PhD thesis - Biologisk Institut - KÃ¸benhavns Universitet

More documents

Recommendations

Info

Abstract 10AbstractPeanut worms (Sipuncula) have been variously related to a number of animals in thepast, but, recently, and despite their non-segmented adult body, molecularphylogenetic analyses place them within Annelida. In order to contribute to thequestion whether or not sipunculan worms show traces of a segmental pattern in theirontogeny, neuro- and myogenesis as well as the distribution of proliferating cells wereanalysed in three different sipunculan species. The data show that the rudiments ofnumerous circular muscles of the body wall musculature and the longitudinal retractormuscles appear at the same time in the early trochophore larva. In addition,throughout development newly formed ring muscles emerge along the entire anteriorposterioraxis by fission from already existing myocytes. In contrast to that,neurogenesis does follow a segmental pattern by subsequently emerging pairs ofserotonergic perikarya along the anterior-posterior axis, which are associated with apaired ventral nerve cord and are arranged in four distinct repetitive units. Thismetameric pattern, however, disappears prior to metamorphosis and the ventral nervecords fuse to form the single ventral nerve of the adult. Congruently, the distributionpattern of mitotic cells show similarities to an annelid-like posterior growth zone thatalso disappears in metamorphic competent pelagosphera larvae. Accordingly, thesedevelopmental and morphological data corroborate recent molecular analyses andshow that sipunculans stem from a segmented ancestor. Furthermore, the loss ofsegmentation in these relatively large, free living animals indicates that bodysegmentation may easier be lost during evolution than previously assumed. Theontogenetic establishment and (secondary) loss of segmentation renders Sipunculaideal for developmental and evolutionary studies on the segmentation process inMetazoa.
11 Short abstractShort abstractIn this <strong>PhD</strong> <strong>thesis</strong>, three sipunculan species were investigated byimmunocytochemistry in conjunction with confocal laserscanning microscopy and 3Dreconstruction software, in order to clarify whether or not cryptic segmentation can befound during sipunculan ontogeny. The results show that sipunculan myogenesis doesnot follow a segmental manner, but for a short period of time neurogenesis and thedistribution of mitotic cells show transitional stages of segmentation duringsipunculan development, thus supporting a sipunculan/annelid affiliation. Moreover,the establishment of an in situ hybridisation protocol for the model sipunculanThemiste pyroides for gene expression analyses pave the way for future studies on themolecular processes underlying sipunculan segmentation that might give importantinsights into the evolution of segmentation.
Page 2 and 3: 2DEPARTMENT OF BIOLOGYFACULTY OF SC
Page 4 and 5: 4“In a world that keeps on pushin
Page 6 and 7: Acknowledgements 6AcknowledgementsI
Page 8 and 9: Content 8ContentPreface…………
Page 12 and 13: General introduction 12General intr
Page 14 and 15: General introduction 14tuft and a r
Page 16 and 17: Thesis objectives 16In the followin
Page 18 and 19: Material and methods 18Nacka, Swede
Page 20 and 21: Material and methods 20Table 3. Iso
Page 22 and 23: Material and methods 221 hr in 1% b
Page 24 and 25: Results 24Figure 3. Expression of m
Page 26 and 27: Results 26Figure 4. Confocal microg
Page 28 and 29: Results 28positioned to the ventral
Page 30 and 31: Results 30developed cerebral gangli
Page 32 and 33: General discussion 32alveolata, and
Page 34 and 35: General discussion 34the sipunculan
Page 36 and 37: General discussion 36exhibit an add
Page 38 and 39: Conclusions and future perspectives
Page 40 and 41: References 40Dordel J, Fisse F, Pur
Page 42 and 43: References 42Hunnekuhl VS, Bergter
Page 44 and 45: References 44Rice ME. 1975b. Observ
Page 46 and 47: References 46Voronezhskaya EE, Nezl
Page 48 and 49: Current Biology 18, 1129-1132, Augu
Page 50 and 51: Segmental Neurogenesis in Sipuncula
Page 52 and 53: Chapter III 52Chapter IIIWanninger
Page 54 and 55: Sipunculans and segmentationdevelop
Page 56 and 57: Sipunculans and segmentationof one
Page 58 and 59: RESEARCH ARTICLECellular and Muscul
Page 60 and 61:
SIPUNCULAN GROWTH PATTERNS 3Denmark
Page 62 and 63:
SIPUNCULAN GROWTH PATTERNS 5either
Page 64 and 65:
SIPUNCULAN GROWTH PATTERNS 7Figure
Page 66 and 67:
SIPUNCULAN GROWTH PATTERNS 9Develop
Page 68 and 69:
SIPUNCULAN GROWTH PATTERNS 11Hydroi
Page 70 and 71:
SIPUNCULAN GROWTH PATTERNS 13de Ros
show all

PhD thesis - Biologisk Institut - KÃ¸benhavns Universitet

Create successful ePaper yourself

Delete template?

Save as template?