Striated visceral muscle of Drosophila melanogaster

Abstract

Striated visceral muscle cells are scattered singly or in small groups at the base of the intestinal cells of the mid-gut of Drosophila melanogaster larvae. Fibers less than 1 , U in diameter, designated as small, contain a single myofibril, few, if any, dyads and few mitochondria. Fibers of somewhat larger diameter contain dyads and more mitochondria. Both types of fiber have a perforate Z band which appears as discontinuous bodies in longitudinal sections and as a perforate sheet of dense rims and clear perforations in transverse sections. The Z rims contain filaments, 30 to 50 A, oriented in the transverse direction. The number and arrangement of myofilaments and the ultrastructure of the Z band are consistent with the function of these muscles.Dipteran visceral fibers that perform slow contractions resembling those of the functionally comparable smooth muscle of vertebrate intestine are striated (Schaeffer et al., '67). The general organization of these striated visceral fibers, the cellular membranes and organelles, and the myofilament array are all characteristic of other slowly contracting invertebrate striated muscles. In addition, these visceral fibers contain separate clumps of Z material or Z bodies. This incomplete Z band is present in striated muscles which can supercontract to less than 50% of rest length (Leyton and Ullrick, '70; Osborne, '67).Although the ultrastructure of visceral muscles in several other insects has been reported (Kawaguti, '67; Smith et al., '66; Schaeffer et al., '67; Smith, '68), it seemed desirable to analyze the myofilament arrangement and fine structure of Z bands in greater detail and to explore additionally the assumption that these muscles can undergo supercontraction. The larval midgut from Drosophiln melunogaster was used in the investigation. MATERIALS AND METHODSIntact third-instar (85 to 90 hours) of Drosophila melanognster were placed in 4% paraformaldehyded% glutaraldehyde fixative, (Karnovsky, '65) for one hour and then diced and fixed for an additional 90 J. MORPH., 134: 315-334.minutes. The tissue was rinsed in buffer for two hours and then post-fixed in 1% osmium tetroxide. After rapid dehydration in increasing concentrations of ethanol, the tissue was embedded in Epon (Luft, '61)? and thin sections were cut with a diamond knife on a Porter Blum MT-2 ultramicrotome. The sections were stained with a saturated solution of uranyl acetate in 50% ethanol, post-stained with lead citrate (Reynolds, '63) and examined in a Siemen's Elmiskop I A. RESULTSThe mid-gut epithelium consisted primarily of columnar absorptive cells with apical microvilli and numerous infoldings of the basal cell membrane ( figs. 2-3). Small undifferentiated cells without basal infoldings and containing many free ribosomes constituted adjacent replacements ( fig. 2). Cells constituting visceral muscle were arranged in circular and longitudinal arrays ( fig. 1 ). Striated muscle cells were scattered singly or in small groups in the extracellular matrix at the base of the intestinal cell...

Ultrastructure and morphology of midgut visceral muscle in early pupal Aedes aegypti mosquitoes

“…aegypti and An. gambiae (Park and Shahabuddin, 2000) and fruit fly Drosophila melanogaster (Goldstein and Burdette, 1971), as well as the larval M. sexta (Copenhaver et al, 1996) and Ae. aegypti (Bernick et al, 2007).…”

Organization, ultrastructure, and development of midgut visceral muscle in larval Aedes aegypti

“…Goldstein et al (1971) reported that, in the visceral muscle of larval D. melanogaster, H bands (containing myosin only) were ambiguous in longitudinal section. A bands were highly variable, as the thinner actin filaments were scattered in a highly random manner throughout the fiber.…”

“…The scarcity of these structures is extreme even by comparison with the adult mosquito Anopheles quadramaculatus (Schaeffer et al, 1967) or larval fruit fly Drosophila melanogaster (Goldstein et al, 1971). However, reduced sarcoplasmic reticulum cisternae are common to many insect visceral and slow-twitch skeletal muscles (Klowden 2002).…”

“…Based on epithelial cell morphology and topography, three distinct regionsthe anterior midgut, posterior midgut, and an intermediate transition zone-have been described (Clark et al, 2005). The muscularis is composed of bands of longitudinal and circular muscle (Park et al, 2000,Goldstein et al, 1971Copenhaver et al, 1996) which form a mesh-like grid. This contrasts with the visceral smooth muscle characteristic of vertebrates, where both circular and longitudinal muscle is found in discrete sheets or layers separated by the nerves of the enteric plexus.…”

Temporal ChIP-on-chip reveals Biniou as a universal regulator of the visceral muscle transcriptional network

“…Drosophila embryos have four types of VM that all contribute to the gut musculature (for review, see Lee et al 2005). Despite their different embryological origins, all VM in flies and humans display slow supercontractions, distinguishing them from skeletal (somatic) and cardiac muscle (Goldstein and Burdette 1971;Bitar 2003).…”