Page 77 - Mouse Molecular Genetics

Full Abstracts
Program number is above title. Author in bold is the presenter.
mutants display aberrant cell packing along with diminished actin polymerization and filopodia
formation in SHF progenitors in the caudal SpM, where Wnt5a and Dvl2 are co-expressed specifically. Based on these results,
we propose a novel model in which a Wnt5aDvl PCP signaling cascade promotes SHF deployment by promoting actin
polymerization and protrusive cell behavior to continuously recruit SHF progenitors into a cohesive sheet in the caudal SpM,
thereby pushing the SpM rostrally into the OFT.
Transcriptional Mechanisms Underlying Sonic Hedgehog Mediated Regulation.
Qiang Li, Jordan P. Lewandowski, Marian
Steven A Vokes
Molecular Cell & Developmental Biology, University of Texas at Austin, Austin, TX.
The Sonic hedgehog (Shh) pathway plays critical roles in development and cancer. All Shh activity is mediated by Gli proteins,
which act as context-dependent transcriptional activators or repressors in the presence or absence of Shh pathway stimulation.
According to current models, the ratio of Gli-activator to repressor forms gives rise to a quantitative transcriptional output. While
several studies have persuasively demonstrated a quantitative role for Gli-activator activity, the role of Gli-repressors remains
poorly understood. We identified a long-range Gli binding site in the Gremlin locus that has Gli-dependent enhancer activity in
transgenic embryos, and exhibits a spatiotemporal pattern consistent with control by Shh. To determine how this domain is
regulated by Gli activator and repressor forms, we examined its activity in a number of different Shh pathway mutants. Our
results suggest that the enhancer domain requires Gli-activator activity but is not repressed anteriorly by Gli-repressor forms. In
light of these results, we were surprised to find that Gli repressor binding to the enhancer does play a direct role in preventing
ectopic Gremlin transcription by repressing activity from other cis-regulatory domains. Together, our results suggest a model for
Shh-directed transcription where the Gli-bound cis-regulatory domain acts a toggle switch to impose Gli-dependent control over
genes with multiple cis-regulatory domains.
Engrailed genes regulate regional cerebellum growth by modulation of hedgehog signaling. Ryan Willett
Joyner. Developmental Biology, Memorial Sloan-Kettering Cancer Center, New York, NY.
The cerebellum (Cb) is a foliated posterior brain structure involved in coordination of motor movements, motor learning,
balance, and cognition. Although morphologically and functionally complex, the simple layered cytoarchitecture of the cortex
makes the Cb an ideal model for studying neurodevelopmental processes. During the first 2 postnatal weeks, the Cb undergoes
rapid growth driven by proliferation of granule cell precursors (GCPs) in the external granule cell layer (EGL). GCPs then
differentiate into granule cell (GC) neurons and migrate to form the inner granule cell layer (IGL). The engrailed family of
homeobox transcription factors (referred to collectively as EN1/2), are key regulators of mouse cerebellum development
including regionalization, patterning, morphogenesis, growth, and assembly of neural circuitry. En1 null mutants do not form a
midbrain or Cb, whereas loss of En2 results in a small Cb with altered foliation. We recently found that conditional deletion of
En1 and En2 in GCPs (Atoh1-Cre/+; En1fx/fx; En2fx/fx or RLd-Cre; En1/2) results in a Cb with pronounced hypoplasia but
normal cytoarchitecture and only a mild foliation defect (Orvis, 2012). Analysis of cell death in these mutants has revealed a cell
non-autonomous decrease in survival and delay in maturation of Purkinje cells (PCs). Since SHH, produced by PCs, is a major
mitogen for GCPs we examined whether this pathway is altered during postnatal Cb growth in RLd-Cre; En1/2 mutants.
Interestingly, we found that En1/2-deficient EGL cells exhibit altered SHH signaling, which had cell autonomous and non-
autonomous components. Gli1 expression, a readout of SHH pathway activation, was elevated in the EGL of the anterior zone of
the Cb but markedly reduced throughout the central zone in the mutant Cb. Interestingly, central zone morphology was most
affected in the RLd-Cre; En1/2 Cb as the appearance of three fissures that surround the folia was delayed and the ultimate depth
was reduced in the region of reduced Gli1 expression. Strikingly, GCPs isolated from RLd-Cre; En1/2 Cb showed a Smo-
dependent enhancement of proliferation in the absence of SHH despite a normal proliferative response to recombinant SHH in
culture. This result suggests that En1/2-deficient GCPs are sensitized to a trace amount of SHH in the medium or have SHH-
independent growth activity. Our study indicates that EN1/2 function in RL-derived cells to coordinate SHH pathway activity
during Cb growth.
An Lmx1b-miR135a2 Regulatory Circuit Modulates Wnt1/Wnt Signaling and Determines the Boundaries of the
Midbrain Dopaminergic Progenitor Pool.
Angela Anderegg
Hsin Pin Lin
Jun An Chen
Natalya Cherepanova
Randy Johnson
Jason Rock
Brian Harfe
Raj Awatramani
. 1)
Northwestern University, Chicago, IL; 2)
Academia Sinica, Taipei, Taiwan; 3) MD Anderson, Houston, TX; 4) U of Florida, Gainsville, FL.
MicroRNAs function to regulate gene expression in diverse physiological scenarios. Their role in the control of morphogen
related signaling pathways has been less studied, particularly in the context of embryonic CNS development. Here, we uncover a
role for microRNAs in limiting the spatiotemporal range of morphogen function. Wnt1 is a key morphogen in the embryonic