Antagonistic role of the BTB-zinc finger transcription factors Chinmo and Broad-Complex in the juvenile/pupal transition and in growth control

During development, the growing organism transits through a series of temporally regulated morphological stages to generate the adult form. In humans, for example, development progresses from childhood through to puberty and then to adulthood, when sexual maturity is attained. Similarly, in holometabolous insects, immature juveniles transit to the adult form through an intermediate pupal stage when larval tissues are eliminated and the imaginal progenitor cells form the adult structures. The identity of the larval, pupal and adult stages depends on the sequential expression of the transcription factorschinmo, Br-CandE93. However, how these transcription factors determine temporal identity in developing tissues is poorly understood. Here we report on the role of the larval specifierchinmoin larval and adult progenitor cells during fly development. Interestingly,chinmopromotes growth in larval and imaginal tissues in a Br-C-independent and -dependent manner, respectively. In addition, we found that the absence ofchinmoduring metamorphosis is critical for proper adult differentiation. Importantly, we also provide evidence that, in contrast to the well-known role ofchinmoas a pro-oncogene, Br-C and E93 act as tumour suppressors. Finally, we reveal that the function ofchinmoas a juvenile specifier is conserved in hemimetabolous insects as its homolog has a similar role inBlatella germanica. Taken together, our results suggest that the sequential expression of the transcription factors Chinmo, Br-C and E93 during larva, pupa an adult respectively, coordinate the formation of the different organs that constitute the adut organism.