1,721,151 research outputs found
: A key species for evolutionary developmental studies
Full text linkI discovered tunicates while attending classes of Comparative Anatomy of Vertebrates as a Biology student at the University of Padua, Italy. I was fascinated by the evolutionary developmental (evo-devo) approach while I was analyzing vertebrate adaptations looking at their sister group, the simple tunicates. I graduated in 1988 and subsequently entered my university's graduate program in Bioscience. In 1993, I obtained my PhD Degree in Evolutionary Biology. I owe a great debt of gratitude to my mentors, Prof. Paolo Burighel and Prof. Giovanna Zaniolo, who instilled in me a passion for tunicate research, a rigorous scientific working method, and above all a commitment to intellectual honesty in interpreting literature-based results, which I consider their most important lesson. In 1998, I became a junior faculty in my University, and in 2010 I was promoted to associate professor. Currently, I teach Comparative Anatomy of Vertebrates and Eco-Evo-Devo and I am a member of the faculty of the graduate school in Biosciences. Over the course of 25 years of my academic life, I have had the opportunity to work as visiting scientist at the Universitè Paris XI (France), at the Friday Harbor Laboratories of the University of Washington (USA), and at Stanford University (USA). I have been also collaborating with members of the global tunicate research community and enjoy meeting them at the biannual International Tunicate Meetings
Stem cells in sexual and asexual reproduction of Botryllus schlosseri (Ascidiacea, Tunicata).
No full textEpigenetics in tunicates.
No full textTunicates are marine animals close to vertebrates, and have the ability, unique among chordates, to form large colonies of clonal individuals. Among tunicates, the most frequently studied ascidians represent an ideal model for investigating aspects of epigenetics evidenced during the various phases of the life-cycle. Interestingly, the typical mosaic development of eggs and embryos of ascidians, considered as a classic example of autonomous genetic control of genes for specification of cell lineage, may now be interpreted in the light of cytoplasmic and extracellular influences on the regulation of gene activity. In addition, the capacity of several species to create similar individuals by means of two different developmental pathways - embryogenesis and blastogenesis - and the high regulative power shown by colonies in natural or experimental modifications of the environment, reveal the importance of the epigenetic phenomena (interactions) during the entire life cycle of these animals. Two species are of particular importance as models, the solitary Ciona intestinalis (whose genome has been recently sequenced) and the colonial Botryllus schlosseri. We report here examples of epigenetic phenomena in ascidians, to show that the various stages of the entire development of the phenotype are driven by a dynamic interplay of genome, cellular components and tissues, and their micro- and macro-environment
Common and divergent pathways in alternative developmental processes of ascidians
Full text linkColonial ascidians offer opportunities to investigate how developmental events are integrated to generate the
animal form, since they can develop similar individuals (oozooids from eggs, blastozooids from pluripotent
somatic cells) through very different reproductive processes, i.e. embryogenesis and blastogenesis. Moreover,
thanks to their key phylogenetic position, they can help in the understanding of the molecular mechanisms of
morphogenesis and their evolution in chordates. We review organogenesis of the ascidian neural complex
comparing embryos and buds in terms of topology, developmental mechanisms and terminology. We propose
a new interpretation of bud territories, and reconsider nervous system development based on recent results
suggesting that ascidians have vertebrate placodal and neural-crest-like cells. Comparing embryonic and blastogenic
development in Botryllus schlosseri, we propose that the bud has territories with a placodal potentiality,
suggesting that chordate ancestors possessed neurogenic placodes, and that the genetic pathways regulating
neurogenic placode formation were co-opted for new developmental processes, such as blastogenesis
Ultrastructure and histochemistry of the testiculal efferent duct system and spermiogenesis in Opistognathus whitehurstii (Teleostei, Trachinoidei).
No full textTestis organization and spermatogenesis, with the emphasis on spermiogenesis, in Opistognathus whitehurstii are described by ultrastructural and histochemical methods. The germinal epithelium is extremely reduced and restricted to the periphery of the testis, while most of the organ is occupied by a highly developed system of testicular efferent ducts. A semicystic type of spermatogenesis is observed and in the germinal epithelium spermatogenesis occurs only until the spermatidal stage. Young spermatids are released into the lumen of the testicular lobules and mature to sperm within the efferent duct system. The epithelial cells of these ducts are involved in protein and glycogen secretion and in phagocytosis of degenerating germ cells and residual bodies cast off by developing spermatids. On the basis of these functions, the testicular efferent duct system cells are considered to be homologous to the Sertoli cells. A correlation between a highly developed testicular efferent duct system and semicystic spermatogenesis is examined and a possible functional meaning of this apparently unusual mode of sperm production is proposed
The juxtatesticular body of Jawfishes (Teleostei:Opistognathidae):comparative morphology and fine structure.
No full textA peculiar gland, the juxtatesticular body (JTB), ductless and consisting of follicles, had previously been discovered in males of two Opistognathus species (Teleostei, Opistognathidae). In this paper, we describe (1) the general morphology of the JTB in an additional two Opistognathus species, O. aurifrons and O. macrognathus, comparing it with that of the previously described species, and (2) the fine structure of the JTB of Opistognathus whitehurstii and O. maxillosus. Interspecific variability occurs both in the general organization of this gland and in the number of follicular cells. Fine structural analysis of the JTB, both in O. whitehurstii and O. maxillosus, reveals strong similarities with thyroid follicular cells, suggesting a similar pattern of synthesis and secretion. JTB follicular cells are arranged as a monolayered epithelium that surrounds a follicular lumen; they show a polarity in organelle distribution and membrane specialization typical of secreting cells. On the basis of their cytological and histochemical characteristics we propose that JTB follicular cells perform two major types of secretory activities: the secretion of a glycoprotein from the apical part of the cells into the follicular lumen and the endocrine, or paracrine, secretion of a still unknown substance(s) from the basal part of the cell either into the extrafollicular space or the blood or both. A hypothesis concerning the functional cycle of JTB follicle is also discussed
Regeneration ability in four stolidobranch ascidians: Ecological and evolutionary implications
No full textOvulation and embryo-parent relationships in Botrylloides leachi (Ascidiacea).
Full text linkThe ultrastructural events of ovulation and differentiation of the brood pouch are studied in the colonial ascidian Botrylloides leachi. Each zooid matures one or two yolked oocytes enveloped by test cells, vitelline coat, and inner and outer follicle cells. A small vesicular oviduct lies between the outer follicle cells and the brood pouch, a flask-shaped structure differentiated from the wall of the atrial chamber. The oviduct epithelium fuses with the outer follicle and brood pouch cells and breaks, creating a pathway which drives the oocyte to the brood pouch. Embryos develop in isolation in the latter whose epithelium undergoes differentiation: the cell surface increases enormously, forming deeper and deeper baso-lateral foldings, cell interdigitations and apical polymorphic protrusions. Extended tight junctions separate the different domains of the plasmalemma and create a barrier between the pouch lumen and the blood. Large quantities of glycogen, mainly in the form of rosettes, are formed and accumulate progressively in extensive apical regions. Glycogen, presumably released by apocrine secretion, fills the space between the brood pouch epithelium and the inner follicle cells surrounding the embryo. All features are indicative of a transfer of substances from the blood toward the embryo. The significance of the embryo-parent exchange in B. leachi and comparative aspects of ovoviviparity and viviparity in ascidians are discussed
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