Giulio Lanzavecchia

Morphological modulations in helical muscles (Aschelminthes and Annelida).

Publisher Summary This chapter discusses the morphological modulations in helical muscles. Helical muscles may be considered a category of striated muscle, despite the fact that they have some of the physiological properties of smooth muscles. Although the helical fibers described in different animal species are similar in organization, certain categories may nevertheless be distinguished, each with its own arrangement of contractile material. In all instances, the contractile material appears to be located at the periphery of the fiber, and may occupy the whole or only part of the perimeter. Helical fibers have been described in only a few animal groups, mainly nematodes, annelids, and mollusks. The transition from typical smooth to helical fibers in mollusks may come about in several ways, and there are some fast fibers with marked transverse striation. Specialized fibers are associated with the alimentary tract or with reproductive systems, but their fine structure is practically unknown.

Structure and demolition of yolk in Rana esculenta L.

The early stages of demolition process of the yolk globule crystalline body in frog embryos have been studied with the electron microscope. This process consists of a progressive detachment of the protein structural units, following the hexagonal pattern of the lattice. The process is identical for numerous superimposed layers of hexagonal cells of the crystal. The mitochondrial crystals of yolk show a different structure from that of the yolk globules. They are presumably constituted by a hexagonal array of indefinitely long cylinders, of an electron-transparent material, encompassed by an electron-dense band. During embryological development they become thinner and thinner, while retaining their hexagonal form. The significance of these observations, in relation both to embryological development and yolk synthesis period are discussed.

Superelongation in helical muscles of leeches

SummaryThe fine structure of leech body wall muscles, has been analysed under great length variations. All the measurable parameters of the fibre (distance between thick filaments, sarcomere and A band width, percentage of actin crowns around myosin filaments, fibre radius) at different elongations were tested with equations describing the geometrical model of helical fibres.Anaesthetized and nonanaesthetized worms behave in different ways and can be utilized to verify the ‘changing partner hypothesis’. The fit between theoretical and experimental data suggests that a double change of partner actually takes place in extremely stretched fibres.

Hirudo medicinalis: A new model for testing activators and inhibitors of angiogenesis

An increasing body of evidence indicates that in the leech Hirudo medicinalis the angiogenic process is finely regulated and coordinated by the botryoidal tissue. In this paper we provide evidence on the involvement of botryoidal tissue cells in angiogenesis induced in H. medicinalis by a variety of stimuli including surgical wounds or the administration of modulators of neovascularization. Interestingly, we show that either human activators of vascular cell growth, or anti-angiogenic peptides like angiostatin and endostatin, or the drug mitomycin, can induce a prompt biological response in H. medicinalis. We show as well that angiogenesis in this invertebrate shares a surprising degree of similarity with neovascularization in vertebrates, both at the biochemical and cellular levels, because it involves similar growth factors/growth factor receptors, and relies on analogous cell–cell or cell–matrix interactions. For these reasons we suggest that H. medicinalis can be used as a reproducible model for testing activators or inhibitors of angiogenesis, and for investigating the biochemical, ultrastructural and cellular processes involved in new vessel formation.

The spermatozoon of peracarida. I. The spermatozoon of terrestrial isopods

Spermatozoa of isopods belonging to the suborder of Oniscoidea have been studied by means of electron microscopy, both in sections and in negatively stained whole mounts. The motionless sperm is composed of a complicated acrosomal complex, a filamentous nucleus with uncondensed chromatin, a long paracrystalline perforatorium, a couple of peculiar centrioles, and some mitochondria; the head articulates with a very long paracrystalline, banded rod (“tail”). The single sperms are grouped in spermatophores, delimited by a sheath of tightly packed tubules about 420 A in diameter.

Comparative electron microscopic studies of muscle and sperm cells inBranchiobdella pentodonta whitman andBythonomus lemani grube (Annelida clitellata)

SummaryTo determine the degree of systematic affinity between branchiobdellids and lumbriculids, the ultrastructures of muscle and sperm cells ofBranchiobdella pentodonta andBythonomus lemani were studied.The structure ofBranchiobdella sperms is similar to that of the oligochaete model in terms of nucleus and the middle piece and to that of the hirudinean model in the peculiarity of the flagellum and acrosomal complex. Muscle ofBranchiobdella are very similar to those of the hirudineans.Muscles and sperms ofBythonomus lemani are practically identical to those of the tubificid model and are closely related to the other known oligochaetes.

Three-dimensional reconstruction of the contractile system of the Nematomorpha muscle fiber.

The body-wall muscle fiber of Nematomorpha (flattened circomyarian with central cytoplasmic axis) is characterized by very long (about 120 μ m) bipolar, paramyosinic filaments with a periodic asymmetrical organization. They are arranged in longitudinal contractile fields and form paired systems of very elongated semihelices regularly staggered along the fiber axis, concave toward the periphery and alternatively enantiomorphic. A three-dimensional reconstruction of the contractile system was performed considering the morphology of the contractile fields, the position in these latter of the central reversal zones and tapered extremities of thick filaments, and the peculiar distribution in the direction of the filament polarity. The validity of the possible models was checked comparing the actual images visible under the electron microscope with those obtainable by means of a computer. The possible functional meaning of this contractile structure is briefly discussed.

Leech responses to tissue transplantation

The aim of the present work is to describe histologically, histochemically and immunocytochemically, the sequence of events that lead to first and second set rejection of allo- or xenograft in leeches. Graft responses of leeches are comparable and are described following specific steps: inflammatory phase, rejection phase and granulation tissue formation (including re-epithelialisation, angiogenesis and fibroplasia).The responses to first and second graft in first set graft rejection as well as to the first transplant in second set graft experiments are identical and in the time span of a week all grafts are destroyed and disappear. In the second set graft rejection experiments the responses against the second transplant are markedly accelerated. The second graft shows massive structural alterations and it is rapidly rejected, within 3-4 days.Our results permit to highlight that in leeches there is a specific responsiveness of immune system similar to those described in highly divergent phyla.

Leeches: Immune Response, Angiogenesis and Biomedical Applications

The innate immune response is the first line of defence strategies in invertebrates against attack of infectious agents. A detailed analysis of the immune mechanisms involved in annelids has been performed in oligochaets, but few data are available in polichaets and hirudineans. The aim of this review is to describe the responses of leeches to different kinds of stimuli (infections following non-self agent attacks, surgical lesions, grafts). Furthermore, the use of this invertebrate as a novel experimental model to be used to screen drugs and genes, which are responsible for positive and negative modulation of angiogenesis, is discussed.

Morphofunctional and phylogenetic relations in helical muscles

Abstract The distribution of obliquely (helical) and cross-striated muscles, and their physiological and mechanical properties, are analyzed throughout the zoological scale in relation to the presence and the functional requirements of different types of skeletal systems. It is suggested that helical fibres are an evolutionary answer to the appearing of the hydroskeleton, being able to develop high active tensions also in conditions of superelongation. The mechanism by which this unique property is realized depends on the possibility of a typical change in the relationships between thick and thin filaments of the same sarcomere.