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Chapter IV Submitted manuscript 71 shows 73% -80% sequence similarity with Cdx/caudal protein sequences known from other metazoans and 61% sequence similarity with the Cdx/Xlox sequence of Nematostella vectensis (Fig. 2). The TtrCdx segment cloned by RACE PCR was 1037 base pairs long and is deposited in GeneBank under the accession number XXXX. The transcribed region downstream of the homeobox ends with a poly-A tail and shows no similarity to other known gene sequences. Not and Cdx expression during Terebratalia development Cleavage in Terebratalia transversa is radial. Within eight hours after fertilization (hpf), the embryo develops into a blastula. Gastrulation starts at 18 hpf. The spherical gastrula has a central blastopore until approximately 26 hpf. Thereafter, the gastrula elongates and the blastopore narrows to a slit, moves anteriorly, and closes at around 42 hpf. At this stage, the elongated larva starts to develop its characteristic three– lobed body, consisting of an anterior lobe, a mantle lobe, and a pedicle lobe. At around 65 hpf, the larval setae start to form and larval development is complete by approximately 80-96 hpf. Under our experimental conditions, larvae settled between 120 and 240 hpf. The expression patterns of TtrNot and TtrCdx are shown in Figs. 3–5. Fertilized eggs and early cleavage stages did not reveal the presence of a TtrNot RNA transcript (Fig. 3A-C). Expression of TtrNot starts laterally on both sides of the blastopore in the early gastrula stage at 18 hpf (Fig. 3D). At 22 hpf, the expression of TtrNot increases in the ectoderm on both sides of the blastopore and extends towards the animal pole of the gastrula (Figs. 3E, F, 5A). These lateral bands of TtrNot expressing cells fuse in slightly older stages (i.e., at 24 hpf; Fig. 3G). Shortly after that, at 26 hpf, when the archenteron is enlarged, the band of TtrNot expressing cells on the animal pole narrows (Figs. 3H, 5B). At 28 hpf the blastopore starts to become slit-like, the gastrula elongates, and TtrNot expressing cells are present in two fields lateral of the blastopore and close to the future anterior pole of the larva. The fields of TtrNot expressing cells are interconnected by a narrow band of TtrNot expressing cells on the animal side (Figs. 3I-K, 5C). At around 36 hpf the blastopore starts to close, the larva elongates further, and TtrNot expressing cells are only detected in the animal region of the gastrula, which later forms the larval apical lobe (Fig. 3L). Subsequently, the blastopore closes completely and the larva differentiates the three characteristic body lobes. TtrNot is continuously expressed in a ring of cells in the apical lobe until the beginning of setae formation. The area of the apical lobe where TtrNot is expressed corresponds to the region that bears the cilia used for swimming of the larva (Figs. 3M, N, 5D). Once the larval lobes are fully established and setae formation has started (i.e., at around 75 hpf), TtrNot is no longer detectable (Figs. 3O, 5E). Likewise, specimens that have settled and started to metamorphose do not show any TtrNot expression (Figs. 3P, 5F). TtrCdx starts to be expressed in the ectoderm of the gastrula at the posterior pole of the blastopore (Figs.
72 Submitted manuscript Chapter IV Fig. 5 Schematic representation of Not and Cdx expression in Terebratalia transversa. Dark grey – ectoderm, light grey – endoderm. All specimens are approximately 120 µm in diameter. (A) Almost spherical gastrula at 22 hours after fertilization (hpf). TtrNot is expressed in two lateral fields of the ectoderm. TtrCdx is expressed on the posterior side of the blastopore. (B) Gastrula at 26 hpf. The two lateral fields of TtrNot expressing cells are interconnected by a narrow band of TtrNot expressing cells on the animal side of the gastrula. TtrCdx is more intensely expressed posterior to the blastopore. (C) Early larva at 30 hpf. The fields of TtrNot expressing cells are positioned further towards the animal pole of the gastrula than in previous stages. The blastopore is still open. TtrCdx is expressed posterior to the blastopore. (D) Larva at the onset of lobe formation at 42 hpf. TtrNot is solely expressed in the posterior part of the apical lobe. Locomotory cilia and an apical tuft are already present. TtrCdx is expressed in the postero-ventral part of the mantle lobe. (E) Three-lobed larva at 75 hpf. TtrNot is no longer expressed but TtrCdx is still present in the posterior part of the mantle lobe. (F) Juvenile at 360 hours after settlement. The lophophore has started to develop between the valves. Neither TtrNot nor TtrCdx are expressed. 4A, 5A). TtrCdx expression remains in this position in the larval ectoderm throughout development. Expression intensifies as the gastrula gets older (Figs. 4B, C, 5B). In early larvae prior to the onset of lobe formation (Figs. 4D, 5C), early three-lobed larvae (Figs. 4E, 5D), and fully developed larvae (Figs. 4F, 5E) TtrCdx is expressed in the ventral ectoderm posterior to the closed blastopore. Neither the expression of TtrNot nor the expression of TtrCdx is co-located with the larval serotonergic nervous system of Terebratalia transversa, which comprises an apical organ with eight flask-shaped serotonergic cells that lie antero-dorsally in the apical lobe (Fig. 5). The flask-shaped cells are connected via individual neurites to a larval neuropil that is situated in the center of the apical lobe. (Fig. 5A,
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Comparative neurogenesis, muscle de
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2 Principal supervisor Assoc. P
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4 Preface This thesis presents
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6 Abstract Brachiopods are a sm
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8 Acknowledgements The endeavou
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10 Introduction Nervous system Micr
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12 Material and methods Material an
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14 Material and methods purpuratus,
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16 Results and discussion Results a
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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 71: 70 Submitted manuscript Chapter IV
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