Endothelial and hematopoietic cells appear synchronously on the extra-embryonic membranes of amniotes in structures known as blood islands. This observation has led to the suggestion that these two ventral lineages share a common progenitor. Recently, we have shown in the zebrafish, Danio rerio, that a single cell in the ventral marginal zone of the early blastula can give rise to both endothelial and blood cells as well as to other mesodermal cells (Stainier, D. Y. R., Lee, R. K. and Fishman, M. C. (1993). Development 119, 31–40; Lee, R. K. K., Stainier, D. Y. R., Weinstein, B. M. and Fishman, M. C. (1994). Development 120, 3361–3366). Here we describe a zebrafish mutation, cloche, that affects both the endothelial and hematopoietic lineages at a very early stage. The endocardium, the endothelial lining of the heart, is missing in mutant embryos. This deletion is selective as evidenced by the presence of other endothelial cells, for example those lining the main vessels of the trunk. Early cardiac morphogenesis proceeds normally even in the absence of the endocardium. The myocardial cells form a tube that is demarcated into chambers, beats rhythmically, but exhibits a reduced contractility. This functional deficit is likely due to the absence of the endocardial cells, although it may be a direct effect of the mutation on the myocardial cells. Cell transplantation studies reveal that the endothelial defect, i.e. the endocardial deletion, is a cell-autonomous lesion, consistent with the possibility that cloche is part of a signal transduction pathway. In addition, the number of blood cells is greatly reduced in cloche mutants and the hematopoietic tissues show no expression of GATA-1 or GATA-2, two key hematopoietic transcription factors that are first expressed during early embryogenesis. These results show that cloche is involved in the genesis and early diversification of the endothelial and blood lineages, possibly by affecting a common progenitor cell population.

cloche, an early acting zebrafish gene, is required by both the endothelial and hematopoietic lineages

The vertebrate immune system is comprised of numerous distinct and interdependent components Every component has its own inherent protective value, and the final combination of them is likely to be related to an animal’s immunological history and evolutionary development Vertebrate immune system consists of both systemic and mucosal immune compartments, but it is the mucosal immune system which protects the body from the first encounter of pathogens According to anatomical location, the mucosa-associated lymphoid tissue, in teleost fish is subdivided into gut-, skin-, and gill-associated lymphoid tissue and most available studies focus on gut The purpose of this paper is to summarise the current knowledge of the immunological defences present in skin mucosa as a very important part of the fish immune system, serving as an anatomical and physiological barrier against external hazards Interest in defence mechanism of fish arises from a need to develop health management tools to support a growing finfish aquaculture industry, while at the same time addressing questions concerning origins and evolution of immunity in vertebrates Increased knowledge of fish mucosal immune system will facilitate the development of novel vaccination strategies in fish

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An Overview of the Immunological Defenses in Fish Skin

Publisher Summary This chapter describes the different aspects of metamorphosis and fish ontogeny. The term “metamorphosis,” when considered in the broadest sense in the animal kingdom, refers to any abrupt change in the form or structure of an organism during postembryonic development. A first metamorphosis occurs in all species having a larva period and is the phase that terminates this period and that leads into a juvenile period. Bony fishes with a classical first metamorphosis during their ontogeny are Anguilliformes, Elopiformes, Notacanthiformes, and Pleuronectiformes. First metamorphosis is also present in Petromyzontiformes, but not in Class Chondrichthyes or in Myxiniformes. A second metamorphosis may occur in many fish species when juveniles undergo sexual maturation to definitive adults, but it is not a true metamorphosis. The time of first metamorphosis varies among the orders of fishes, but is usually related more to body length than to age. Growth rate within a population may also be an important determinant. In species with a protracted and nontrophic metamorphic phase, physiological preparation is essential to the completion of metamorphosis.

2 First Metamorphosis

Lamprey and hagfish, the living representatives of jawless vertebrates, use genomic leucine-rich-repeat cassettes for the combinatorial assembly of diverse antigen receptor genes encoding variable lymphocyte receptors of two types: VLRA and VLRB. We describe here the VLRB-bearing lineage of lymphocytes in sea lamprey. These cells responded to repetitive carbohydrate or protein determinants on bacteria or mammalian cells with lymphoblastoid transformation, proliferation and differentiation into plasmacytes that secreted multimeric antigen-specific VLRB antibodies. Lacking a thymus and the ability to respond to soluble protein antigens, lampreys seem to have evolved a B cell-like system for adaptive humoral responses.

Antibody responses of variable lymphocyte receptors in the lamprey.

Vertebrate red Blood cells : , Vertebrate red Blood cells : , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Vertebrate red blood cells

Haemopoiesis has been studied throughout the life cycle of the parasitic lamprey, Lumpetra fluviatilis, with supplementary data being provided by its nonparasitic derivative, Lampetra planeri. Attention was paid to the location of the principal haemopoietic sites in both the larval and post-larval stages and to the mode of differentiation of the blood cells. In the prolarva, the formation of blood cells takes place initially in the blood islands but, at the time when the gut starts to rotate, this role is taken over by the typhlosole. After the ammocoete has reached about 20 mm in length, division and maturation of blood cells were also clearly detected in the intertubular and fat cell region of the nephric fold. Both the typhlosole and nephric fold discharge blood cells into the circulation and throughout the rest of larval life constitute the main sites of lymphopoiesis, erythropoiesis and granulopoiesis. At the beginning of transformation, however, both these structures undergo involution and by the end of metamorphosis the haemopoietic function has been assumed by the fat column. This latter organ remains active throughout the adult phase until near the end of the spawning run at which time it undergoes massive degenerative changes.

Differentiation of blood cells from the fixed cells of haemopoietic tissues occurs only in the blood islands of the prolarva and in the typhlosole during the very earliest stages of its development. Throughout the rest of the life cycle, the mode of formation of blood cells was the same in haemopoietic tissues containing a reticular network (typhlosole, fat cell region of the nephric fold and fat column) as in haemopoietic tissue where there was no such fibrous arrangement (the intertubular tissue of the more ventral regions of the opisthonephric kidney). Haemopoietic tissues could be seen to be formed in all the above structures by the accumulation of immature cells in tissue spaces which form a suitable environment for cell division and maturation. Descriptions are given of lineages leading from small lymphocyte-like stem cells to erythrocytes and to eosinophilic and neutrophilic granulocytes, and from large lymphocytes to macrophages.

Blood cell formation in the River lamprey, Lampetra fluviatilis

The morphology, development and physiology of blood cells

Supravital preparations of blood and haemopoietic tissues have been studied by interference contrast, phase contrast and conventional light microscopy to help identify the different categories of the smaller blood cells of lampreys. These methods were also used in conjunction with an examination of sectioned material and fixed blood films, to investigate macrophage activity by the blood cells and the liver Kupffer cells. The diameter of the smallest living blood cells was 4–5 |mUm. When these produced extensive clotting fibres, particularly in the presence of foreign substances, they were obviously thrombocytes, whereas others, some of which contained prominent nucleoli, were considered to represent small lymphocytes and stem cells. Slightly larger cells (5–6 |mUm), in which the nuclearcytoplasmic ratio was slightly lower and granules were being formed, represented the first stage in the formation of neutrophilic and eosinophilic granulocytes. The early members of the erythrocyte lineage could be distinguished from these early progranulocytes by their greater thickness under interference contrast microscopy and by their much more rapid degeneration and lack of amoeboid movement in blood films. All blood cells, apart from erythrocytes and differentiating cells of the erythrocyte series, showed amoeboid movement and many were capable of phagocytosing small particles. There was no evidence that, except for macrophages derived from lymphocyte-like cells, any free blood cells were capable of engulfing whole erythrocytes. During metamorphosis, phagocytic activity was very conspicuous in both blood cells and Kupffer cells, the latter of which exhibited pronouncedn erythrophagocytosis.

Further observations on the development and destruction of lamprey blood cells

Serial sections, injections with india ink and latex, and observations on fresh material, have been used to determine the pattern of blood circulation within the intestine of larval and adult lampreys. Attention has also been paid to resolving the variable terms previously applied to many of the blood vessels, and to the possible functional significance of the differences found between the two life cycle stages. In the larva, the main arterial supply to the intestine consists of a typhlosolar artery, while the venous return is comprised of a posterior and a left and right anterior intestinal vein that usually unite before entering the liver. Although a typhlosolar artery is also present in the adult, the main venous return of the ammocoete is replaced at metamorphosis by a newly formed typhlosolar vein. Moreover, in the ammocoete a considerable amount of blood is discharged into the haemopoietic sponge-work of the typhlosole and the arterial supply to the intestine is poorly developed. By contrast, the typhlosolar sponge-work is lost in the adult and a more efficient arterial supply is developed within the lamina propria of the various intestinal regions. Furthermore, vascular couples are developed in the adult which facilitate the flow of blood in opposite directions in the intestinal wall. Since, during both life cycle stages, the arterial blood passes into tissue spaces, there is no true capillary network in the intestine and no evidence was found for the presence of a lymphatic system. It is suggested that the changes which take place in the intestinal blood supply and the internal structure of the gut during metamorphosis result in improvements both to the vascular system and to the assimilation efficiency.

The intestinal blood circulation in the River lamprey, Lampetra fluviatilis

A brief account is given of the different arrangements of the heart and associated blood vessels of ammocoetes and adult lampreys, the significance of the oesophageal suspension in ammocoetes and the structure of the rigid cartilaginous pericardium which is developed during lamprey metamorphosis. These accounts have then been used, in conjunction with the size, shape and position of the apertures and recesses of the ossified pericardial capsule of the Devonian osteostracan Norselaspis glacialis, to reinterpret the way in which the heart chambers were arranged within this fossil agnathan and to elucidate the vessels responsible for returning blood to its heart. The dorsal aorta of osteostracans undergoes a similar right-hand curve just behind the postbranchial wall to that exhibited by the dorsal aorta of larval lampreys. This indicates that the dorsal aorta of N. glacialis was likewise shifted to the right by vertical strands of connective tissue which suspend the oesophagus from the under surface of the notochord and between two ducts of Cuvier and the heart. The size and shape of apertures and recesses in the pericardial cavity of Norselaspis glacialis supports the view that, in this osteostracan, two ducts of Cuvier entered the pericardial cavity through a dorsal opening on the posterior part of the capsule and then joined with the sinus venosus. The marginal sinuses/veins in the anterior part of the body of N. glacialis, from which blood passed horizontally into the respective ducts of Cuvier, are now regarded as homologues of the anterior cardinal veins. While there is evidence that, as in ammocoetes, the right duct of Cuvier was larger than the left duct in N. glacialis, the relative size and position of its proposed atrium and ventricle was apparently more like that of adult lampreys. Despite differences in the mode of formation of the ossified pericardium of osteostracans and the cartilagenous pericardium of adult lampreys, these structures presumably had a similar function. This would involve generating negative pressure within the pericardial chamber during ventricular systole, thereby aiding atrial diastole and thus the influx of blood into the heart from the main venous vessels, such as the inferior jugular vein(s) and the ducts of Cuvier. The inner side of the pericardial capsule of osteostracans, like that of adult lampreys, appears to have possessed an extensive vascular network which could thus have likewise played an important role in providing fluid for lubricating the surface of the heart.

The arrangement of the heart chambers and associated blood vessels in the Devonian osteostracan Norselaspis glacialis.A reinterpretation based on recent studies of the circulatory system in lampreys

Lord Richard Percy

Papers

Blood cell formation in the River lamprey, Lampetra fluviatilis

The morphology, development and physiology of blood cells

Further observations on the development and destruction of lamprey blood cells

The intestinal blood circulation in the River lamprey, Lampetra fluviatilis

The arrangement of the heart chambers and associated blood vessels in the Devonian osteostracan Norselaspis glacialis.A reinterpretation based on recent studies of the circulatory system in lampreys