A <i>mdg4</i> Retrotransposon Screen for X-linked Female Sterile Alleles and its Relationship with the Transcription Factor OVO

In the germline, the <i>mdg4</i> retrotransposon integrates in close proximity to the location of OVO DNA binding motifs, suggesting that insertion bias is driven by the OVO transcription factor. A classical genetic example of this is the reversion of the dominant female-sterile allele, <i>ovo</i> ^<i>D1</i> , by the transposition of <i>mdg4</i> into the <i>ovo</i> promoter where OVO protein binds. We wanted to take advantage of this relationship and determine if we could recover female sterile alleles along the X chromosome due to <i>mdg4</i> insertion, with the hypothesis that these would be genes that OVO binds and transcriptionally regulates in the germline. We mobilized the <i>mdg4</i> retrotransposon with the use of mutants for the lncRNA gene <i>flamenco</i> (<i>flam)</i> and recovered 17 recessive female sterile alleles out of a total of 1,192 chromosomes screened. We identified 11 complementation groups, for which a <i>mdg4</i> insertion was responsible for female sterility in 7 groups. Notably, a complementation group consisting of 6 alleles was found to be the result of a <i>Doc</i> transposable element insertion into the gene <i>Grip91</i> and is potentially evidence for a <i>Doc</i> insertional 'hotspot' in the genome. Our screen also uncovered that 7/17 recessive female sterile chromosomes contained multiple transposable element insertions indicating that <i>flam</i> ^- females derepress numerous transposable elements that can lead to multiple transposon insertions along a single chromosome, as has been suggested previously. Altogether, we found that <i>mdg4</i> did have an insertion bias into OVO bound regions of the genome that can result in female sterility, however, this was the case for a minority of the female sterile alleles recovered with this method.