Differentiation and angiogenic growth factor message in two mammalian lens epithelial cell lines

Lens epithelial cells in culture can sometimes be induced to form spheroid aggregates termed lentoid bodies, composed of cells exhibiting various characteristics of the more highly differentiated lens fiber cells. However, lentoid bodies are often slow to form, and the ability to produce them declines with serial subculture. It was therefore of interest to establish and/or characterize lens epithelial cell lines capable of forming lentoid bodies. The differentiation state was assessed in lentoid bodies formed by each of two lens epithelial cell lines, the transformed alpha TN4 cell line from mouse and the nontransformed N/N1135A cell line from rabbit. Lentoid and monolayer cultures of each cell line were examined for transcripts of the lens-specific alpha A-crystallin ("alpha A"), gamma D-crystallin ("gamma D"; formerly gamma 1-crystallin) and MP26 genes. alpha TN4 lentoid bodies contained 2.5 times the alpha A RNA found in monolayer cells, but lacked detectable gamma D and MP26 RNA. None of the three markers were detected in either lentoid or monolayer N/N1135A cultures grown under the conditions described. Lentoid body formation alone, therefore, does not indicate the extent of differentiation occurring. At least some of the changes in cell adhesion occurring during lentoid body formation involve laminin-like and fibronectin-like interactions, and are reminiscent of those observed during embryonic lens formation. Finally, vascular endothelial growth factor mRNA was absent from the lens but present in alpha TN4 cells, suggesting a mechanism whereby the lens tumors of the founder mouse became vascularized.