Post-embryonic development of the Malpighian tubules in Apis mellifera (Hymenoptera) workers: morphology, remodeling, apoptosis, and cell proliferation

Abstract

The honeybee Apis mellifera has ecological and economic importance; however, it experiences a population decline, perhaps due to exposure to toxic compounds, which are excreted by Malpighian tubules. During metamorphosis of A. mellifera, the Malpighian tubules degenerate and are formed de novo. The objective of this work was to verify the cellular events of the Malpighian tubule renewal in the metamorphosis, which are the gradual steps of cell remodeling, determining different cell types and their roles in the excretory activity in A. mellifera. Immunofluorescence and ultrastructural analyses showed that the cells of the larval Malpighian tubules degenerate by apoptosis and autophagy, and the new Malpighian tubules are formed by cell proliferation. The ultrastructure of the cells in the Malpighian tubules suggest that cellular remodeling only occurs from dark-brown-eyed pupae, indicating the onset of excretion activity in pupal Malpighian tubules. In adult forager workers, two cell types occur in the Malpighian tubules, one with ultrastructural features (abundance of mitochondria, vacuoles, microvilli, and narrow basal labyrinth) for primary urine production and another cell type with dilated basal labyrinth, long microvilli, and absence of spherocrystals, which suggest a role in primary urine re-absorpotion. This study suggests that during the metamorphosis, Malpighian tubules are non-functional until the light-brown-eyed pupae, indicating that A. mellifera may be more vulnerable to toxic compounds at early pupal stages. In addition, cell ultrastructure suggests that the Malpighian tubules may be functional from dark-brown-eyed pupae and acquire greater complexity in the forager worker bee.

Cell death during complete metamorphosis

“…In the honeybee, Apis mellifera, the intervention of PCD has been described in many developmental processes [81], not strictly related to metamorphosis. During the larvapupa transition, a concomitant activation of autophagy and apoptosis is necessary for the removal of the larval midgut [82], the hindgut [83], salivary glands [84,85] and Malpighian tubules [86]. In particular, in the salivary glands, autophagy and apoptosis act in a coordinated manner to reduce the thickness of the larval epithelium by releasing cytoplasmic protrusions from the apical side of the cells.…”

Periviscerokinin (Cap2b; CAPA) receptor silencing in females of Rhipicephalus microplus reduces survival, weight and reproductive output

“…One potential role of the periviscerokinin (CAP 2b /PVKs) system in embryos of ticks could be control of myotropic activity, since muscle contraction was observed in embryos of the coleopteran insect Callosobruchus maculatus [ 72 ], but no peptides associated with the regulation of this process have been identified to date. Another known function of the CAP 2b /PVK system in insects is diuretic; however, Malpighian tubules are under a process of cell proliferation and differentiation during embryonic development, and these are not fully functional until the larval stage (see, for example, [ 73 , 74 ]); therefore, a function of the CAP 2b /PVK receptor in embryo Malpighian tubules is less likely.…”

Excretion in the mother’s body: modifications of the larval excretory system in the viviparous dermapteran, Arixenia esau

“…This notion is supported by remarkable similarity of the ultrastructure of the Arixenia larval Mt epithelial cells to the ultrastructural organization of such cells in many insects (e.g., Ryerse 1979 ; Hanrahan and Nicolson 1987 ; Arab and Caetano 2002 ; Goncalves et al 2014 ; Lipovsek et al 2017 ; Liu and Hua 2018 ). It should be mentioned here that in larvae of some holometabolous insects, e.g., Apis mellifera , differences in Mt organization may occur that are associated with substantial remodeling of the internal organs accompanying complete metamorphosis (for further details, see Goncalves et al 2018 ).…”