Congress Abstracts - Society for Developmental Biology

Zac1 expression in the developing cortex and spinal cord is restricted to the dividing neural progenitors in the VZ and SZ. Zac1
overexpression, in cortex and spinal cord, elicits cell cycle exit and expulsion from the germinal zones. In the cortex this is
accompanied by upregulation of the CKI Cdkn1c, whereas in the spinal cord Cdkn1b expression is induced. The premature cessation
of proliferation is, however, not accompanied by precocious acquisition of differentiated neuronal characteristics. In vitro, we show
that, Zac1 directly binds to the promoter region of the Cdkn1c gene and forcefully induces its expression. Our results show that Zac1
is a key regulator of cell cycle exit in cycling neural progenitors through the induction of CKIs. Furthermore, this study reveals a
molecular pathway that specifically regulates cell cycle exit without affecting other aspects of differentiation indicating that these
processes are not inextricably linked.
Program/Abstract # 142
Transcription regulation of anterior hypothalamic development
Mahmud, Abdullah Al (University of Montreal, Canada); Michaud, Jacques (CHU Sainte Justine, Canada)
The paraventricular nucleus (PVN) of the anterior hypothalamus regulates several processes that are critical for survival, including the
regulation of energy balance and of blood pressure. SIM1 directs the terminal differentiation of at least five types of PVN neurons
identifiable by the production of OT, AVP, CRH, SS and TRH. Whereas Sim1-/- mice die shortly after birth, Sim1+/- mice survive but
develop hyperphagia and early-onset obesity. We have shown that Sim1 functions along a physiological pathway in the PVN for the
control of food intake. Sim1 thus regulates the development of the PVN as well as its function. The objective of this project is to
identify novel regulators of PVN development. We have identified a regulatory element that specifically directs expression in all cells
of the developing PVN. Using this element, we have generated transgenic mice that express gfp in these cells. We next collected the
domain expressing gfp at different developmental stages (E11.5, E12.5, E13.5, E14.5 and E16.5) as well as the immediate posterior
domain of the developing hypothalamus. We are currently comparing the transcriptomes from these samples by performing RNA-seq.
We have also used the same strategy to collect hypothalamic samples from Sim1 mutant and wild-type embryos. By comparing the
transcriptomes of these different sets of embryos, we will be in a position to identify the factors that are directly or indirectly regulated
by SIM1. As shown by our work on Sim1, regulators of PVN development have the potential of influencing physiological processes.
The factors that will be identified in the course of this project may thus play a role in the pathophysiology of common disorders of
homeostasis.
Program/Abstract # 143
Do disruptions of a ZIC2 Non-coding Conserved Element cause Holoprosencephaly?
Barratt, Kristen S. (The Australian National University, Australia); Hu, Ping (National Human Genome Research Institute, USA);
Garrett, Lisa (Transgenic Core Facility, NIH, USA); Roessler, Erich; Muenke, Maximillian (National Human Genome Research
Institute, NIH, USA); Arkell, Ruth (The Australian National University, Australia)
Holoprosencephaly (HPE) is the most common structural malformation of the forebrain, sometimes presenting as cyclopia. Only 25%
of human HPE cases with normal chromosomes have been attributed to mutation of one of nine HPE associated genes, leaving 75% of
HPE cases with an unknown origin. Germline mutation of the transcription factor Zic2 causes HPE in both man and mouse and
recently variants in non-coding regions of ZIC2 have been considered a putative cause of HPE. Comparative genomics identified a
540bp Non-coding Conserved Element (NCE) in the ZIC2 3’UTR and screening of 528 human HPE probands isolated six variant
sequences in this NCE. None were identified in ethnically matched control populations, excluding that they are polymorphisms and
suggesting a contributing role in the development of HPE. We hypothesize that the identified NCE acts as an enhancer; a cis-acting
DNA regulatory element that stimulates transcription independent of its position or orientation. Interrogation of the NCE sequence
identified multiple transcription factor (TF) binding sites, some of which are altered in the six identified variants. Furthermore, ZIC2
HPE mutations are known to be loss of function, suggesting an enhancer role for the NCE in promoting ZIC2 expression during early
embryogenesis. We have shown that this NCE acts as an enhancer in transgenic zebrafish and mammalian cells and it is currently
being tested in transient transgenic mice. We aim to demonstrate that the ZIC2 NCE drives LacZ reporter expression during murine
embryogenesis, and that introduction of the identified variants alters reporter expression. We are also examining candidate TFs to
determine if they bind and regulate the ZIC2 NCE during gastrulation.
Program/Abstract # 144
A novel approach to study modulators of Wnt/beta-catenin pathway using Wnt reporter transgenic Xenopus and tailored-
TALENs mutagenesis
Tran, Hong Thi; Van Imschoot, Griet; Van Roy, Frans; Vleminckx, Kris (Ghent University, Belgium)
The Wnt/beta-catenin signaling pathway plays a crucial role during embryonic development and throughout adult life. Its aberrant
activation in human often results in the development of cancer. Although many domains of Wnt expression have been identified
during embryogenesis in Xenopus, the dynamics and the identification of the responding cells have been mostly unexplored due to the
lack of appropriate reporter tools. Previously, we have generated X. tropicalis transgenic reporter lines that express a dGFP variant
under control of a multimeric beta-catenin/TCF responsive element (Tran et al., 2010). dGFP is expressed in the transgenic lines in a
dynamic pattern throughout embryogenesis and reports general known domains of active Wnt signaling. Moreover, GFP patterns
identified a number of tissues as novel sites revealing previously unrecognized cell populations with beta-catenin/TCF dependent
transcriptional activity. These transgenic lines were proven to be reliable tool to study regulators of Wnt signalling. Recently, we have
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