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Results and discussion 23 of four classically defined subgroups of the Pax family transcription factors (Balczarek et al. 1997). Pax3/7 shares its expression among distantly related insects and shows several patterns including pair-rule, segment polarity, and neural patterning (Davis et al. 2005). In crustaceans Pax3/7 genes are expressed in iterated stripes (Davis et al. 2005). In myriapods and chelicerates Pax3/7 gene expression exhibits iterated stripes that form early in the posteriormost part of the germ band (Davis et al. 2005). In the tardigrade Hypsibius dujardini, the Pax3/7 proteins localize in a segmentally iterated pattern in the ectoderm, after establishment of endomesoderm segmentation, but before the visible segmentation of the ectoderm (Gabriel and Goldstein 2007). Pax3/7 is also localized within the developing head region of the tardigrade embryo, but no pair-rule pattern is visible during any stage of embryogenesis (Gabriel and Goldstein 2007). Tardigrades, together with arthropods and onychophorans belong to Panarthropoda (Halanych 2004).The expression pattern of Pax3/7 in H. dujardini suggests that the pair-rule function of Pax3/7 may have arisen near the base of Arthropoda. In the annelid Platynereis dumerilii Pax3/7 proteins are found in the peripheral nervous system (Kerner et al. 2009). In larvae of the brachiopod Terebratalia transversa DP311 and DP312 show identical staining patterns. Pax 3/7 starts to be present in four cells of the apical lobe in the late elongated gastrula (Fig. 4B). The cells containing Pax3/7 products are later distributed in a ring on the apical lobe of early three-lobed larvae without setae (Fig. 4C). Fully established larvae show a loose distribution of cells that contain Pax3/7 products in their apical lobe (Fig. 4D, E). In juveniles Pax3/7 containing cells are mainly found in the growing lophophore (Fig. 4F). The presence of Pax3/7 gene products in the apical lobe indicates a function of those genes during neurogenesis in T. transversa. However, further experiments are necessary in order to assess whether the staining specifically shows Pax3/7 protein products, since the antibodies used were developed against the Pax3/7 sequences of Drosophila melanogaster. Ideally, cloning of the sequences of the Pax3/7 homologs of Terebratalia transversa should be carried out, followed by mapping of the epitopes of DP311 and DP312 on peptide arrays with the known peptide sequences of T. transversa and other metazoans (Harlow and Lane 1999). The final proof would then be in situ hybridizations with the specific corresponding probes. In addition, a double staining with serotonin would be necessary in order to prove that the cells containing Pax3/7 gene products are co-localized with the nervous system.
24 Results and discussion Growth patterns of Terebratalia transversa Figure 4. Staining of Pax3/7 proteins with DP311. Overlay of confocal maximum projections on light micrographs. Anterior is up and scale bars equal 50 µm. (A) Gastrula with blastopore (asterisk) and no signal. (B) Late gastrula with slit-like blastopore (asterisk). Pax3/7 proteins are stained in four cells in the future apical lobe (al). (C) Early three-lobed larva with almost closed blastopore (asterisk). Pax3/7 proteins are present in several cells of the apical lobe (al) and distributed in a ring around it. No signal is found in the mantle lobe (ml) and in the pedicle lobe (pl) (D) Lateral view of a larva with apical lobe (al), mantle lobe (ml), pedicle lobe (pl), and setae (se). Pax3/7 protein containing cells are concentrated in the dorsal part of the apical lobe. (E) Fully established larva with apical lobe (al), mantle lobe (ml), pedicle lobe (pl), and setae (se). Cells with Pax3/7 proteins are loosely distributed in the apical lobe. (F) Juvenile after metamorphosis. Pax3/7 proteins are loosely expressed in the developing lophophore (Lo) of the juvenile. The dorsal shell (s) of this specimen is slightly shifted upwards relative to its natural position, and larval setae (se) extend out of the valves In order to identify possible growth zones in brachiopod larvae, proliferating cells in Terebratalia transversa were labeled with 5-bromo-2-deoxyuridine (BrdU). Dividing cells are equally distributed in the blastula stage (Fig. 5A), the gastrula (Fig. 5B), and the elongated gastrula (Fig. 5C). In the elongated gastrula, cells divide mostly in the center of the larva and form the mantle lobe, which is marked by a ring of dividing cells (Fig. 5D). Thereafter, dividing cells are again equally distributed throughout the larva (Fig. 5E). Larvae competent for metamorphosis also show an equal distribution of proliferating cells after a pulse-chase experiment, which once again indicates that there are no distinct growth zones that form most parts of the larval body, but that dividing cells are found throughout the developing specimen (Fig. 5F). The BrdU data suggest that from the viewpoint of proliferation zones, there are no similarities between
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: 22 Results and discussion Wanninger
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
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74 Submitted manuscript Chapter IV
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PhD thesis

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