Midgut pseudotumors and the maintenance of tissue homeostasis: Studies on aging and manipulated stick insects

Abstract

Stick insects (Carausius morosus) develop pseudotumors in aging adults. Pseudotumor formation starts at the M2 midgut region where an accumulation of stomatogastric nerve terminals is observed. Pseudotumors arise from dying columnar cells whose basal parts form an "amorphous substance" at the basement membrane whereas the apical parts, including the nucleus, are expelled into the gut lumen. The "amorphous substance" is ensheathed by hemocytes. These nodules, which do not melanize, characterize the phenotype of the pseudotumors. With age, cell death and pseudotumor infestation increases. It is shown that the maintenance of midgut tissue homoeostasis is disturbed and becomes more serious with growing pseudotumor incidence. The increased death rate of differentiated columnar cells is no longer compensated by the proliferation of regenerative cells, i.e., intestinal stem cells, in the midgut nidi. The appearance of "holes" in the intestinal wall is evidently a causative factor of premature death. Extirpation of the hypocerebral ganglion in young adults of the stick insect (before the onset of spontaneous pseudotumor formation) provokes the apoptosis of a large number of columnar cells within 24 h and the formation of pseudotumors that are histologically identical with spontaneous ones. We conclude that the stomatogastric nervous system plays a decisive role in the regulatory mechanism maintaining midgut tissue homeostasis. The possibility of experimentally manipulating the regulatory system provides a valuable tool for the exploration of extrinsic factors involved into the feedback circuitry of tissue homeostasis. The fact that comparable pseudotumors were observed in a number of orthopteromorphan species, where they could also be induced by the interruption of the stomatogastric nervous system, indicates that its role in tissue homoeostasis may be widespread in insects and possibly represent a general principle.

Vital staining of the stick insect digestive system identifies appendices of the midgut as novel system of excretion

“…The phasmid midgut is divided into two sections based on morphology: the anterior third to half of the midgut is heavily pleated and folded, whereas the posterior third of the midgut is studded with a variable number of ampules that terminate with long, thin filaments that run toward the posterior of the insect, referred to as the “appendices of the midgut” and not found in any of the proposed Phasmid sister orders (Lacombe, ; Nation, ; Klass et al ). Although most authors describe the midgut as having two parts (Cameron, ; Chopard, ; Clark, ), undifferentiated regions between the pleated and appendices‐containing sections and between the latter and the hindgut are occasionally counted as distinct midgut sections for four sections total (Holtmann and Dorn, ). At the junction between the midgut and hindgut, as in most other insects, are over one hundred Malpighian tubules, which are the primary organs of excretion.…”

DEAD-Box RNA Helicase DDX47 Maintains Midgut Homeostasis in Locusta migratoria

“…In insects, this complex coordinated activity is involved in the regulation of programmed cell death, cell proliferation, and differentiation [ 1 , 2 , 3 ]. It is an essential dynamic process for the survival of insects, which can be affected by both internal and external factors, such as hormones and growth regulators, temperature and other environmental factors [ 1 , 2 , 12 , 13 , 14 , 15 ].…”