Metamorphosis of the Drosophila visceral musculature and its role in intestinal morphogenesis and stem cell formation

Abstract

The visceral musculature of the Drosophila intestine plays important roles in digestion as well as development. Detailed studies investigating the embryonic development of the visceral muscle exist; comparatively little is known about postembryonic development and metamorphosis of this tissue. In this study we have combined the use of specific markers with electron microscopy to follow the formation of the adult visceral musculature and its involvement in gut development during metamorphosis. Unlike the adult somatic musculature, which is derived from a pool of undifferentiated myoblasts, the visceral musculature of the adult is a direct descendant of the larval fibers, as shown by activating a lineage tracing construct in the larval muscle and obtaining labeled visceral fibers in the adult. However, visceral muscles undergo a phase of remodeling that coincides with the metamorphosis of the intestinal epithelium. During the first day following puparium formation, both circular and longitudinal syncytial fibers dedifferentiate, losing their myofibrils and extracellular matrix, and dissociating into mononuclear cells (“secondary myoblasts”). Towards the end of the second day, this process is reversed, and between 48 and 72h after puparium formation, a structurally fully differentiated adult muscle layer has formed. We could not obtain evidence that cells apart from the dedifferentiated larval visceral muscle contributed to the adult muscle, nor does it appear that the number of adult fibers (or nuclei per fiber) is increased over that of the larva by proliferation. In contrast to the musculature, the intestinal epithelium is completely renewed during metamorphosis. The adult midgut epithelium rapidly expands over the larval layer during the first few hours after puparium formation; in case of the hindgut, replacement takes longer, and proceeds by the gradual caudad extension of a proliferating growth zone, the hindgut proliferation zone (HPZ). The subsequent elongation of the hindgut and midgut, as well as the establishment of a population of intestinal stem cells active in the adult midgut and hindgut, requires the presence of the visceral muscle layer, based on the finding that ablation of this layer causes a severe disruption of both processes.

Developmentally Arrested Precursors of Pontine Neurons Establish an Embryonic Blueprint of the Drosophila Central Complex

“…No late pupa or adult flies survived under these circumstances, whereas non-temperature shifted controls were completely viable. This finding, in conjunction with previous results where the same upstream activating sequence (UAS)hid;rpr construct was effective in completely ablating muscle cells [28], supported the conclusion that our experimental (H-L) At 96 hr after hatching (late third instar), secondary DM1-DM4 axons have increased in number and form a system of crossing bundles, the posterior plexus of the fan-shaped body (FBppl in H, J, and K). Both R45F08-Gal4-positive fan-shaped body pioneers and secondary axons display tufts of filopodia, which appear as DN-cadherin-positive domains (fan-shaped body primordium, prEBp, and prEBa in I-L).…”

“…This bundle stands out from surrounding tracts by its higher electron density, being composed almost entirely of thin SU axons ( Figure 4D); furthermore, two paired glial cells ensheath the bundle on all sides (Figures 4D, 4G, and 4H). In late larvae, the pointed insertion R45F08-Gal4 is expressed in small subpopulations of neurons of DM lineages whose axons form a glia-covered commissural structure that will enlarge into the fan-shaped body and was therefore called fan-shaped body primordium ( Figure 4F) [28]. In first instar larvae, R45F08-Gal4 highlights four paired clusters of neurons in the dorso-medial brain whose axons form a thin tract that, in regard to size, central location within the brain commissure, and glial enclosure, corresponds to the structure identified electron microscopically ( Figure 4E).…”

Physiology, Development, and Disease Modeling in the Drosophila Excretory System

“…Currently, it is unclear whether this dual marker expression reflects the trans-differentiation of some hindgut cells into midgut cells, or whether cells originally expressing only hindgut markers transiently adopt a hybrid midgut/ hindgut gene expression pattern (Takashima et al 2013;Sawyer et al 2017). As the new adult pylorus and ileum emerge from anterior proliferation in the pylorus, macrophages appear to engulf the dying larval ileum (Aghajanian et al 2016). During this whole-scale remodeling of the hindgut epithelium, the overlying visceral musculature remains intact, leaving a sleeve-like scaffold within which the newly forming adult hindgut epithelium develops.…”

“…During this whole-scale remodeling of the hindgut epithelium, the overlying visceral musculature remains intact, leaving a sleeve-like scaffold within which the newly forming adult hindgut epithelium develops. Ablation of the visceral muscle disrupts the removal of the larval hindgut and construction of the adult hindgut, underscoring important muscle-epithelium cross-talk during this whole-scale organ remodeling event (Aghajanian et al 2016).…”

Remodeling of peripheral nerve ensheathment during the larval‐to‐adult transition in Drosophila

“…Interestingly, in the wax moth (both during larval and pupal stages), as well as the desert locust (Schistocerca gregaria), the cells of the perineurium seem to be responsible for the formation of the neural lamella and produce collagen or collagen-like fibrils for the NL (Ashhurst, 1965;Osi nska, 1981). Interestingly, a similar process of breakdown and rebuilding of the extracellular matrix is observed during metamorphosis of visceral musculature in Drosophila (Aghajanian et al, 2016). Here, the ECM has mostly disappeared by 24 h APF, re-building of the matrix begins around 48 h APF, and by 72 h APF, the ECM is seen as a dense membrane surrounding the muscle fibers.…”