OLSSON, Lennart; ERICSSON, Rolf; Friedrich-Schiller-Universit�t Jena; Uppsala University: Three-dimensional morphogenesis of cranial musculature in lungfishes and amphibians

Vertebrate head development is a classical topic that has received renewed attention during the last decade. Most reports use one of a few model organisms (chicken, mouse, zebrafish), and have focused on molecular mechanisms and the role of the neural crest, while cranial muscle development has received less attention. We work on a comparative project in which the goal is to describe the order of acquisition of innovations in selected phases of amphibian evolution. Both skull and cranial muscle development are in focus. We will present selected parts of this ongoing project including; cranial muscle differentiation and morphogenesis in the Australian lungfish and in Mexican axolotl, cranial muscle development in Xenopus laevis and the specialised relative Hymenochirus boettgeri , as well as skull development and morphology in a caecilian, Ichthyophis kohtaoensis , a burrowing animal where the head is used as a locomotory organ. To determine the onset of differentiation we use antibodies against desmin and optical sectioning using confocal laser scanning microscopy on whole-mount immunostained embryos. Antibodies against acetylated tubulin are used to clarify muscle innervation patterns. This technique makes it possible to document cranial muscle development in three dimensions while keeping the specimens intact. To obtain an appreciation of complicated three-dimensional structures in the head, we use reconstructions based on serial sections (two different methods will be shown). The project provides a morphological foundation for further studies of head skeleton as well as cranial muscle cell fate and early differentiation in a comparative approach. The focus is on understanding the developmental origins of morphological innovations.