The Extracellular Matrix of Multi-Cellular Animals

• *Describe the 3 main types of cells and the 3 main types of fibers found in connective tissue? Reference Table 5.6.

55) Which of the following substances would NOT be found in significant amounts in the extracellular matrix of the illustrated areolar connective tissue? Keratin

Thinner, more darkly stained elastic fibers composed of the protein elastin can also be seen. The principal type of cells seen are lightly-staining fibroblasts that secrete the matrix materials.

In this report i will be writing brief description on the functions of the main cell components of the body cell.

Epithelial-mesenchymal transition (EMT) is a cellular process that is essential for normal processes in many organisms, including embryonic development and wound healing, and is recapitulated in human disease, contributing to organ fibrosis and cancer progression (Thiery et al. 2009; Yang and Weinberg 2008). EMT describes the conversion of a cell with an epithelial phenotype to one with mesenchymal characteristics and can be a partial or complete transformation. Epithelial cells form the borders of tissues and organs, and are characterized by apical-basal polarity, contact with a basement membrane, and strong adherence to other epithelial cells through intercellular junctions including adherens junctions, tight junctions, and desmosomes. Conversely, mesenchymal cells have front-rear polarity and generally lack cell-cell contact, allowing them to be motile. During human embryonic development, EMT is essential for the formation of a variety of tissues, including mesoderm, neural crest, somites, palate, pancreas, liver, reproductive tracts, and heart valves (Thiery et al. 2009; Yang and Weinberg 2008). After development, partial EMT also contributes to wound healing (Thiery et al. 2009). However, EMT can also play a more insidious role by factoring into tumour progression.

The second type of tissue found in the body is connective tissue. They lie beneath the epithelial tissue helping to connect different part of the internal structure, the cells are more widely separated from each other then in epithelial tissue. The intercellular substance known as the matrix is found in considerably large amounts. Within the matrix there are usually fibres which may be a jelly like consistency or dense and rigid depending on the type, function and positioning of the tissue. Theses fibres form a supporting system for cells to attach to. The major functions of connective tissue are to transport materials, give structural support and protection. The types of connective tissue that will be explained are blood, bone, cartilage, bone, areolar tissue and adipose tissue.

The next two molecules, α6β4 integrin, and collagen XVII extend beyond the basal keratinocyte membrane and into the lamina lucida layer of the basement membrane zone and hence they are known as transmembrane molecules. These latter two molecules can be found within the outer plaque of the hemidesmosome. The last molecule, CD151, the most recently discovered molecule, is closely associated with α6β4 Integrin, and resides at or near the surface of the basal cell plasma membrane. The intermediate filaments attach to BPAG1 and plectin, which compose the hemidesmosome inner plaque. Both plectin and BPAG1 belong to the plakin family of proteins, and share significant sequence homology.[14]

When TGase was knocked down, the HPT cells stared to migrate out of the tissue. The effect of extracellular of TGase activity was decreased in HPT culture with crude astakine supplementation (8). This studies strongly suggest that TGase activity is important for extracellular matrix (ECM) stabilization and decrease of its extracellular activity is mediated the hemocyte releasing from HPT. However, the role of astakine1 in TGase regulation still unclear. In crayfish, in addition to collagen IV (9), HPT tissue contains an abundant of clotting protein (unpublished data), which known as noncollagenous TGase substrate. This suggested that collagen and/or clotting may be involved in HPT cell renewal. In osteoblast, TGase activity has been reported to be an essential for an initial formation of a fibronectin-collagen network which subsequent affects to cell differentiation and mineralization of the cultures (10). In addition, 5-HT, a monoamine with a variety of physiological function as well as regulation of bone mass, has been determined to be an inhibitor of FXIIIa. 5-HT treatment resulted in directly inhibit FXIIIa mediate crosslinking of plasma fibronectin and leads to decreasing the stabilization of extracellular matrix networks (11).

CD 36 is a type of integrin protein, which is found mostly in the human. It usually binds to collagen, thrombospondin, anionic phospholipids and more. They are also glycosylated, and are an integrin plasma membrane protein that vary in a family that bind to lipid receptors. It functions in recognizing different lipoproteins, fatty acid transports, and cell – matrix interactions. This integrin is very diverse and deals mostly with fatty acid structures.

Cancer metastasis in the main character and hallmark of cancer progression [6]. Metastasis is a multi-step process beginning from detachments of cancer cells from the primary tumor, disruption of the basement membrane for invading to surrounding tissue. Subsequently, the cancer cells able entry to the blood and lymphatic system to spread into other part of the body and extravasation for growth and proliferate in distant sites [7]. Matrix metalloproteinase (MMP) is a zinc-dependent endopeptidase which responsible in degradation the component of extracellular matrix (ECM) proteins including collagen, elastin, fibronectin. MMP can secrete by inflammatory cells, osteoblast, fibroblast, and also cancer cells. MMP has a pivotal role in promoting

About one quarter of all the protein in your body is collagen. It is a major structural material that forms molecular cables to strengthen the tendons and resilient sheets that support the skin and internal organs. Bones and teeth are made by adding mineral crystals to collagen. Collagen provides structure to our bodies, protecting and supporting the softer tissues and connecting them with the skeleton. But, in spite of its critical function in the body, collagen is a relatively simple protein.

Among other functions, TIMPs inhibit MMPs by preventing their activa- tion in the presence of soluble collagen ( 16 ). There is a deli- cate balance between MMPs and TIMPs regulating both the production and degradation of collagen in extracellular matrix. This balance is disrupted in hypertensive heart dis- ease. Of these enzymes, one called TIMP-1 appears to play a more significant role in this regulation in the human heart.

The importance of cellular adhesion in homotypic cell-cell contact is vital in the construction of basic tissues into differentiated organs and body systems (Pokutta, Drees, Yamada, Nelson & Weis, 2008). In the adhesion complex responsible for adherence, like cells are attracted to like cells during specialization, creating the separation of organ systems such as the tissue of skin from the tissue of the lung. When homologous cells are in proximity to one another, they form tight adhesion junctions that strengthen over time, commonly recognized as adherens junctions. These flexible, but stable junctions have specific chemical and molecular components that enable cells to adhere to each other and remain attached during development to retain integrity (Maiden & Hardin, 2011).

These barrier-forming cells are called "endothelial cells". You can think of "endothelial" as a synonym for "lining" or even just "barrier".

Epithelial cells are responsible for separating the human body from outside environment by forming a barrier usually line of ducts and organs. In two dimensional culture, epithelial cells form an intact cobblestone monolayer with high transepithelial electrical resistance. In three dimensional matrices such as collagen or matrigel, epithelial cells have a distinct cell polarity. The basal side of the epithelial cell attaches to the extracellular matrix through the basement membrane, and the apical side faces the lumen of the duct where it can secrete molecules into the lumen and control molecule uptake. This polarity is essential for the survival of the epithelial cell as detachment of the extracellular matrix leads to anoikis. Anoikis is programmed cell death upon the detachment from an extracellular matrix {Frisch, 1994 #115}. Epithelial cells form barriers through the interaction of specific epithelial proteins such as epithelial-cadherin (E-cadherin), claudins, occludins, and demsogleins {Baum, 2011 #5348;Turksen, 2011 #5346}. E-cadherin’s extracellular domain forms a homophilic interaction with other E-cadherin molecules of adjacent cells, forming adherens junctions. The cytosolic domain of E-cadherin is important for cortical actin assembly and the sequestration of β-catenin {Qin, 2005 #2184;Tian, 2011 #5344}. Claudins and occludins contribute to cell polarity by forming tight junctions which restrict integral membrane protein movement to