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Fibronectin-like protein in Porifera: its role in cell aggregation
Abstract:
Experiments were carried out on a freshwater sponge (Ephydatia mulleri) in order to demonstrate the presence of fibronectin in Porifera. By using antibodies to highly purified human plasma fibronectin, the presence of a similar or identical protein could be demonstrated in the membranes of E. mulleri cells such as epithelial cells, fibroblast-like cells, and choanocytes. The reaction was specific, could be abolished by the addition of excess fibronectin, and was not observed with nonimmune rabbit serum. The immune fluorescent reaction became stronger when the sponge cells were pretreated with acetone and could also be observed, although with a less intense staining, on the intercellular matrix. This shows the predominant presence of a sponge fibronectin-like protein in the cell membranes and also its presence to a lesser extent in the intercellular matrix. When dissociated sponge cells were led to reassociate under the microscope, reassociation could be completely inhibited by anti-human fibronectin antiserum up to a dilution of 1:120 and partially inhibited up to a dilution of 1:240. The reassociation of dissociated sponge cells could also be inhibited by the addition of purified gelatin but not with serum albumin or with a normal, nonimmune rabbit serum. These results clearly indicate that a sponge cell fibronectin-like protein may play an important role as the (or one of the) recognition site(s) of the aggregation factor(s) and can therefore be directly involved in cell association, morphogenesis, and differentiation.
Insights
Researchers found a fibronectin-like protein in freshwater sponges (Ephydatia mulleri). This protein is crucial for cell membrane interactions and sponge cell reassociation, impacting morphogenesis and differentiation.
Area of Science:
- Cell Biology
- Developmental Biology
- Marine Biology
Background:
- Fibronectin is a key protein in vertebrate cell adhesion and tissue development.
- Its presence and function in invertebrates, particularly primitive multicellular organisms like sponges, remain largely unexplored.
Purpose of the Study:
- To investigate the presence and localization of fibronectin or fibronectin-like proteins in the freshwater sponge Ephydatia mulleri.
- To determine the role of this sponge fibronectin-like protein in cell-cell adhesion and reassociation.
Main Methods:
- Immunofluorescence microscopy using antibodies against human plasma fibronectin.
- Acetone fixation of sponge cells to enhance antibody binding.
- Inhibition assays using anti-fibronectin antiserum and purified proteins (gelatin, serum albumin) to study cell reassociation.
Main Results:
- A fibronectin-like protein was detected predominantly in the cell membranes of E. mulleri cells (epithelial cells, fibroblast-like cells, choanocytes) and to a lesser extent in the intercellular matrix.
- Anti-human fibronectin antiserum significantly inhibited the reassociation of dissociated sponge cells.
- Purified gelatin also inhibited cell reassociation, unlike serum albumin or nonimmune rabbit serum.
Conclusions:
- Ephydatia mulleri possesses a fibronectin-like protein, primarily located in cell membranes.
- This sponge fibronectin-like protein plays a significant role in cell-cell recognition and adhesion, potentially acting as a binding site for aggregation factors.
- The findings suggest this protein is involved in sponge cell association, morphogenesis, and differentiation, highlighting conserved functions of fibronectin-like molecules across species.