Mutation in the mouse histone gene Hist2h3c1 leads to degeneration of the lens vesicle and severe microphthalmia.

During an ENU (N-ethyl-N-nitrosourea) mutagenesis screen, we observed a dominant small-eye mutant mouse with viable homozygotes. A corresponding mutant line was established and referred to as Aey69 (abnormality of the eye #69). Comprehensive phenotyping of the homozygous Aey69 mutants in the German Mouse Clinic revealed only a subset of statistically significant alterations between wild types and homozygous mutants. The mutation causes microphthalmia without a lens but with retinal hyperproliferation. Linkage was demonstrated to mouse chromosome 3 between the markers D3Mit188 and D3Mit11. Sequencing revealed a 358 A-> C mutation (Ile120Leu) in the Hist2h3c1 gene and a 71 T-> C (Val24Ala) mutation in the Gja8 gene. Detailed analysis of eye development in the homozygous mutant mice documented a perturbed lens development starting from the lens vesicle stage including decreasing expression of crystallins as well as of lens-specific transcription factors like PITX3 and FOXE3. In contrast, we observed an early expression of retinal progenitor cells characterized by several markers including BRN3 (retinal ganglion cells) and OTX2 (cone photoreceptors). The changes in the retina at the early embryonic stages of E11.5-E15.5 happen in parallel with apoptotic processes in the lens at the respective stages. The excessive retinal hyperproliferation is characterized by an increased level of Ki67. The hyperproliferation, however, does not disrupt the differentiation and appearance of the principal retinal cell types at postnatal stages, even if the overgrowing retina covers finally the entire bulbus of the eye. Morpholino-mediated knock-down of the hist2h3ca1 gene in zebrafish leads to a specific perturbation of lens development. When injected into zebrafish zygotes, only the mutant mouse mRNA leads to severe malformations, ranging from cyclopia to severe microphthalmia. The wild-type Hist2h3c1 mRNA can rescue the morpholino-induced defects corroborating its specific function in lens development. Based upon these data, it is concluded that the ocular function of the Hist2h3c1 gene (encoding a canonical H3.2 variant) is conserved throughout evolution. Moreover, the data highlight also the importance of Hist2h3c1 in the coordinated formation of lens and retina during eye development.

MAPK1 is required for establishing the pattern of cell proliferation and for cell survival during lens development.

The mitogen-activated protein kinases (MAPKs; also known as ERKs) are key intracellular signaling molecules that are ubiquitously expressed in tissues and were assumed to be functionally equivalent. Here, we use the mouse lens as a model system to investigate whether MAPK1 plays a specific role during development. MAPK3 is known to be dispensable for lens development. We demonstrate that, although MAPK1 is uniformly expressed in the lens epithelium, its deletion significantly reduces cell proliferation in the peripheral region, an area referred to as the lens germinative zone in which most active cell division occurs during normal lens development. By contrast, cell proliferation in the central region is minimally affected by MAPK1 deletion. Cell cycle regulators, including cyclin D1 and survivin, are downregulated in the germinative zone of the MAPK1-deficient lens. Interestingly, loss of MAPK1 subsequently induces upregulation of phosphorylated MAPK3 (pMAPK3) levels in the lens epithelium; however, this increase in pMAPK3 is not sufficient to restore cell proliferation in the germinative zone. Additionally, MAPK1 plays an essential role in epithelial cell survival but is dispensable for fiber cell differentiation during lens development. Our data indicate that MAPK1/3 control cell proliferation in the lens epithelium in a spatially defined manner; MAPK1 plays a unique role in establishing the highly mitotic zone in the peripheral region, whereas the two MAPKs share a redundant role in controlling cell proliferation in the central region of the lens epithelium.

Early morphogenesis of persistent hyperplastic tunica vasculosa lentis and primary vitreous. A transmission electron microscopic study.

This report provides transmission electron microscopic observations on the early pathogenesis of persistent hyperplastic tunica vasculosa lentis/persistent hyperplastic primary vitreous (PHTVL/PHPV) in affected canine fetuses at days 28-44 postcoitum. The retrolental tissue by which this anomaly is characterized consists of loosely arranged fibroblasts in a randomly oriented meshwork of collagenous fibrils. Some of these cells contain melanosomes at day 44. In one day-44 eye, cells of neuroectodermal origin (Müller cells; fibrous astrocytes) were observed. From day 37 onward, the posterior subcapsular part of the lens contains rounded, increased intercellular spaces, resembling vacuoles, which deform the shape of the lens fibers. The posterior lens capsule develops normally until day 30. From day 35 onward the capsule has an amorphous ultrastructure, as opposed to the clearly laminated ultrastructure in reference eyes at day 35. In addition, the capsule's thickness increases until day 35, and, instead of growing thicker, decreases thereafter. Based on these results, it is hypothesized that a primary metabolic disorder in the lens fibers, subsequently leading to the formation of an abnormal posterior lens capsule, constitutes the primary defect in the sequence of events leading to PHTVL/PHPV.