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Vertebrate Embryology

Research interest

Our group is interested in the developmental biology of higher vertebrates. We would like to understand how the vertebrate body is generated during embryogenesis. Starting off as a single cell, the embryo acquires progressively complex traits, including multiple cell types, multiple tissue types, and their species-specific arrangement in functional organs which cooperate to form the developing organism. We are investigating the cellular and molecular mechanisms regulating this fascinating process, including cell fate choice, cell migration, pattern formation and morphogenesis. Beyond embryogenesis we are searching for clues from developmental processes to understand the evolution of vertebrate anatomy.

Model systems and techniques

We mainly use the chicken embryo as a model system, as it allows us to combine classical techniques like microsurgery and immunohistochemistry with modern molecular approaches like local transfection of embryonic cells by in ovo electroporation and retroviral gene delivery, and visualization of the expression of developmentally relevant genes by in situ hybridization.

1. 2,5 days old chicken embryo in ovo (unpublished original)
2. 4 days old chicken embryo stained for muscle specific gene expression (MyoD) in the myotomes by in situ hybridization (unpublished original)
3. Muscle precursor cells emigrating from the somites into limb bud labelled by GFP electroporation, visualized by confocal microscopy (Scaal et al. 2004)

1. Three myotomes of a 5 days old chicken embryo labelled by GFP electroporation, visualized by confocal microscopy (unpublished original)
2. Quail-chicken-chimerization: After transplantation of a ventral somite half of a quail donor into a chicken host, donor cells (green) are found in sclerotomal anlagen of the vertebral column and in the wall of the dorsal aorta (red) (Wiegreffe et al. 2007)

Our research is presently focussed on the following topics:

Somite development

Somites are transient structures found in all chordate embryos. They form a series of mesodermal segments along the body axis, and give rise to a variety of mesodermal organs including the axial skeleton, skeletal muscle, connective tissue of the trunk, and blood vessels. We are studying the morphological dynamics and the molecular regulatory networks underlying the cell fate decisions within the somites, and the subsequent developmental steps leading to the differentiation of somite-derived cells into tissues and organs. On the molecular level, our work presently focuses on signalling networks including Wnt and FGF signalling.
In an ongoing study, we are investigating the role of Wnt signaling and cell shape changes in cell type specification and the regulation of epithelio-mesenchymal transition during somite development. This work is funded by the SFB592 (Signaling mechanisms in embryogenesis and organogenesis), Project A1 to M.S..

Sagittal semithin section of somites I to IV of a 1,5 days old chicken embryo (unpublished original)

Localization of cellular markers labelled by immunohistochemistry in transverse sections of chicken embryos, visualization by confocal microscopy. On the left, section through the whole embryo at the level of somite formation, o the right higher magnification of a section through an epithelial somite (unpublished originals)

Loss of epithelial morphology in somites after inhibition of canonical Wnt signaling: electroporation of a dominant-negative construct of Lef1 visualized by a GFP reporter construct (left) leads to disrupted expression of the dermomyotomal marker gene Pax3 (right) (Krück and Scaal 2012)

Limb development

During embryogenesis, the vertebrate limbs originate as local protrusions of the lateral mesoderm, the limb buds, which are successively sculpted into functional legs and arms with their characteristic anatomy. This process involves the generation and realization of a three-dimensional pattern, and the spatially and temporally specific differentiation of precursor cells into skeleton, muscle, and other tissues. Notably, the limbs consist of both autochthonous cells originating in the lateral mesoderm, like the skeleton and the connective tissue, and of cells immigrating from the somites, like skeletal muscle and endothelia. We are mainly interested in limb patterning, in the mechanisms of somite cell migration into the limbs, and the control of local differentiation events within the limb anlagen.
In an ongoing project, we are investigating the implication of acetyltransferases as co-factors of known signalling pathways, including Wnt signalling, in limb pattern formation and growth. This work is funded by the GRK1104 (From cells to organs: Molecular mechanisms of organogenesis) to M.S., in collaboration with the laboratory of Dr. Ekkehardt Lausch in the Division of Human Genetics at the University Children Hospital in Freiburg i.Br.

Expression of Pleiotrophin in wing (left) and leg (right) joint and tendon anlagen of a 7 days old chicken embryo (Mittapalli et al. 2009)

Ectodermal Wnt signaling inhibits chondrogenesis. On the right, normal limb skeleton of a 6 days old chicken embryo visualized by Alcian blue staining. On the right, severe reduction of skeletogenesis after overexpression of Wnt6 (Geetha-Loganathan et al. 2010)