Search

The vertebrate eye anlage grows out of the brain and folds into bilayered optic cups. The eye is patterned along multiple axes, precisely controlled by genetic programs, to delineate neural retina, pigment epithelium, and optic stalk tissues. Pax genes encode developmental regulators of key morphogenetic events, with Pax2 being essential for interpreting inductive signals, including in the eye. PAX2 mutations cause ocular coloboma, when the ventral optic fissure fails to close. Previous studies established that Pax2 is necessary for fissure closure and to maintain the neural retina -- glial optic stalk boundary. Using a Pax2GFP/+ knock-in allele we discovered that the mutant optic nerve head (ONH) lacks molecular boundaries with the retina and RPE, rendering the ONH larger than normal. This was preceded by ventronasal cup mispatterning, a burst of overproliferation and followed by optic cup apoptosis. Our findings support the hypothesis that ONH cells are tripotential, requiring Pax2 to remain committed to glial fates. This work extends current models of ocular development, contributes to broader understanding of tissue boundary formation and informs the underlying mechanisms of human coloboma.

The human fovea is known for its distinctive pit‐like appearance, which results from the displacement of retinal layers superficial to the photoreceptors cells. The photoreceptors are found at high density within the foveal region but not the surrounding retina. Efforts to elucidate the mechanisms responsible for these unique features have ruled out cell death as an explanation for pit formation and changes in cell proliferation as the cause of increased photoreceptor density. These findings have led to speculation that mechanical forces acting within and on the retina during development underly the formation of foveal architecture. Here we review eye morphogenesis and retinal remodeling in human embryonic development. Our meta‐analysis of the literature suggests that fovea formation is a protracted process involving dynamic changes in ocular shape that start early and continue throughout most of human embryonic development. From these observations, we propose a new model for fovea development. [ABSTRACT FROM AUTHOR]

Previous in vitro studies demonstrated that Fringe glycosylation of the NOTCH1 extracellular domain at O -fucose residues in Epidermal Growth Factor-like Repeats (EGFs) 6 and 8 is a significant contributor to suppression of NOTCH1 activation by JAG1 or enhancement of NOTCH1 activation by DLL1, respectively. In this study, we sought to evaluate the significance of these glycosylation sites in a mammalian model by generating 2 C57BL/6J mouse lines carrying NOTCH1 point mutations, which eliminate O -fucosylation and Fringe activity at EGFs 6 (T232V) or 8 (T311V). We assessed changes to morphology during retinal angiogenesis, a process in which expression of Notch1 , Jag1 , Dll4 , Lfng , Mfng , and Rfng genes coordinate cell-fate decisions to grow vessel networks. In the EGF6 O -fucose mutant (6f/6f) retinas, we observed reduced vessel density and branching, suggesting that this mutant is a Notch1 hypermorph. This finding agrees with prior cell-based studies showing that the 6f mutation increased JAG1 activation of NOTCH1 during co-expression with inhibitory Fringes. Although we predicted that the EGF8 O -fucose mutant (8f/8f) would not complete embryonic development due to the direct involvement of the O -fucose in engaging ligand, the 8f/8f mice were viable and fertile. In the 8f/8f retina, we measured increased vessel density consistent with established Notch1 hypomorphs. Overall, our data support the importance of NOTCH1 O -fucose residues for pathway function and confirms that single O -glycan sites are rich in signaling instructions for mammalian development. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.10.043 Byline: Jiha Kim, James D. Lauderdale Keywords: Mouse; Zebrafish; Retina; Iris hypoplasia; Ectopic pupil; Aniridia; Small eye Abstract: The Pax6 transcription factor is required for multiple aspects of vertebrate eye development. The Pax6 gene encodes isoforms that either contain (Pax6+PD) or lack (Pax6[DELTA]PD) the N-terminal paired-box DNA-binding domain, in addition to the homeodomain. Alternative promoters control the expression of Pax6+PD and Pax6[DELTA]PD in the eye. Using a modified bacterial artificial chromosome (BAC) transgene that specifically expresses Pax6[DELTA]PD, but not paired-containing Pax6, in the normal endogenous pattern, we show that overexpression of Pax6[DELTA]PD causes a severe microphthalmic phenotype in both wild-type and Pax6-deficient (Sey.sup./+) mice in a dosage-dependent manner. The microphthalmic phenotype is due to lens degeneration during embryonic development. Lens development initiates correctly, but cells in the lens undergo apoptotic cell death between E12 and E13. Concomitantly, in these mice, changes in Bmp4, Msx1, and Wnt2b expression were observed in the mesenchymal cells of the developing cornea. To visualize Pax6[DELTA]PD expression, we developed a dual-reporter Pax6 BAC transgene in which EGFP and DsRed demonstrate paired-containing and pairedless transcripts, respectively. In BAC transgenic mice, DsRed is predominantly expressed in the peripheral neural retina during early eye development, but not in the developing lens or cornea. Later DsRed is strongly expressed in the developing ciliary body, but not in the iris. We suggest that the ratio of Pax6+PD and Pax6[DELTA]PD isoforms in the distal retina is important for both cornea and lens development, either directly by controlling transcription of necessary growth factors or indirectly by controlling development of the distal neural retina. Author Affiliation: Department of Cellular Biology, The University of Georgia, Athens, GA 30602, USA Article History: Received 9 November 2006; Revised 23 October 2007; Accepted 26 October 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.04.015 Byline: Jorn Lakowski, Anirban Majumder, James D. Lauderdale Keywords: Transgene; Alternative promoter; Retina; Eye Abstract: The Pax6 gene plays several roles in retinal development, including control of cell proliferation, maintenance of the retinogenic potential of progenitor cells, and cell fate specification. Emerging evidence suggests that these different aspects of Pax6 gene function are mediated by different isoforms of the Pax6 protein; however, relatively little is known about the spatiotemporal expression of Pax6 isoforms in the vertebrate retina. Using bacterial artificial chromosome (BAC) technology, we modified a zebrafish Pax6a BAC such that we could distinguish paired-containing Pax6a transcripts from paired-less Pax6a transcripts. In the zebrafish, the spatial and temporal onset of expression of these transcripts suggests that the paired-less isoform is involved in the cell fate decision leading to the generation of amacrine cells; however, because of limitations associated with transient transgenic analysis, it was not feasible to establish whether this promoter was active in all amacrine cells or in a specific population of amacrine cells. By making mice transgenic for the zebrafish Pax6a BAC reporter transgene, we were able to show that paired-containing and paired-less Pax6a transcripts were differentially expressed in amacrine subpopulations. Our study also directly demonstrates the functional conservation of the regulatory mechanisms governing Pax6 transcription in teleosts and mammals. Author Affiliation: Department of Cellular Biology, The University of Georgia, Athens, GA 30602, USA Article History: Received 21 September 2006; Revised 16 March 2007; Accepted 12 April 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2005.12.041 Byline: Jiha Kim, James D. Lauderdale Keywords: Pax6; BAC transgene; Olfactory bulb; Mitral cells; Eye; Long-distance transcriptional regulation; Migratory neurons; Mouse; Aniridia; Small eye Abstract: Pax6, a member of the paired-family of transcription factors, exhibits restricted expression and essential functions in the developing eye, olfactory system, central nervous system, and pancreas. To understand Pax6 function, which critically depends on induction of proper expression levels during development, it is necessary to elucidate the molecular mechanisms governing Pax6 transcription. Although previous studies using classic transgenic approaches have provided a wealth of information about the distribution and types of regulatory elements involved in Pax6 regulation, genetic studies in both humans and mice indicate that these enhancers alone are not sufficient for fully regulated Pax6 expression. We report here our analysis of mice transgenic for a 160 kb mouse Pax6 BAC transgene, which was generated as a necessary first step towards testing the long-range control of Pax6 expression in vivo. We show that this BAC transgene replicates Pax6 expression in the eye. This is the first time that a reporter transgene has been expressed in a normal Pax6-like pattern in all of the tissues of the eye and defines an eye regulatory region within the Pax6 downstream regulatory region (DRR). Second, we show that this BAC transgene contains all of the cis regulatory elements required for normal Pax6 expression within the developing embryo, except for within the diencephalon and olfactory bulb. Third, we show that this transgene is subject to Pax6 autoregulation. Lastly, we identify, for the first time in mammals, an isoform of the Pax6 protein lacking the paired domain. This isoform is expressed in the developing olfactory bulb and eye. Over-expression of Pax6[DELTA]PD causes a microphthalmic phenotype in both Pax6.sup.+/+ mice and Pax6.sup.+/- mice. These results demonstrate a role for Pax6[DELTA]PD in eye development, which appears to be different than that ascribed to either canonical Pax6 or Pax6(5a). Author Affiliation: Department of Cellular Biology, The University of Georgia, Athens, GA 30602, USA Article History: Received 2 June 2005; Revised 8 September 2005; Accepted 21 December 2005

The effects of plasmid length and positionednucleosomes on in vitro assembly of chromatins was investigated. The aim was tostudy the mechanism by which the well-ordered nucleosome spacing in chromatin is established. The study protocol involved systematically changing the plasmidlength by very small or very large amounts. The results showed that small plasmid size and strongly positioned nucleosomes affect the overall alignment induced by histone H5, and provides support for a quasicrystalline model of forthe generation of nucleosome arrays in chromatin.

Copyright of Laboratory Animals is the property of Sage Publications, Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)