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Biomedical subjects

V B Wigglesworth

Publications and source records attributed to V B Wigglesworth.

At least 19 recordsLinked to original sources
PubMed1985

Sclerotin and lipid in the waterproofing of the insect cuticle.

In all the cuticles studied waterproofing is effected by extracuticular material, a mixture of sclerotin precursors and lipids, exuded from the tubular filaments of the pore canals. In Rhodnius larval abdomen it is a layer of thickness similar to the outer epicuticle, believed to be composed of 'sclerotin' and wax, in Schistocerca larval sternal cuticle and in Carausius sternal cuticle it is similar. In Tenebrio adult sternal cuticle of the abdomen, in both the extracuticular exudation and the contents of the distal endings of the tubular filaments, the wax component is obscured by hard 'sclerotin'. In Manduca larva a very thin layer of 'sclerotin' and wax is covered by an irregular wax layer, average 0.75 micron, twice the thickness of the inner epicuticle. In Periplaneta and Blattella the abdominal cuticle is covered by a soft waxy layer, often about 1 micron thick, which is mixed with argentaffin material. Below this is a very thin waterproof layer of wax and 'sclerotin' continuous with the contents of the tubular filaments, which is readily removed by adsorptive dusts. In Apis adult abdominal terga free wax plus sclerotin precursors form a thin layer which is known to be removed by adsorptive dusts. In Calliphora larva there is a very thin layer of the usual mixed wax and sclerotin and below this a thick (0.5 micron) layer, lipid staining and strongly osmiophil, likewise extracuticular and exuded from the epicuticular channels. This material (which is often called 'outer epicuticle') has the same staining and resistance properties as the true outer epicuticle on which it rests. In the abdomen of Calliphora adult the waterproofing wax-sclerotin mixture forms a thin layer over the entire cuticle including the surface of the microtrichia. There is also a thin detachable layer of free wax on the surface.

Abdomen↗
PubMed1985

The transfer of lipid in insects from the epidermal cells to the cuticle.

The structure of the pore canals and the tubular filaments they contain are described in a series of insects and types of cuticle. In all these cuticles the tubular filaments arise from the plasma membrane of the epidermal cells and they contain argentaffin material, regarded as sclerotin precursors, and lipid-staining material, regarded as wax precursors. These materials are transferred to the inner epicuticle and are exuded over the surface of the outer epicuticle to form the waterproofing layer as described in the preceding paper. They are also transported to those parts of the endocuticle destined to form hard exocuticle. There are no terminations of tubular filaments in the soft cuticle of Manduca larva, in the soft expanding cuticle of Rhodnius, and in the non-sclerotized post-ecdysial endocuticle of Tenebrio. Apis. etc. In the puparium of Calliphora lipid appears to be added by the epidermal cells directly and not by way of tubular filaments. It is confirmed that lipid is a component of sclerotized cuticle.

Animals↗
PubMed1982

The supply of oxygen to the flight muscles of insects: a theory of tracheole physiology.

In the flight muscles of insects, virtually every mitochondrion is in contact with or is encircled by terminal tracheoles which reach them by following the channels formed by the invaginated plasma membrane of the muscle fibres, the T-system tubules. In musca, Calliphora and Drosophila (Diptera), Apis (Hymenoptera) and Tenebrio (Coleoptera) the terminal tracheoles are smooth-surfaced tubes with a lumen of about 50 nm. In Pieris (Lepidoptera) the terminal tracheoles occupy the regular transverse tubular system which runs between the mitochondria and across the fibrils on either side of the H zone. They are smooth tubules of 80-200 nm diameter. Preliminary observations suggest the same arrangement in Ischnura (Odonata). In Rhodnius and other Hemiptera the transverse T-tubule system forms large cavities among the mitochondria: these cavities in Rhodnius are occupied by smooth-walled tracheole endings. In the nature adult of Schistocerca (Orthoptera) T-tubules of varying size are utilized by terminal tracheoles (diameter 50-100 nm). The terminal tracheoles of the flight muscles are highly permeable to myrcene and kerosene. They commonly fill with liquid during rest and this liquid is resorbed during activity. It is suggested that these adaptations increase the efficiency of respiration in the flight muscles by ensuring that, when it is most needed, gaseous oxygen extends to the surface of the mitochondria, from which it is separated by a very permeable barrier.

Animals↗
PubMed1981

The distribution of lipid in the cell structure: an improved method for the electron microscope.

An improved partition method for visualizing lipid consists in fixing tissues in paraformaldehyde-glutaraldehyde followed by osmium tetroxide. Three progressive grades of lipid staining are then obtained: (i) by renewed osmium tetroxide alone, (ii) by partition in myrcene or farnesol solutions followed by renewed osmium, (iii) by saturated thymol in sucrose followed by partition and renewed osmium. No additional metallic stains are used. The thymol treatment in (iii) renders 'masked' lipid accessible to partition--the effect being regulated as required by time and temperature. Thymol used before the first osmium facilitates lipid extraction which provides a complementary test for lipid. The possibilities of the method have been demonstrated on sections of familiar tissues of insect (mainly Rhodnius, Hemiptera) and mammal (mouse). By and large the results support what is known already about the distribution of lipid in cells, but observations on lipid in muscle fibres, in the nucleolus and chromatin, in the cells of the adrenal cortex, in the lung and intestine suggest that the method might prove a source of new information.

Acyclic Monoterpenes↗
PubMed1979

Secretory activities of plasmatocytes and oenocytoids during the moulting cycle in an insect (Rhodnius).

Plasmatocytes in Rhodnius appear to be the chief source of the basement membrane (basal lamina) of the abdominal epidermis. The membrane increases three-fold in thickness while the cells are applied to its surface, from 4 to 9 days after feeding. At this time irregular deposits of membrane substance appear, applied to the membrane in the vicinity of plasmatocytes. Many small vesicles perhaps undergoing exocytosis are seen at the surface of the plasmatocytes in contact with the basement membrane (basal limina). The large granular inclusions of the plasmatocytes are dispersed and their contents appear to provide the substance of the basement membrane, which has the same staining properties as these inclusions.

Animals↗
PubMed1977

Structural changes in the epidermal cells of Rhodnius during tracheole capture.

Epidermal cells deprived of their oxygen supply by tracheal section give off cytoplasmic processes which become attached to air-filled tracheoles in neighbouring areas and draw these into the oxygen-deficient zone. Many of these cytoplasmic strands exceed 100 micrometer in length but may be no more than 50 nm in diameter; they contain mitochondria, ribosomes, microtubules and microfilaments. In basis structure they resemble the tendon cells; and also the tapering conical epidermal cells along the intersegmental borders of the abdomen, the terminal strands of which are inserted into the basement memebrane behind and in front of the segmental boundaries. The cytoplasmic walls of those tracheoles most exposed to tension during the process of tracheole capture become thickened and packed with microtubules. In all these structures the microtubules are believed to be concerned in resistance to tension. Contraction is presumably effected by microfilaments, but no new evidence is given. The possible role of the epidermal strands in the transport of energy-rich metabolites is discussed.

Animals↗
PubMed1975

Lipid staining for the electron microscope: a new method.

Tissues fixed in osmium tetroxide or in combined osmium and glutaraldehyde (Hinde), embedded in Spurr's medium, cut at 0-5-I mum and mounted in Farrants' gum medium containing ethyl gallate, show good staining of lipid-contaning structures (droplets of triglyceride, membranes, mitochondria, etc.) in the light microscope. Such preparations show moderate contrast in the electron microscope without further staining. But a specific increase in contrast in lipid-rich structures is obtained by partition of the tissues, before embedding, in 70% ethanol saturated with the monoterpene hydrocarbon myrcene, with or without the addition of 0-I % ethyl gallate, followed by osmium tetroxide. This method will visualize both saturated and unsaturated lipids, including waxes.

Animals↗
PubMed1975

Distribution of lipid in the lamellate endocuticle of Rhodnius prolixus (Hemiptera).

The lamellate appearance of the cuticle in the abdomen of the Rhodnius larva conforms to the conception of Bouligand in being an optical artifact which results from the spiral arrangement of successive layers of oriented fibrils. But superimposed on this structure is an actual lamination of bound lipid with the same spacing. The relation of the lipid layers to the optical lamination changes with the aspect from which the system is viewed. There must therefore be a cyclical secretion of lipid by the epidermal cells. Since the period of this cycle agrees with the cycle of rotation of the fibrous layers, which is supposedly inherent in the chemistry of the system, it is possible that it is the lipid which controls or initiates this helicoidal 'cholesteric crystallization'. There is evidence of a cyclical change in the secretion of lipid by the microvilli; it is suggested that there may be alternating cycles of eccrine and apocrine secretion, and that the lipid laminae represent the apocrine phases. The pore canals in Rhodnius are roughly cylindrical in cross-section, with lipid-impregnated walls. The contents of the lumen become slightly more electron opaque before the cuticle is stretched by feeding. There is probably some enzymic dissolution of the cuticle which precedes stretching; and this may concern particularly the lipid fraction. After the great distension and expansion of the cuticle which occur at feeding, lipid laminae can no longer be demonstrated in the old cuticle.

Animals↗
PubMed1975

Incorporation of lipid into the epicuticle of Rhodnius (Hemiptera).

The incorporation of lipid into both the outer and inner epicuticle during deposition is described. Waterproofing of the epicuticle by secretion of the wax layer, and sclerotization with or without melanization, are controlled from a distance by the epidermal cells by way of the pore canals. The pore canals gradually narrow as they approach the epicuticle. On reaching the inner epicuticle the canal ends in a conical projection from the apex of which a permeable lipophilic channel about 20-25 nm in diameter runs vertically to the apex of which a permeable lipophilic channel about 20-25 nm in diameter runs vertically to the surface. Shortly before ecdysis, silver-binding material (perhaps protein rich in tyrosine, or other precursors concerned in sclerotization) spreads radially from a point in the cuticular channels just below the outer epicuticle, and gradually impregnates the outer two thirds or more of the inner epicuticle. The precise pattern varies in different cuticular structures. Argentaffin materials (polyphenols) first appear in these same sites at the time of ecdysis and increase rapidly during the next 24 h. Lipid appears in the lumen of the distal parts of the pore canals (with a patchy distribution) shortly before ecdysis. When digestion and absorption of the old endocuticle are almost complete, minute lipid droplets appear on the surface of the epicuticle, apparently exuded from the epicuticular channels, and spread to make a uniform layer. When first formed this layer strains readily with Sudan B, but the lipid becomes incorporated in a delicate non-lipid silver-binding membrane (also exuded from the epicuticular channels) and hardens just before ecdysis, to form the so-called 'wax layer' which then no longer stains with Sudan B. Within half an hour after ecdysis the alcian blue-staining cement layer is poured out by the dermal glands, and forms a continuous but somewhat irregular covering over the 'wax layer'. Changes in the epicticle that accompany the repair of abrasions are described.

Animals↗