Erin Strachan

Sox11 Is Required to Maintain Proper Levels of Hedgehog Signaling during Vertebrate Ocular Morphogenesis

Ocular coloboma is a sight-threatening malformation caused by failure of the choroid fissure to close during morphogenesis of the eye, and is frequently associated with additional anomalies, including microphthalmia and cataracts. Although Hedgehog signaling is known to play a critical role in choroid fissure closure, genetic regulation of this pathway remains poorly understood. Here, we show that the transcription factor Sox11 is required to maintain specific levels of Hedgehog signaling during ocular development. Sox11-deficient zebrafish embryos displayed delayed and abnormal lens formation, coloboma, and a specific reduction in rod photoreceptors, all of which could be rescued by treatment with the Hedgehog pathway inhibitor cyclopamine. We further demonstrate that the elevated Hedgehog signaling in Sox11-deficient zebrafish was caused by a large increase in shha transcription; indeed, suppressing Shha expression rescued the ocular phenotypes of sox11 morphants. Conversely, over-expression of sox11 induced cyclopia, a phenotype consistent with reduced levels of Sonic hedgehog. We screened DNA samples from 79 patients with microphthalmia, anophthalmia, or coloboma (MAC) and identified two novel heterozygous SOX11 variants in individuals with coloboma. In contrast to wild type human SOX11 mRNA, mRNA containing either variant failed to rescue the lens and coloboma phenotypes of Sox11-deficient zebrafish, and both exhibited significantly reduced transactivation ability in a luciferase reporter assay. Moreover, decreased gene dosage from a segmental deletion encompassing the SOX11 locus resulted in microphthalmia and related ocular phenotypes. Therefore, our study reveals a novel role for Sox11 in controlling Hedgehog signaling, and suggests that SOX11 variants contribute to pediatric eye disorders.

A secreted WNT-ligand-binding domain of FZD5 generated by a frameshift mutation causes autosomal dominant coloboma

Ocular coloboma is a common eye malformation resulting from incomplete fusion of the optic fissure during development. Coloboma is often associated with microphthalmia and/or contralateral anophthalmia. Coloboma shows extensive locus heterogeneity associated with causative mutations identified in genes encoding developmental transcription factors or components of signaling pathways. We report an ultra-rare, heterozygous frameshift mutation in FZD5 (p.Ala219Glufs*49) that was identified independently in two branches of a large family with autosomal dominant non-syndromic coloboma. FZD5 has a single-coding exon and consequently a transcript with this frameshift variant is not a canonical substrate for nonsense-mediated decay. FZD5 encodes a transmembrane receptor with a conserved extracellular cysteine rich domain for ligand binding. The frameshift mutation results in the production of a truncated protein, which retains the Wingless-type MMTV integration site family member-ligand-binding domain, but lacks the transmembrane domain. The truncated protein was secreted from cells, and behaved as a dominant-negative FZD5 receptor, antagonizing both canonical and non-canonical WNT signaling. Expression of the resultant mutant protein caused coloboma and microphthalmia in zebrafish, and disruption of the apical junction of the retinal neural epithelium in mouse, mimicking the phenotype of Fz5/Fz8 compound conditional knockout mutants. Our studies have revealed a conserved role of Wnt-Frizzled (FZD) signaling in ocular development and directly implicate WNT-FZD signaling both in normal closure of the human optic fissure and pathogenesis of coloboma.

Identification of Clonotypic IgH VDJ Sequences in Multiple Myeloma

In multiple myeloma (MM) the rearranged immunoglobulin heavy chain (IgH) variable, diversity, and joining (VDJ) DNA sequence of malignant plasma cells (PCs) serves as a marker for cells in the MM clone. This clonotypic sequence can be isolated from MM PCs by reverse transcriptase polymerase chain reaction (RT-PCR) with consensus primers that amplify the rearranged IgH repertoire. This chapter focuses on the key steps in determining patient-specific clonotypic sequences, including bulk RT-PCR using purified bone marrow mononuclear cell (BMMC) RNA, single-cell RT-PCR using RNA from PCs sorted by flow cytometry, IgH sequence alignments using IMGT or V BASE, and patient-specific primer design. In a test panel of several MM patient BMMCs, primers specific for the proposed sequence must amplify IgH from only the original patient. Furthermore, the proposed IgH sequence is not confirmed as clonotypic until these primers generate positive amplifications in the majority of single PCs from the original patient. This two-part test ensures that the proposed IgH sequence satisfies the definition of the clonotypic sequence as the most frequent, unique IgH sequence in an MM patient PC sample. With this patient-specific MM marker, a better understanding of transformed PCs and their B-lineage predecessors can be developed.

Genetic background-dependent role of Egr1 for eyelid development.

Significance Eyelid formation begins at approximately day E15.5 in mice. Over the next 24 h, the epidermis of both upper and lower eyelids rapidly grows and merges to cover the cornea. Here, we demonstrate that Egr1−/− mice on the C57BL/6 background have normal eyelid development, but back-crossing to BALB/c background for four or five generations resulted in defective eyelid development by embryonic day E15.5. This defective eyelid formation was then further associated with profound ocular anomalies evident by postnatal days 1-4. The BALB/c albino phenotype associated with the Tyrc tyrosinase mutation also appeared to contribute to the phenotype. Thus EGR1 in a genetic background-dependent manner plays a critical role in mammalian eyelid development, with subsequent impact on ocular integrity. EGR1 is an early growth response zinc finger transcription factor with broad actions, including in differentiation, mitogenesis, tumor suppression, and neuronal plasticity. Here we demonstrate that Egr1−/− mice on the C57BL/6 background have normal eyelid development, but back-crossing to BALB/c background for four or five generations resulted in defective eyelid development by day E15.5, at which time EGR1 was expressed in eyelids of WT mice. Defective eyelid formation correlated with profound ocular anomalies evident by postnatal days 1–4, including severe cryptophthalmos, microphthalmia or anophthalmia, retinal dysplasia, keratitis, corneal neovascularization, cataracts, and calcification. The BALB/c albino phenotype-associated Tyrc tyrosinase mutation appeared to contribute to the phenotype, because crossing the independent Tyrc-2J allele to Egr1−/− C57BL/6 mice also produced ocular abnormalities, albeit less severe than those in Egr1−/− BALB/c mice. Thus EGR1, in a genetic background-dependent manner, plays a critical role in mammalian eyelid development and closure, with subsequent impact on ocular integrity.