Roles of zebrafish Nipped-B-like (Nipbl) in gene regulation

Abstracts / Developmental Biology 331 (2009) 431–441 Prep1 (Pknox1) is a homeodomain transcription factor in theTALE superfamily and a critical regulator of hematopoiesis and organogenesis. Although Prep1 null mice die at gastrulation, we found that a genetic combination of a Prep1 null allele with a hypomorphic allele (Prep1 i/− ) rescues embryonic viability until mid-gestation allowing new insights into its function in early development. Severe Prep1 i/− embryos show complex and dramatic anterior phenotypes, including anophthalmia or micro- phthalmia. The primary ocular phenotype appears to be complete absence of the lens, and analyses of lens development revealed that lens induction failed in Prep1 i/− embryos, accompanied by decreased or absent Pax6 and Foxe3 expression. Prep1 was required for Pax6 ectodermal enhancer (EE) activity, but not pancreatic enhancer activity. Using protein-binding microarray analysis, we identified two tandem highly conserved Prep1 bindings sites in the Pax6 EE, predicted to be of medium-affinity binding strength. These affinity differences were verified using biophysical real- time measurements of protein/DNA interactions. Mutation of either site abrogated Pax6 EE reporter activity, which could be rescued by mutagen- esis of one of the sites to a high-affinity Prep1 binding site. Therefore, Prep1 is a novel regulator of lens induction and a newly identified and critical upstream regulator of Pax6. Moreover, we define a novel cis-regulatory logic, whereby medium-affinity transcription factor binding sites act additively to define a genetic threshold for gene activation. doi:10.1016/j.ydbio.2009.05.199 Program/Abstract # 178 Roles of zebrafish Nipped-B-like (Nipbl) in gene regulation Akihiko Muto a , Anne L. Calof b , Thomas F. Schilling a , Arthur D. Lander a a Dev and Cell Biol., Univ. of California, Irvine, CA, USA b Anatomy and Neurobiol., Univ. of California, Irvine, CA, USA Heterozygous loss of Nipped-B-like (NIPBL) is the most common cause of Cornelia de Lange Syndrome (CdLS). Nipbl has a highly conserved role in loading cohesin onto chromosomes, but studies in Drosophila suggest it also exerts genome-wide effects on gene expres- sion. Nipbl+/− mice display CdLS-like phenotypes, without chromo- some cohesion defects (unpublished data), suggesting that CdLS results from dysregulated gene regulation. To investigate how Nipbl affects gene expression, we disrupted Nipbl expression in zebrafish embryos. Zebrafish has two genes, zNipbl-1 and zNipbl-2, with >70% amino acid identity to mammalian Nipbl; both are expressed maternally and ubiquitously in early embryos. Knock-down of either zNipbl with antisense morpholinos (MOs) led to gross morphological defects by 12 hpf; effects were more severe when both genes were knocked down. To identify the earliest transcriptional changes due to loss of Nipbl function, microarray analyses were performed on morphants at gastrula stages (6.5–9.0 hpf). When both zNipbls were depleted with transla- tion-blocking MOs, at least 7 genes were significantly up-regulated by 6.5 hpf, just hours after the mid-blastula transition (MBT, onset of zygotic transcription). Maternal mRNAs for all 7 are found in embryos and normally degraded after MBT. Preliminary data suggest that it is not stabilization of maternal mRNAs, but inappropriate onset of zygotic transcription, that accounts for their up-regulation in zNipbl morphants. Experiments are underway to elucidate the effects of Nipbl on the transcription of these genes. Supported by the NIH P01-HD052860. doi:10.1016/j.ydbio.2009.05.200 Program/Abstract # 179 Imprinting analysis in the Acrodysplasia region of mouse chromosome 12 Erin McMurray, Eric D. Rogers, Jennifer V. Schmidt Department of Bio. Sci., University of Illinois at Chicago, Chicago, IL, USA The insertional mouse mutation Acrodysplasia (Adp) confers a parent- of-origin developmental phenotype, with animals inheriting the mutation from their father showing skeletal abnormalities, while those inheriting the mutation from their mother are normal. This parental-specific phenotype, along with mapping of the insertion to a region of chromosome 12 proposed to contain imprinted genes, suggested that disruption of genomic imprinting might underlie the Adp phenotype. Genomic imprinting is the process by which autosomal genes are epigenetically silenced on one of the two parental alleles; imprinting mutation phenotypes manifest after inheritance from one parent but not the other. Imprinted genes typically occur in dense clusters that contain few nonimprinted genes, and therefore assaying representative genes from the Adp critical region might identify any imprinted domains. Thirteen genes spaced across the Adp region were analyzed for imprinting, but all were found to be biallelically expressed. Other explanations must therefore be considered for the parent-of-origin Adp phenotype. doi:10.1016/j.ydbio.2009.05.201 Program/Abstract # 180 Molecular mechanism of wound-dependent Grh regulation Myungjin Kim, William McGinnis Department of Biology, UCSD, La Jolla, CA, USA Abstract #180 will be presented as scheduled, but will not be published due to lack of license agreement between authors and publisher. doi:10.1016/j.ydbio.2009.05.202 Program/Abstract # 181 Serine protease activation of epidermal wound response genes in Drosophila Rachel Patterson, Michelle T. Juarez, William J. McGinnis Division of Biology, The University of California San Diego, La Jolla, CA, USA Following epidermal damage, breaches in the skin or cuticle are repaired by the epidermal wound response, a survival mechanism that restores barrier integrity. However, the manner in which nearby unwounded epidermal cells sense the wound and begin the process of repair is unknown. Here we show that serine proteases and their inhibitors are involved in regulating the expression of wound response genes encoding Dopa decarboxylase (Ddc), a cuticular crosslinking enzyme and misshapen (msn), a kinase that activates JNK signaling that is crucial for epidermal tissue movement and fusion. Transgenic flies containing reporter constructs fused to upstream enhancer sequences of Ddc and msn were generated to monitor transcriptional expression after wounding. After simultaneous aseptic wounding and injection of the broad-spectrum serine protease trypsin into late stage embryos, widespread epidermal Ddc expression was observed. Similar wounding and injection of the serine protease inhibitor aprotinin resulted in highly reduced expression levels of msn surrounding the wound site. Aseptic wounding and injection of papain, a cysteine protease, seemed to have no effect on the normal wound response expression of msn, suggesting that the wound response is serine protease specific. Serine proteases have been found to play important wound healing roles in a variety of epithelial tissues. These enzymes also activate melanization events after septic wounding. Our results indicate that serine proteases can activate specific wound response genes following epidermal damage. doi:10.1016/j.ydbio.2009.05.203