Differentially expressed genes in the lens of mimecan-null mice

Members of the small leucine-rich proteoglycans (SLRP) gene family are essential for normal collagen fibrillogenesis in various connective tissues and important regulators of cellular growth, differentiation, and tissue repair. Mimecan is a member of this gene family and is expressed in many connective tissues. We have previously reported that knockout of the mouse mimecan gene results in abnormal collagen fibrillogenesis, mainly in the cornea and skin. During the course of our studies on biological roles of mimecan in the eye, we found that this gene is expressed in the mouse lens. Here, we sought to identify gene expression changes in the lens that are associated with the absence of mimecan.

Reverse transcription-polymerase chain reaction amplification (RT-PCR), in situ hybridization (ISH), and immunohistochemistry (IHC) were used to determine mimecan expression in human and mouse eyes. Microarray hybridization was used to determine gene expression differences between lenses isolated from mimecan-null and wild type mice. Relative quantitative RT-PCR was used to verify the expression levels of a subset of the identified genes.

By ISH and IHC, mimecan mRNA was detected in cornea and lens at embryonic day 16.5 (E16.5) and postnatal day 10 (P10) mouse eyes. By RT-PCR, mimecan mRNA was detected in human cornea, lens, iris, and retina. In mimecan-null mice lenses, microarray analysis of 5,002 mouse genes demonstrated a more than two fold increase in expression of 65 genes and a more than two fold decrease in expression of 76 genes. Among genes with increased expression were cell adhesion molecules, G-protein coupled receptors, intracellular signaling molecules, genes involved in protein biosynthesis and degradation, and genes involved in immune function. Decreased expression was found in extracellular matrix molecules, calcium binding and transporting proteins, and genes known for their roles in regulating cellular motility. Intriguingly, decreased gene expression was observed with two SLRP family members, biglycan and condroadherin, as well as with several stress-response proteins, including gammaA-crystallin, hemoglobin alpha 1, and metallothionein 1. Quantitative RT-PCR confirmed changes in expression of 12 genes selected from the arrays.

In this report we present the first demonstration that mimecan is constitutively expressed in the vertebrate lens. The results from gene expression profiling reveal the ability of mimecan to influence expression of biglycan and chondroadherin, thereby indicating possible novel regulatory interactions between these SLRP family members. As with mimecan, the expression of chondroadrein in vertebrate lens has not been reported previously. Our results provide insight into the function of mimecan in the lens and enable further characterization of molecular mechanisms by which this protein exerts its biological roles.