Browsing by Subject "Aktin-Zytoskelett"

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Deskriptive und funktionelle Analyse der Mitglieder der Calponin-Genfamilie Xclp1, Xclp2 und Xclp3 während der Embryonalentwicklung von Xenopus laevis
(2008) Schmalholz, Silke; Blum, Martin
The embryonic development of vertebrates is characterized by controlled cell movements. During gastrulation and neurulation cells of the presumptive heart tissue and the neural crest after neural tube closure migrate towards their final position in the embryo. Cell intercalations, which drive the convergent extension (CE) movements to elongate the embryo also depend on active cell migration. The inhibition of CE leads to shortened body axis and neural tube closure defects (NTD). The motility of eukaryotic cells is finally based on the dynamic interaction of cytoskeletal components, which act on the actin filament. Secreted growthfactors of the Wnt family can regulate embryonic cell movement via the non canonical Wnt signaling pathways. The planar cell polarity (PCP) and the Wnt/Ca2+ pathway are thought to be crucial for the process of CE. Up to now there is a lack of knowledge about the cytoskeletal effectors of these signaling cascades. In the presented work, members of the calponin gene family (clp1 to 3) were analysed in this context. Calponins are actin binding proteins, which have been shown to inhibit actin-myosin-interactions and/or to stabilize the actin filament. Expression patterns provided first insights in the transcriptional activity of Xclp1, Xclp2 and Xclp3 during embryonic development. Two Xclp genes (Xclp2 and Xclp3) were already expressed broadly at the onset of gastrulation. Transcription, however, was not detected in the involuted cells, which form the mesodermal germlayer. At neurula stages Xclp2 mRNA was specifically found in the notochord, whereas Xclp3 was expressed in the neuroectoderm. Additionally the migrating cells of the embryonic heart and neural crest were positive for calponin expression. In summary the embryonic calponin pattern correlated with tissues in which cell movements occur. Over- or misexpression experiments were performed to manipulate embryonic calponin function in Xenopus laevis. Gain of function experiments however did not interfere with embryonic development. Probably calponin function was posttranslational negatively regulated in these experiments.The overexpression of calponin proteins, in which specific phosphorylation sites were mutated or known regulatory calponin domains deleted, again didn´t result in altered phenotypes. However, the misexpression of calponin actin binding domaine 2 (ABD2) inhibited the migration of Krox 20 positive neural crest cells, suggesting that in this tissue the Xclp ABD2 acts dominant negative. The presented data are not able to proof or disproof the hypothesis, that calponin proteins are effectors of the non canonical Wnt pathways.