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J. Zhang, S. Fuhrmann, M. L. Vetter; Selective Loss of Frizzled-5 Causes Persistent Hyperplastic Primary Vitreous (PHPV). Invest. Ophthalmol. Vis. Sci. 2008;49(13):3879.
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The Wnt receptor Frizzled-5 (Fzd5) is expressed in the developing mouse eye beginning at optic vesicle stages, suggesting a role during eye development. To assess this, we analyzed the effects of tissue-specific deletion of Fzd5, thus bypassing the early requirement for Fzd5 in embryonic viability.
We conditionally inactivated a LoxP-flanked Fzd5 allele in the mouse retina using Cre recombinase driven by the Six3 promoter. We crossed Fzd5+/- mice carrying the Six3-Cre transgene with Fzd5LoxP/LoxP mice to obtain Fzd5 conditional mutant embryos. Six3-Cre transgenic mice were crossed with ROSA-26 reporter mice to determine which cell lineages in the eye had Cre activity. Histological analysis was performed from embryonic day 14.5 (E14.5) to postnatal day 23 (P23) with hematoxylin and eosin staining on sections. Immunohistochemistry was used to analyze cell proliferation, vascularization and effects on retinal organization. Apoptosis was monitored by TUNEL staining.
With disruption of retinal Fzd5 expression we observed that the growth of the hyaloid and intravitreal vasculature was promoted as early as E14.5 and persisted into postnatal stages, appearing as a pigmented intravitreal mass. This ocular vasculature normally regresses gradually from E17.5 to P10 through apoptosis, however PCNA staining showed that in Fzd5 conditional knockout mice it continued to proliferate after birth even at P23. TUNEL staining revealed that apoptosis of the persistent vasculature was inhibited. Moreover, the morphogenesis of retina adjacent to the vasculature was disrupted leading to retinal folds, detachment, rosette structures and abnormal lamination. When the Six-Cre mice were crossed with the ROSA-26 reporter line lacZ activity was restricted to the retina, while the vasculature was negative, suggesting cell non-autonomous effects on retinal vasculature proliferation and regression.
The loss of Fzd5 signaling in the retina resulted in the failure of regression of the vitreous vasculature. This mouse provides a model of the human disease persistent hyperplastic primary vitreous (PHPV).
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