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Evolution of the secondary sensory cells in tunicates and their development in Ciona intestinalis
Full text linkThis thesis attempts to clarify the evolution of secondary sensory cells in Tunicata (Chordata), the Vertebrata sister group, to study these cells in species belonging to different classes using a morphological approach, and to gain insights into their development using a molecular approach based on important developmental genes.
In chapter 1, we analysed the mouth of three species of Thaliacea, representative of the three orders, to verify the presence of secondary mechanoreceptors comparable with the ones in the coronal organ described in the Ascidiacea class. We showed that oral secondary sensory cells are present with the exception of one species. We hypothesised that the presence of these cells in the oral region is related to the animal feeding mechanism. In chapter 2, we extended the morphological study to the class Appendicularia. These species are known to possess an oral sensory organ, the circumoral ring, composed of secondary sensory cells. We described these cells in detail, thus completing the data collection of the main tunicate groups. Moreover, based on these results and data from the literature, we performed a cladistics analysis using the cephalochordate amphioxus and vertebrates as outgroups. Our research showed that all tunicate secondary sensory cells may have evolved from a monociliated prototype, which successively differentiated into the present variety of secondary sensory cells.
Chapter 3 describes the development of the oral secondary sensory structures in the model Ciona intestinalis (Ascidiacea). In this animal, we found that secondary sensory cells after the metamorphosis could be identified as cells with short cilia and microvilli, which later become pluriciliated. Moreover, we have provided evidence that secondary sensory cells can proliferate during development. Finally, chapter 4 shows that some genes involved in neural and sensory cell differentiation in vertebrates (Notch, Delta, Hairy/Hes, Atoh, Musashi) and other molecules implicated in neurotransmission (TRP channels and glutamate) are expressed in the secondary sensory cells of C. intestinalis.
Taken together, the results presented in this thesis confirm that secondary sensory cells are a common feature of tunicates and have an important role as mechanoreceptors, likely playing a role in the feeding process. Moreover, our data suggest that important genes involved in the differentiation and function of these cells might have been present in the common ancestor of tunicates and vertebrates. Thus, these cells represent a plesiomorphic feature in these two groups
Coronal organ development: in search of the hair cell ancestor in the ascidian Ciona itnestinalis (Tunicata, Chordata)
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Morphological differentiation of the ascidian coronal organ and molecular characterization of its secondary sensory cells
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Cytodifferentiation of hair cells during the development of a basal chordate
Full text linkTunicates are unique animals for studying the origin and evolution of vertebrates because they are considered vertebrates' closest living relatives and share the vertebrate body plan and many specific features. Both possess neural placodes, transient thickenings of the cranial ectoderm that give rise to various types of sensory cells, including axonless secondary mechanoreceptors. In vertebrates, these are represented by the hair cells of the inner ear and the lateral line, which have an apical apparatus typically bearing cilia and stereovilli. In tunicates, they are found in the coronal organ, which is a mechanoreceptor located at the base of the oral siphon along the border of the velum and tentacles and is formed of cells bearing a row of cilia and short microvilli. The coronal organ represents the best candidate homolog for the vertebrate lateral line. To further understand the evolution of secondary sensory cells, we analysed the development and cytodifferentiation of coronal cells in the tunicate ascidian Ciona intestinalis for the first time. Here, coronal sensory cells can be identified as early as larval metamorphosis, before tentacles form, as cells with short cilia and microvilli. Sensory cells gradually differentiate, acquiring hair cell features with microvilli containing actin and myosin VIIa; in the meantime, the associated supporting cells develop. The coronal organ grows throughout the animal's lifespan, accompanying the growth of the tentacle crown. Anti-phospho Histone H3 immunostaining indicates that both hair cells and supporting cells can proliferate. This finding contributes to the understanding of the evolution of secondary sensory cells, suggesting that both ancestral cell types were able to proliferate and that this property was progressively restricted to supporting cells in vertebrates and definitively lost in mammals
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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