Comparative physiology of Malpighian tubules: form and function

Abstract

Malpighian tubules (MTs) are the main osmoregulatory and excretory organs of insects and are considered analogous to the nephridia or kidneys, the corresponding organs of annelids and the vertebrates. MTs are responsible for the production of an isosmotic filtrate from hemolymph, the primary urine, which carries excretory products of metabolism and toxic compounds into the hindgut. The MTs of Drosophila (Diptera), the more representative studied insect, develop from the hindgut primordium and visceral mesoderm. Once formed, tubules in Diptera can grow in size to answer the increasing demands on osmotic and ionic regulation and renal clearance. However, there are up to 30 million species of insects occupying several ecological niches; therefore we can conclude that our models of transport and control of MTs cannot be generalistic. In this synthetic review, morphological and ultrastructural figures from hymenoptera, such as bees and ants, have been provided to illustrate the MTs from other insect groups. These organs have been widely used in ecotoxicological studies, as they quickly respond to changes in the insect's environment, and the tubules induce detoxification genes. The large number of scientific manuscripts around the world indicates that the MTs can be used for evaluation of biomarkers, detoxification, innate immunity, and as models for human renal diseases. Other studies have suggested that stem cells and progenitor cells may be involved in the repair and regeneration of injured renal tissue. Considering the different habitats of all organisms that have MTs, we can expect that the new techniques available for sequencing DNA and mRNA and the development of the omic-sciences, with the imminent sequencing of multiple insect genomes, will provide new data and further elucidate the different mechanisms by which MTs perform their functions.