# The Tofu Mutation Restores Female Fertility to Drosophila with a Null BEAF Mutation

## TL;DR

A mutation called Tofu helps female fruit flies regain fertility when they lack a specific protein called BEAF, which is important for egg production.

## Contribution

The study identifies a compensatory mutation, Tofu, that rescues fertility in Drosophila lacking BEAF, suggesting a functional link between BEAF and the rib gene.

## Key findings

- Tofu is a dominant mutation that rescues the defective ovary phenotype caused by null BEAF alleles.
- Tofu likely involves a mutation in a Polycomb response element upstream of the ribbon gene, leading to aberrant rib expression.
- BEAF and Rib colocalize at promoters, indicating potential overlap in gene regulation.

## Abstract

Background: Compensatory mutations offer clues in deciphering the role of a particular protein in cellular processes. Here, we investigate an unknown compensatory mutation, present in the BEAFNP6377 fly line, that provides sufficient rescue of the defective ovary phenotype caused by null BEAF alleles to allow the maintenance of fly stocks lacking the chromatin domain insulator proteins Boundary Element-Associated Factors BEAF-32A and BEAF-32B. We call this dominant mutation Tofu. Methods: We employ both classical genetics and genomic sequencing to attempt to identify the mutation. Results: We find evidence that points to a mutation in a predicted Polycomb response element (PRE) upstream of the ribbon transcription factor gene. This may lead to aberrant rib expression, which is otherwise not expressed in adult ovaries. BEAF and Rib colocalize to a set of promoters, suggesting overlap in gene regulation. Conclusions: Tofu could be a PRE mutation leading to the aberrant activation of rib in the ovaries. This could allow Rib to compensate for a lack of BEAF to activate one or more coregulated genes necessary for egg production in flies.