Limits...
Mutations in zebrafish lrp2 result in adult-onset ocular pathogenesis that models myopia and other risk factors for glaucoma.

Veth KN, Willer JR, Collery RF, Gray MP, Willer GB, Wagner DS, Mullins MC, Udvadia AJ, Smith RS, John SW, Gregg RG, Link BA - PLoS Genet. (2011)

Bottom Line: Detailed phenotype analyses indicated that as lrp2 mutant fish age, many individuals--but not all--develop high IOP and severe myopia with obviously enlarged eye globes.This results in retinal stretch and prolonged stress to retinal ganglion cells, which ultimately show signs of pathogenesis.Our studies implicate altered Lrp2-mediated homeostasis as important for myopia and other risk factors for glaucoma in humans and establish a new genetic model for further study of phenotypes associated with this disease.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America.

ABSTRACT
The glaucomas comprise a genetically complex group of retinal neuropathies that typically occur late in life and are characterized by progressive pathology of the optic nerve head and degeneration of retinal ganglion cells. In addition to age and family history, other significant risk factors for glaucoma include elevated intraocular pressure (IOP) and myopia. The complexity of glaucoma has made it difficult to model in animals, but also challenging to identify responsible genes. We have used zebrafish to identify a genetically complex, recessive mutant that shows risk factors for glaucoma including adult onset severe myopia, elevated IOP, and progressive retinal ganglion cell pathology. Positional cloning and analysis of a non-complementing allele indicated that non-sense mutations in low density lipoprotein receptor-related protein 2 (lrp2) underlie the mutant phenotype. Lrp2, previously named Megalin, functions as an endocytic receptor for a wide-variety of bioactive molecules including Sonic hedgehog, bone morphogenic protein 4, retinol-binding protein, vitamin D-binding protein, and apolipoprotein E, among others. Detailed phenotype analyses indicated that as lrp2 mutant fish age, many individuals--but not all--develop high IOP and severe myopia with obviously enlarged eye globes. This results in retinal stretch and prolonged stress to retinal ganglion cells, which ultimately show signs of pathogenesis. Our studies implicate altered Lrp2-mediated homeostasis as important for myopia and other risk factors for glaucoma in humans and establish a new genetic model for further study of phenotypes associated with this disease.

Show MeSH

Related in: MedlinePlus

Adult bugeye zebrafish have enlarged eye globes, thinned retinas, and elevated intraocular pressure without iridocorneal angle obstruction or malformation.A,C Dorsal views of adult wild-type (A) and bugeye (C) zebrafish. B,D Histology of central retina sections at 6 months in wild-type (B) and mutant (D) eyes. E-H Histology of wild-type (E,F) and bugeye mutant (G,H) iridocorneal angles in the dorsal region (E,G) or at the ventral canalicular aqueous humor drainage region (F,H). I Intraocular pressures (IOP) in adult wild-type and bugeye zebrafish. IOPs in bugeye fish were elevated compared to age and size matched fish from TL wild-type stain (p<0.0001, t-test). Scale bars: A,C = 4 mm; B,D = 50 µm; E-H = 40 µm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3040661&req=5

pgen-1001310-g001: Adult bugeye zebrafish have enlarged eye globes, thinned retinas, and elevated intraocular pressure without iridocorneal angle obstruction or malformation.A,C Dorsal views of adult wild-type (A) and bugeye (C) zebrafish. B,D Histology of central retina sections at 6 months in wild-type (B) and mutant (D) eyes. E-H Histology of wild-type (E,F) and bugeye mutant (G,H) iridocorneal angles in the dorsal region (E,G) or at the ventral canalicular aqueous humor drainage region (F,H). I Intraocular pressures (IOP) in adult wild-type and bugeye zebrafish. IOPs in bugeye fish were elevated compared to age and size matched fish from TL wild-type stain (p<0.0001, t-test). Scale bars: A,C = 4 mm; B,D = 50 µm; E-H = 40 µm.

Mentions: The bugeye zebrafish mutant was identified in a three-generation forward-genetic screen for adult ocular abnormalities. Mutants were easily identified by 6 months as their eyes were visibly enlarged (Figure 1A, 1C). Interestingly, the degree of eye enlargement often varied between the two eyes of a single fish (Figure S1A–S1G). Occasionally the phenotype presented only in one eye, and the other eye remained normal in size (Figure S1B). To address whether ocular enlargement in mutants might represent a retinoblastoma phenotype, we analyzed eyes by histology. Instead of obvious cellular overgrowth we found that the retina was notably thinner in all layers (Figure 1B, 1D). As buphthalmia is often associated with elevated IOP, we used servo- electrophysiology to measure the eye pressures in mutants and wild-type siblings [14]. Compared to wild-type fish, bugeye mutants consistently showed elevated IOPs (Figure 1I). In addition, the rare fish that presented the phenotype in a unilateral manner had normal pressure in the wild-type sized eye and elevated pressure in the enlarged eye (Figure S1H). IOP is maintained by the balance of aqueous humor production and drainage. Like mammals, aqueous humor in zebrafish is produced in the ciliary epithelium and drained at the iridocorneal angle. However, unlike mammals where drainage occurs circumferentially throughout the angle region, aqueous outflow for zebrafish is facilitated through a discrete ventrally localized canalicular network [15]. Histology did not reveal obvious disorganization in either the dorsal ciliary epithelium (Figure 1E, 1G) or in the ventral canalicular outflow network (Figure 1F, 1H). However, the ciliary epithelium occasionally appeared mildly hypertrophied (Figure 1G, arrow) and the angle region of mutants was more prone than wild-type specimens to separation between the iris and corneal tissues during histological preparation (Figure 1H, asterisk). Additional characterization of these regions at the time of phenotype onset confirmed these observations (Figure S2).


Mutations in zebrafish lrp2 result in adult-onset ocular pathogenesis that models myopia and other risk factors for glaucoma.

Veth KN, Willer JR, Collery RF, Gray MP, Willer GB, Wagner DS, Mullins MC, Udvadia AJ, Smith RS, John SW, Gregg RG, Link BA - PLoS Genet. (2011)

Adult bugeye zebrafish have enlarged eye globes, thinned retinas, and elevated intraocular pressure without iridocorneal angle obstruction or malformation.A,C Dorsal views of adult wild-type (A) and bugeye (C) zebrafish. B,D Histology of central retina sections at 6 months in wild-type (B) and mutant (D) eyes. E-H Histology of wild-type (E,F) and bugeye mutant (G,H) iridocorneal angles in the dorsal region (E,G) or at the ventral canalicular aqueous humor drainage region (F,H). I Intraocular pressures (IOP) in adult wild-type and bugeye zebrafish. IOPs in bugeye fish were elevated compared to age and size matched fish from TL wild-type stain (p<0.0001, t-test). Scale bars: A,C = 4 mm; B,D = 50 µm; E-H = 40 µm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3040661&req=5

pgen-1001310-g001: Adult bugeye zebrafish have enlarged eye globes, thinned retinas, and elevated intraocular pressure without iridocorneal angle obstruction or malformation.A,C Dorsal views of adult wild-type (A) and bugeye (C) zebrafish. B,D Histology of central retina sections at 6 months in wild-type (B) and mutant (D) eyes. E-H Histology of wild-type (E,F) and bugeye mutant (G,H) iridocorneal angles in the dorsal region (E,G) or at the ventral canalicular aqueous humor drainage region (F,H). I Intraocular pressures (IOP) in adult wild-type and bugeye zebrafish. IOPs in bugeye fish were elevated compared to age and size matched fish from TL wild-type stain (p<0.0001, t-test). Scale bars: A,C = 4 mm; B,D = 50 µm; E-H = 40 µm.
Mentions: The bugeye zebrafish mutant was identified in a three-generation forward-genetic screen for adult ocular abnormalities. Mutants were easily identified by 6 months as their eyes were visibly enlarged (Figure 1A, 1C). Interestingly, the degree of eye enlargement often varied between the two eyes of a single fish (Figure S1A–S1G). Occasionally the phenotype presented only in one eye, and the other eye remained normal in size (Figure S1B). To address whether ocular enlargement in mutants might represent a retinoblastoma phenotype, we analyzed eyes by histology. Instead of obvious cellular overgrowth we found that the retina was notably thinner in all layers (Figure 1B, 1D). As buphthalmia is often associated with elevated IOP, we used servo- electrophysiology to measure the eye pressures in mutants and wild-type siblings [14]. Compared to wild-type fish, bugeye mutants consistently showed elevated IOPs (Figure 1I). In addition, the rare fish that presented the phenotype in a unilateral manner had normal pressure in the wild-type sized eye and elevated pressure in the enlarged eye (Figure S1H). IOP is maintained by the balance of aqueous humor production and drainage. Like mammals, aqueous humor in zebrafish is produced in the ciliary epithelium and drained at the iridocorneal angle. However, unlike mammals where drainage occurs circumferentially throughout the angle region, aqueous outflow for zebrafish is facilitated through a discrete ventrally localized canalicular network [15]. Histology did not reveal obvious disorganization in either the dorsal ciliary epithelium (Figure 1E, 1G) or in the ventral canalicular outflow network (Figure 1F, 1H). However, the ciliary epithelium occasionally appeared mildly hypertrophied (Figure 1G, arrow) and the angle region of mutants was more prone than wild-type specimens to separation between the iris and corneal tissues during histological preparation (Figure 1H, asterisk). Additional characterization of these regions at the time of phenotype onset confirmed these observations (Figure S2).

Bottom Line: Detailed phenotype analyses indicated that as lrp2 mutant fish age, many individuals--but not all--develop high IOP and severe myopia with obviously enlarged eye globes.This results in retinal stretch and prolonged stress to retinal ganglion cells, which ultimately show signs of pathogenesis.Our studies implicate altered Lrp2-mediated homeostasis as important for myopia and other risk factors for glaucoma in humans and establish a new genetic model for further study of phenotypes associated with this disease.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America.

ABSTRACT
The glaucomas comprise a genetically complex group of retinal neuropathies that typically occur late in life and are characterized by progressive pathology of the optic nerve head and degeneration of retinal ganglion cells. In addition to age and family history, other significant risk factors for glaucoma include elevated intraocular pressure (IOP) and myopia. The complexity of glaucoma has made it difficult to model in animals, but also challenging to identify responsible genes. We have used zebrafish to identify a genetically complex, recessive mutant that shows risk factors for glaucoma including adult onset severe myopia, elevated IOP, and progressive retinal ganglion cell pathology. Positional cloning and analysis of a non-complementing allele indicated that non-sense mutations in low density lipoprotein receptor-related protein 2 (lrp2) underlie the mutant phenotype. Lrp2, previously named Megalin, functions as an endocytic receptor for a wide-variety of bioactive molecules including Sonic hedgehog, bone morphogenic protein 4, retinol-binding protein, vitamin D-binding protein, and apolipoprotein E, among others. Detailed phenotype analyses indicated that as lrp2 mutant fish age, many individuals--but not all--develop high IOP and severe myopia with obviously enlarged eye globes. This results in retinal stretch and prolonged stress to retinal ganglion cells, which ultimately show signs of pathogenesis. Our studies implicate altered Lrp2-mediated homeostasis as important for myopia and other risk factors for glaucoma in humans and establish a new genetic model for further study of phenotypes associated with this disease.

Show MeSH
Related in: MedlinePlus