PCR based assay, in which RNA was isolated from a pool of embryos in which only the Sxl^7B0/+ embryos carried the reporter construct. This pool of embryos was collected from the experimental adult females crossed to males carrying an X-chromosome which carries both Sxl^7B0 and a copy of the Sxl reporter construct described in Fig. 3E. Lanes 3-5: embryos were collected from snf^J210/+ control mothers (lane 3); snf^J210/+; U2af38^E18/+ mothers (lane 4); and snf^J210/+; U1-70K¹/+ mothers (lane 5). Controls include: lane 1, splicing of the reporter construct in adult males; and lane 2, splicing of the reporter construct in adult females.