Alveolar proteins stabilize cortical microtubules in Toxoplasma gondii

Single-celled protists use elaborate cytoskeletal structures, including arrays of microtubules at the cell periphery, to maintain polarity and rigidity. The obligate intracellular parasite Toxoplasma gondii has unusually stable cortical microtubules beneath the alveoli, a network of flattened membrane vesicles that subtends the plasmalemma. However, anchoring of microtubules along alveolar membranes is not understood. Here, we show that GAPM1a, an integral membrane protein of the alveoli, plays a role in maintaining microtubule stability. Degradation of GAPM1a causes cortical microtubule disorganisation and subsequent depo-lymerisation. These changes in the cytoskeleton lead to parasites becoming shorter and rounder, which is accompanied by a decrease in cellular volume. Extended GAPM1a depletion leads to severe defects in division, reminiscent of the effect of disrupting other alveolar proteins. We suggest that GAPM proteins link the cortical microtubules to the alveoli and are required to maintain the shape and rigidity of apicomplexan zoites

Morphology and larval development of the parasitoid fly Exorista larvarum (L.)

This study reveals the morphology of immature E. larvarum and the changes during its development and offers detailed investigations on the larval body structures from the histological point of view

LARVAL MORPHOLOGY AND ANATOMY OF THE PARASITOID EXORISTA LARVARUM (DIPTERA: TACHINIDAE), WITH AN EMPHASIS ON CEPHALOPHARYNGEAL SKELETON AND DIGESTIVE TRACT

The endogenous development of the tachinid gregarious larval parasitoid Exorista larvarum (L.) (Diptera: Tachinidae) has been analyzed in the last larval instar of a factitious host, the wax moth Galleria mellonella (L.) (Lepidoptera: Pyralidae), using histological techniques and scanning electron microscopy. This study has focused on the parasitoid internal body structures and their changes during the larval development. The first and second instar are enveloped by a host-derived hemocyte capsule attached to the respiratory funnel via a prominent anal hook located between 2 anal lobes. The third instar abandons the respiratory funnel and migrates free in the body cavity of the already dead host. Emphasis is given to the prominent cephalopharyngeal skeleton, highlighting the morphological aspects of its sclerotized as well as non-sclerotized components. In addition to the cephalopharyngeal skeleton, the anterior third of the larval parasitoid body is occupied by large salivary glands, massive proventriculus, and cerebral ganglia. The extensive digestive tract, which occupies the major part of the body, is differentiated into well-marked individual parts. The abdomen is predominantly filled with the extremely long mesenteron that increases in size during the larval development. The whole body is covered by an apparently thin integument, with strong spines that are especially numerous in the anterior and posterior body parts

Development of the larval parasitoid fly, Exorista larvarum (Diptera: Tachinidae) with emphasis in its movements and attachment strategy to the host tissue

Exorista larvarum (L.) is a polyphagous gregarious larval endoparasitoid of Lepidoptera. Female flies deposit macrotype eggs on the host surface. The newly-hatched larva penetrates the host integument, induces the formation of a primary integumental respiratory funnel and develops through three larval instars. Pupation generally occurs outside the host larval remains. The morphology of larval E. larvarum was studied in its factitious host Galleria mellonella (L.) (Lepidoptera: Pyralidae). Last instar host larvae were exposed for parasitization to female flies and removed when the 3 - 5 eggs had been laid on their body. Parasitized larvae were dissected and fixed every day of the parasitoid development, which lasts 3 - 4 days from egg hatching to pupal stage at 26°C. Specimens were embedded in Histoplast II and sections 5 - 7 µm thick were stained with hematoxylin - eosin and Masson΄s trichrome stain. To obtain sections of better quality, the cryosection and rapid microscopic analysis were also used. Frozen sections were stained with azan or hematoxylin - eosin. Here, we focus on the integument and related structures participating in the movements and attachment process of E. larvarum larva to the host tissue. The tachinid larva penetrates the host using the robust cephalopharyngeal skeleton that undergoes changes during larval development. Using mouthhooks, it feeds on host hemolymph and subsequently on fat body and other host tissues. During larval development the digestive tract gradually becomes more extensive and denotes a great increase in the third instar, which abandons the funnel and migrates in the host body cavity. The tracheal system with prominent respiratory plates is well developed in all larval instars. The larvae are equipped with a thick anal hook and numerous cuticular spines supporting the larva in their attachment to the respiratory funnel. The external morphology of E. larvarum larvae of all instars was studied by electron microscopy. The behaviour of E. larvarum larvae in the host tissues and the escape of the advanced-third instar larvae from the host carcass were documented in vivo using the light microscope

Penetration and encapsulation of the larval endoparasitoid Exorista larvarum (Diptera: Tachinidae) in the factitious host Galleria mellonella (Lepidoptera: Pyralidae)

The tachinid fly Exorista larvarum (L.) (Diptera: Tachinidae) is a polyphagous larval endoparasitoid that deposits its eggs on the host exoskeleton of lepidopteran and tenthredinid larvae. The attachment of larval E. larvarum and the formation of the respiratory funnel were studied during infestation in the last larval instar of the wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae). The tachinid larvae burrow through the host integument after hatching, using their robust cephalopharyngeal skeleton, leaving a dark spot at the point of their penetration as a result of host cuticle melanization. Endoparasitoid penetration induces the host cellular defence, resulting in the formation of a haemocyte capsule consisting of multi-cellular sheaths. This enveloping capsule later undergoes melanization, which is mostly obvious towards the posterior part of the endoparasitoid. The endoparasitoid uses the host encapsulation response to build a respiratory funnel from the modified host integument, leading to the host surface. The encapsulated larva remains attached to the respiratory funnel via an anal hook and cuticular spines until fully developed. Additional immunohistochemical analyses were used to study host\u2013parasitoid interactions. Indirect immunofluorescence showed no labelling of potential tachinid antigens and confirmed no effect on the surrounding host tissues. A simulated parasitization with coated polybead microspheres revealed the mortal impact of tachinid antigens to the host. Hosts injected with antigen-coated polybeads died as a consequence of an acute and extensive immunological response to the tachinid antigens and not due to the trauma caused by foreign objects inside their body.