PhD thesis

More documents

Recommendations

Info

Chapter IV Submitted manuscript 73 Fig. 6 Larval serotonergic nervous system of Terebratalia transversa. Maximum projections of a confocal microscopy image stack. Serotonin is labeled red, tubulin is green, cell nuclei are blue. (A) Lateral view of a fully established larva with apical lobe (al), mantle lobe (ml), and pedicle lobe (pl). The apical organ comprises eight flask-shaped cells (arrows) which are connected by neurites (empty arrowheads) to a larval anterior neuropil (asterisk). The apical organ is situated towards the dorsal side of the apical lobe. Note that only cilia but no neural structures are labeled by the α-tubulin antibody. (B) Detailed view of the apical organ of the specimen shown in A. The apical organ comprises two sets of four flask-shaped cells each (arrowheads). The flask-shaped cells are connected to the neuropil (asterisk) by individual neurites (empty arrowheads). B). Staining with the pan-neural marker anti-acetylated tubulin did not reveal any additional neural structures. DISCUSSION The role of the Not gene in metazoan neurogenesis The designation of the gene “Not” refers to the site where its expression was detected for the first time, namely in the notochord of the African Clawed Frog, Xenopus laevis (Gont et al. 1993, von Dassow et al. 1993). The notochord is a cartilaginous, rod shaped structure, apomorphic to the Chordata. It is at least present in some developmental stages of all chordates, including the ascidian tadpole larva, and functions as axial skeleton, induces the development of the neural tube, and is thus a key player in chordate neurogenesis (Stemple 2005). Moreover, Not is expressed in the neural tube of the mouse, chick, frog, and zebrafish (Stein and Kessel 1995, Talbot et al. 1995, Yasuo and Lemaire 2001, Beckers et al. 2007). Where it has been analyzed in detail, Not seems to act primarily as a transcriptional repressor (Yasuo and Lemaire 2001). In zebrafish, loss-offunction mutants of floating head (flh; the zebrafish Not homolog) lack the notochord altogether, and the somites fuse below the neural tube (Talbot et al. 1995). Expression studies suggest that cells lacking flh expression differentiate into muscle rather than notochordal tissue (Halpern et al. 1995). Noto, the Not homolog in the mouse, and flh repress paraxial mesoderm fate while maintaining axial mesoderm fate (Amacher and Kimmel 1998). Only little is known about the expression patterns and functions of Not in non-chordate metazoans. In Trichoplax adhaerens, the Not gene is expressed at the bottom of body folds of intact animals as well as during wound healing (Martinelli and Spring
74 Submitted manuscript Chapter IV 2004). In addition, Not expressing cells in this species, which lacks a nervous system and even neurons, overlaps with the site of expression of the neurotransmitter RFamide (Schuchert 1993). In Drosophila, the Not homolog 90Bre is present in the nervous system, where it is expressed in the ventral nerve cord and the posterior brain anlage of germ band retracted embryos, as well as in the lateral/ posterior region of the eye/antennal disc (Dessain and McGinnis 1993). In the ascidians Halocynthia roretzi and Ciona intestinalis, Hr-Not and Ci- Not, respectively, are expressed in the posterior end of the tail, as well as in the notochord and a small part of the anterior neural tube in the larval tailbud stage (Utsumi et al. 2004). These data hint towards an ancestral role of Not in metazoan neurogenesis. The ring-like expression of TtrNot in the ciliated region of the apical lobe in Terebratalia larvae is intriguing. Noto, the Not ortholog in the mouse, is known to function in ciliogenesis, and TtrNot might thus serve a similar role in our study species. In this context,it should also be considered that the putative spiralian homolog of this larval swimming device, the prototroch, is underlain, and probably innervated, by a ring nerve (Wanninger 2009). Accordingly, it is tempting to speculate that Not may also be expressed in the prototroch ring nerve of spiralian trochophore larvae and/ or the prototroch itself. In Terebratalia transversa, however, we did not find any corresponding neural structure in the region of Not expression (Fig. 6). The larval nervous system of T. transversa differs in several details from that of the craniiform brachiopod Novocrania anomola. In N. anomala, the apical organ comprises four, centrally positioned serotonergic flaskshaped cells that are connected to two ventral neurites which elongate laterally along the larval body (Altenburger and Wanninger 2010). By contrast, the apical organ of T. transversa has two sets of flask-shaped cells. Each set contains four cells and each cell is connected to the larval anterior neuropil by a single serotonergic neurite. Due to these differences, the morphology of the ancestral brachiopod larval apical organ remains elusive. However, the data currently available indicate that an apical organ comprising serotonergic flask-shaped cells was part of the brachiopod ground pattern and most likely constitutes a morphological apomorphy of Lophotrochzoa, since such cells are also found in larval Entoprocta, Mollusca, Nemertea, Annelida, and Ectoprocta (Pires and Woollacott 1997, Shimizu et al. 2000, Friedrich et al. 2002, Voronezhskaya et al. 2002, 2003, McDougall et al. 2006, Wanninger et al. 2007, Fuchs and Wanninger 2008, Chernyshev and Magarlamov 2010, Nielsen and Worsaae 2010). Not expression during gastrulation and germ layer formation In all species studied so far, Not expression starts prior to or at the onset of gastrulation. This is also the case in the brachiopod investigated herein, Terebratalia transversa. In the sea urchin Strongylocentrotus purpuratus, Not is expressed in the vegetal plate at the mesenchyme-blastula stage and in the secondary mesenchyme, with
Page 1 and 2:
Comparative neurogenesis, muscle de
Page 3 and 4:
2 Principal supervisor Assoc. P
Page 5 and 6:
4 Preface This thesis presents
Page 7 and 8:
6 Abstract Brachiopods are a sm
Page 9 and 10:
8 Acknowledgements The endeavou
Page 11 and 12:
10 Introduction Nervous system Micr
Page 13 and 14:
12 Material and methods Material an
Page 15 and 16:
14 Material and methods purpuratus,
Page 17 and 18:
16 Results and discussion Results a
Page 19 and 20:
18 Results and discussion posterior
Page 21 and 22:
20 Results and discussion Myogenesi
Page 23 and 24: 22 Results and discussion Wanninger
Page 25 and 26: 24 Results and discussion Growth pa
Page 27 and 28: 26 Results and discussion argument
Page 29 and 30: 28 References References Abdelkhale
Page 31 and 32: 30 References priapulids and protos
Page 33 and 34: 32 References James, M. A., Ansell,
Page 35 and 36: 34 References regionalization, prol
Page 37 and 38: 36 References 211. Williams, A., Ca
Page 39 and 40: 38 Chapter II Frontiers in Zoology
Page 53 and 54: 52 Chapter III Chapter III Altenbur
Page 55 and 56: 54 Chapter III Altenburger and Wann
Page 63 and 64: 62 Chapter IV Chapter IV Altenburge
Page 65 and 66: 64 Submitted manuscript Chapter IV
Page 73: 72 Submitted manuscript Chapter IV
show all

PhD thesis

Create successful ePaper yourself

Delete template?

Save as template?