MECHANISMS OF ORGANOGENESIS
The mechanisms that regulate establishment of complex tissue structures of functional organs are based on cell-cell and tissue interactions. During these interactions the cells send and receive signals that set up and execute the yet poorly understood developmental programs. These circuits commit the cells to specific fates and instruct them to construct cellular assemblies via morphoregulation. One of the major challenges in the field is to reveal the details of these processes and how these have been changed during evolution.
We provided evidence that in the context of the mammalian kidney, the Wnt signaling pathway is critical to trigger the genomic program that leads to composition of the key functional unit of the kidney, the nephron. One of the major current tasks in our research line is to reveal the cellular and molecular details how the Wnt signal transduction induces and controls nephrogenesis. The nephron precursor cells with in a so-called CAP mesenchyme (MM), express transcription factors such as Six2, Cited1, TCF21/Pod1 and WT-I. When the MM undergoes mesenchyme to epithelium transition to assemble a renal vesicle extracellular matrix (ECM) in the MM undergoes major changes. For example Wnt induced changes occur in expression of collagens, laminins, fibronectin and proteoglycans and their integrin receptors. Also the cell adhesion molecules (CAMs/Cadherin’s) expression undergoes a shift.
The MM contains progenitors or stem cells of the nephrons. The maintenance of these cells appears to be some how regulated by an interplay between the Wnt, Notch, FGF and BMP signaling pathways and their antagonists. Once the MM starts to form the epithelial renal vesicle which is remodeled via the motor proteins including acting these events are in part directed by yet poorly described mechanical forces.
Once the renal vesicle has formed the subsequent nephrogenesis steps, segmentation of the epithelium involves so-called planar cell polarity pathway (PCP). The PCP function establishes a highly convoluted nephron tubular system that integrates around 40 different cell types essential for kidney function. Nephron development is connected to integration of the endothelial cells in glomerulogenesis. The guidance to the endothelial cells to intermingle with the podocytes is coordinated somehow by the hypoxia inducible factor (HIF) controlled activities. As a summary, to gain better understanding of the complexities of organogenesis several cellular processes and several factors systems biology need to be outlined and studied.
To obtain more throughput for the empirical studies we have developed several novel experimental in vivo and ex vivo cellular and molecular technologies. These should offer detailed experimental approaches to be conducted with in the kidney model system (Figure). Besides our Biocenter Oulu projects our aim in the InfoTech Oulu research program is set the ground for new openings to identify novel cell-cell interactions mechanisms. We will address roles of physical forces in the morphogenetic field by applying tools of microfluidistic, nanotechnology and magnetism in genome wide biosensor screens with robotics.
Figure. Illustration of some selected ex vivo technologies to address control kidney development.
a) The embryonic kidney that is micro surgically prepared from mouse embryo at E11.5 develops also ex vivo. b) The metanephric mesenchyme (MM, in blue) can be mechanically separated and recombined with the natural inducer tissue the ureteric bud and grown again as a reconstituted organ. c) Specific cells can also be purified with markers with FACS and magnetic beads for the studies. The MM can be induced with a Wnt signaling source to form nephron during the subculture or after being dissociated to single cells and reaggregated to allow detailed cellular and molecular manipulation of the nephron and stromal progenitor cells.
3. Future goals
Last updated: 28.1.2014