1. Morphogenesis Differentiation – 4 Cell-cell communication Lecture 12 BSE 652 23-2-2016

2. Maintenance of differentiated state

3. Laminin synthesizing Collagen synthesizing mesenchyme Extracellular matrices in the developing embryos  Collagens are the most abundant ECM molecules, in fact they constitute 25% of ALL proteins made in our body!  Proteoglycans play major role in delivery of paracrine factors  Fibronectin acts as a general adhesive molecule  Fibronectin interacts with migrating cells through specific molecules which aides in alignment of migrating cells to the ECM  Laminins are major components basal lamina, secreted by epithelial cells. The laminin-epithelial cell interaction is much stronger than fibronectin-mesenchyme interaction Fibronectin in the developing frog embryo. (A) Fluorescent antibodies to fibronectin show fibronectin deposition as a green band in the Xenopus embryo during gastrulation. The fibronectin will orient the mesoderm movements of the cells. Location and formation of extracellular matrices in the chick embryo. The scanning electron micrograph shows the extracellular matrix at the junction of the epithelial cells (above) and mesenchymal cells (below). The epithelial cells synthesize a tight, glycoprotein-based basal lamina, while the mesenchymal cells secrete a loose reticular lamina made primarily of collagen.

4. Integrins  Integrates ECM and cellular cytoskeleton.  ECM attachment seems to be a major survival signal Speculative diagram relating the binding of cytoskeleton to the extracellular matrix through the integrin molecule

5. ECM directed gene expression

6. Basement membrane-directed gene expression in mammary gland tissue. (A) Mouse mammary gland tissue divides when placed on tissue culture plastic. Cell division genes are on, and the genes capable of synthesizing the differentiated products of the mammary gland (lactoferrin, casein, whey acidic protein) are off. (B) When presented with basement membrane that contains laminin, the genes for cell division proteins are turned off, while the gene inhibiting cell division (p21) and the gene for lactoferrin are turned on. (C, D) Mammary gland cells wrap the basement membrane about them, forming a secretory epithelium. The genes for casein and whey protein are sequentially activated.

7. Epithelial mesenchymal transition Outline of EMT Formation of mesoderm – Mesenchymal cells delaminate from the epiblast