Mutations in Lama1 Disrupt Ganglion Cell Development and Axonal Migration in the Mouse

Abstract

Purpose: : Laminin α1, encoded by Lama1, is a key component in the inner limiting membrane (ILM) of the retina. Furthermore, the importance of laminin-111, which contains laminin α1, in neurite outgrowth is well known. Two mouse mutants bearing disruptions in Lama1 were used in this study to investigate the role of laminin α1 in ILM formation and ganglion cell development. One, Lama1^Δ, is a null animal created through Cre-lox technology and the other, Lama1^nmf223, bears a point mutation created through N-ethyl-N-nitrosourea-induced mutagenesis.

Methods: : The effects of two different Lama1 mutations on ILM formation were investigated using electron microscopy and immunohistochemistry. Retinal ganglion cell number and axonal patterning within the retina were investigated with immunohistochemistry.

Results: : In Lama1^Δ mutants, the ILM was completely absent leaving the nerve fiber layer exposed. The ILM of Lama1^nmf223 mice formed but with a reduced integrity as frequent breaks were observed. Ganglion cells, astrocytes, Müller cell endfeet, and blood vessels were observed in the vitreous of both mutants. Despite these ILM abnormalities, both mutants displayed normal neurofilament patterning within the central retina. Towards the periphery, however, the axons became tortuous. Interestingly, while these axonal abnormalities were observed at Pl in the Lama1^Δ mutants, they were not noted until 3 weeks of age in the Lama1^nmf223 mice and the phenotype was less severe. In addition, this tortuosity extended into the central retina of Lama1^Δ mice as early as P14 and was associated with a reduction in the number of neurofilaments. Labeling with anti-Brn3 demonstrated a decrease in ganglion cell number in Lama1^Δ mutants as early at P1. In Lama1^nmf223 mice, however, ganglion cell numbers were comparable to controls into adulthood with some mutants showing peripheral loss of these cells beginning at three months of age.

Conclusions: : Laminin α1 is necessary for normal formation of the ILM, the maintenance of the ganglion cell layer, and axonal migration within the retina.Abstract total 2046/2432 characters

Keywords: extracellular matrix • ganglion cells • retina: proximal (bipolar, amacrine, and ganglion cells)