Malpighian tubule development in the red flour beetle (Tribolium castaneum)

• A detailed description of Tribolium embryonic Malpighian tubule (MpT) development is provided.
• Tribolium MpTs have shared and derived morphological, cellular and molecular features compared to Drosophila.
• Tribolium MpTs are shaped by oriented cell division.
• A description of cell diversity in developing and adult Tribolium tubules is provided.
• Use of cross-reacting antibodies and enhancer trap line to report expression of Tc-Cut, Tc-Tio, Tc-Spi, Tc -dpERK, Tc-phospho-Histone H3.

Malpighian tubules (MpTs) are the major organ for excretion and osmoregulation in most insects. MpT development is characterised for Drosophila melanogaster, but not other species. We therefore do not know the extent to which the MpT developmental programme is conserved across insects. To redress this we provide a comprehensive description of MpT development in the beetle Tribolium castaneum (Coleoptera), a species separated from Drosophila by >315 million years. We identify similarities with Drosophila MpT development including: 1) the onset of morphological development, beginning when tubules bud from the gut and proliferate to increase organ size. 2) the tubule is shaped by convergent-extension movements and oriented cell divisions. 3) differentiated tip cells activate EGF-signalling in distal MpT cells through the ligand Spitz. 4) MpTs contain two main cell types – principal and stellate cells, differing in morphology and gene expression. We also describe development of the beetle cryptonephridial system, an adaptation for water conservation, which represents a major modification of the MpT ground plan characterised by intimate association between MpTs and rectum. This work establishes a new model to compare MpT development across insects, and provides a framework to help understand how an evolutionary novelty – the cryptonephridial system – arose during organ evolution.