At gastrulation, pit is expressed in the invaginating mesoderm . At this stage, all these territories are mitotically active and are programmed to enter into endoreplicative cycles. A strong expression is also observed in the anal plate. In late stages, expression becomes restricted to the differentiating midgut, the Malpighian tubules and the mesodermal sheath of gonads. However, this late expression is at a much lower level than that observed in the anterior and posterior midgut from stage 10-13 embryos.
Weak expression is also detectable in the epidermis at the end of embryogenesis.
Finally, pit is ubiquitously expressed in the imaginal discs . Polyclonal antibodies directed against the C-terminal half of Pitchoune do not resolve its subcellular localization. Transfected S2 Drosophila cells were heat shocked and processed for immunodetection. Since the function of Pit seemed to be required in the nucleolus, an eventual perturbation of this organelle was investigated in pit 10 mutant larvae. As a marker for the nucleolus, an antibody directed against the Modulo protein was chosen, rather than AJ1, because Modulo exhibits a differential localization within the nucleolus as a function of the state of replication of the nucleus.