dc.description.abstract | In Metazoa the maintenance of individuality and the defense against pathogens is
devolved to the molecular mechanisms of the innate immunity. Adaptive immunity
complements innate immunity in gnathostome vertebrates, thus indicating an increase of
specialization of the defense mechanisms in the course of evolution. The Urochordate
Ciona intestinalis, as the other invertebrates, does not have a gnathostome-type adaptive
immune system, but, for its phylogenetic position, represents an excellent model for a
comparative study of the elements and of the possible evolutionary pathways that led to
the assembly of the adaptive system.
As in other organisms, also in Ciona the blood cells have fundamental roles in immune
defense, such as phagocytosis, encapsulation and release of substances with proinflammatory
activity and in this context the understanding of their nature and function
is fundamental. Despite the data collected in the last decades, many issues about blood
cells in Ciona, as in other tunicates, remain still open. In particular, essential
information about their embryonic and adult origin, their differentiation and even their
precise classification, is still scanty, thus leaving the problem of blood cells genesis and
homeostasis, also during immune reaction, unsolved. The project is aimed to the study
of genes directly involved in hemocyte differentiation that may represent possible
markers for the identification of hematopoietic sites. To this aim, genes that are
involved in hematopoiesis in other organisms, such as Bmi, Ikaros, PU.1, Numb and
GATA-a have been identified, sequenced, and characterized using PCR, in situ
hybridization and immunochemistry during the post metamorphic stages and in the
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adult tissues of C. intestinalis. Among these genes the C. intestinalis homolog of the
Numb gene, involved in asymmetric cell division in mammals, has been identified as a
possible marker for the study of hematopoiesis. The study of Ci-Numb provides
preliminary information that helps in the understanding of hematopoietic processes of
both the post-metamorphic and adult animal, and points out some previously
undescribed aspects of the pharynx structure. In fact, the expression data produced at
post-metamorphic stages and in the adult indicate that both the Ci-Numb transcripts and
the protein are present in discrete regions of the animal body. These overlap with sites
of proliferative activity and, more interestingly, with some of the regions previously
indicated as hematopoietic. The morphological study at ultrastructural level of the
tissues expressing Ci-Numb, in the juvenile as also in the adult, has allowed a more
detailed characterization of the cell types that populate the hematopoietic sites.
Morphological analysis of the structures of the adult pharynx, and of the stigmata in
particular, show that the hematopoietic areas, described as compact groups of cells
adjacent to the pharynx epithelium, correspond to the some cells that form the structure
of the stigmas. This leads to a reassessment of the data that refer to the hematopoietic
sites as “nodules” in the body wall adjacent to the muscle. The electron microscopy
observations carried out in the juveniles demonstrate for the first time the genesis of the
stigma.
In conclusion, Ci-Numb can be considered a good marker of early hematopoiesis and
may represent a baseline for further observations. | en_US |