Affiliation:
1. Göttingen Graduate School for Neurosciences, Biophysics, and Molecular Biosciences, Göttingen 37077, Germany
2. Department of Evolutionary Developmental Genetics, University of Göttingen, Johann-Friedrich-Blumenbach Institute, Göttingen Center for Molecular Biosciences, Göttingen 37077, Germany
Abstract
Animals from all major clades have evolved a segmented trunk, reflected in the human spine or the insect segments. These units emerge during embryogenesis from a posterior segment addition zone (SAZ), where repetitive gene activity is regulated by a mechanism described by the clock and wavefront/speed gradient model. In the red flour beetle
Tribolium castaneum
, RNA interference (RNAi) has been used to continuously knock down the function of primary pair-rule genes (pPRGs), caudal or Wnt pathway components, which has led to the complete breakdown of segmentation. However, it has remained untested, if this breakdown was reversible by bringing the missing gene function back to the system. To fill this gap, we established a transgenic system in
T. castaneum
, which allows blocking an ongoing RNAi effect with temporal control by expressing a viral inhibitor of RNAi via heat shock. We show that the
T. castaneum
segmentation machinery was able to reestablish after RNAi targeting the pPRGs
Tc-eve, Tc-odd,
and
Tc-runt
was blocked. However, we observed no rescue after blocking RNAi targeting Wnt pathway components. We conclude that the insect segmentation system contains both robust feedback loops that can reestablish and labile feedback loops that break down irreversibly. This combination may reconcile conflicting needs of the system: Labile systems controlling initiation and maintenance of the SAZ ensure that only one SAZ is formed. Robust feedback loops confer developmental robustness toward external disturbances.
Funder
Deutsche Forschungsgemeinschaft
Publisher
Proceedings of the National Academy of Sciences