Mutations in Lama1 Disrupt Retinal Vascular Development and Inner Limiting Membrane Formation

Abstract

The Neuromutagenesis Facility at the Jackson Laboratory generated a mouse model of retinal vasculopathy, nmf223, which is characterized clinically by vitreal fibroplasia and vessel tortuosity. nmf223 homozygotes also have reduced electroretinogram responses, which are coupled histologically with a thinning of the inner nuclear layer. The nmf223 locus was mapped to chromosome 17, and a missense mutation was identified in Lama1 that leads to the substitution of cysteine for a tyrosine at amino acid 265 of laminin ␣1, a basement membrane protein.Despite normal localization of laminin ␣1 and other components of the inner limiting membrane, a reduced integrity of this structure was suggested by ectopic cells and blood vessels within the vitreous. Immunohistochemical characterization of nmf223 homozygous retinas demonstrated the abnormal migration of retinal astrocytes into the vitreous along with the persistence of hyaloid vasculature. The Y265C mutation significantly reduced laminin N-terminal domain (LN) interactions in a bacterial twohybrid system. Therefore, this mutation could affect interactions between laminin ␣1 and other laminin chains. To expand upon these findings, a Lama1 null mutant, Lama1 tm1.1Olf , was generated that exhibits a similar but more severe retinal phenotype than that seen in nmf223 homozygotes. The increased severity of the Lama1 null mutant phenotype is probably due to the complete loss of the inner limiting membrane in these mice. This first report of viable Lama1 mouse mutants emphasizes the importance of this gene in retinal development. The data presented herein suggest that hypomorphic mutations in human LAMA1 could lead to retinal disease.

Laminins containing the β2 and γ3 chains regulate astrocyte migration and angiogenesis in the retina

“…Similarly, mutations in α-dystroglycan (a laminin receptor) and in an enzyme that participates in glycosylation of α-dystroglycan (POMGnT1) also produce defective deposition of laminin at the ILM, resulting in defective ILM formation Takahashi et al, 2011). In addition to ILM disruption, laminin, dystroglycan and POMGnT1 mutants also display abnormal astrocyte distribution and blood vessel formation (Edwards et al, 2010;Lee et al, 2005;Takahashi et al, 2011). These studies demonstrate that an intact ILM is necessary for normal astrocyte distribution in the retina.…”

“…In the retina, laminins are crucial for ILM formation (Pinzón-Duarte et al, 2010;Hirrlinger et al, 2011;Halfter et al, 2005;Edwards et al, 2010). Similarly, mutations in α-dystroglycan (a laminin receptor) and in an enzyme that participates in glycosylation of α-dystroglycan (POMGnT1) also produce defective deposition of laminin at the ILM, resulting in defective ILM formation Takahashi et al, 2011).…”

“…Moreover, deletion of laminin genes disrupts the formation of the retinal inner limiting membrane (ILM) (Pinzón-Duarte et al, 2010;Edwards et al, 2010). As laminins and their receptors regulate cell migration (Suh and Han, 2010;Fujiwara et al, 2004;Desban et al, 2006;Echtermeyer et al, 1996), including brain astrocytes in vitro (Armstrong et al, 1990), we hypothesize that laminins regulate both astrocyte migration and spatial organization in the retina.…”

Basement Membranes: Cell Scaffoldings and Signaling Platforms

“…The dy2J dystrophic mouse, possessing an in-frame deletion within the laminin a2LN domain, is characterized by attenuated muscle sarcolemmal and Schwann cell endoneurial basement membranes, muscle degeneration/regeneration and peripheral nerve amyelination (Sunada et al 1995a;. Missense-mutations of the a2 and a1 LN domains have been found to cause a mild neuromuscular and retinal defects respectively, the latter associated with a partial reduction in the ability of the LN domain to bind to its bLN and gLN partners (Patton et al 2008;Edwards et al 2010). Missense mutations clustered within the laminin b2LN domain are a cause of Pierson disease, a syndrome characterized by congenital nephrotic syndrome, ocular abnormalities, and neurologic deficits (Matejas et al 2010).…”

Role of laminins in physiological and pathological angiogenesis

“…3 panel II). These mice were blind and exhibited tortuous vessels with persistence of hyaloid vessels in the retina (Edwards et al, 2010). This observation points at a crucial role of the LM a1 chain in proper retinal blood vessel development.…”