Congress Abstracts - Society for Developmental Biology

have begun to document the targets of a large number of developmentally-active and tissue-restricted cardiac TFs, and mutant
versions, using the DamID technique and the HL-1 cardiomyocyte cell line, which beats homogeneously in culture. Our findings
suggest that ubiquitous TFs are embedded within the cardiomyocyte network at an executive level, and that mutant TFs bind a
surprising number of targets through co-factor interaction, including to hundreds of “off-targets” never seen by the wildtype factor and
which may play a role in congenital heart disease pathology.
Program/Abstract # 595
Defining mechanisms of imprinted expression at Igf2r/Airn during mouse gastrulation
Marcho, Chelsea; Bevilacqua, Ariana; Veeramani, Swarna; Mager, Jesse (Univ of Massachusetts-Amherst, USA)
Genomic imprinting is an epigenetic mechanism resulting in differential gene expression in a parent-of-origin manner. In the mouse
genome, there are approximately 100 imprinted genes, many of which occur in imprinted gene clusters. DNA methylation and histone
modifications have been shown to be allele specific at imprinted loci, corresponding with imprinted (allele specific) expression. At the
Igf2r/Airn cluster (which contains 3 maternally expressed genes Igf2r, Slc22a2, and Slc22a3), the paternally expressed non-coding
RNA Airn is thought to be responsible for silencing the paternal alleles of Igf2r, Slc22a2, and Slc22a3, resulting in reciprocal
imprinting at the locus. Here we examined the changes in imprinted gene expression in a tissue-specific and time-dependent manner
during gastrulation. We found that in embryonic tissue prior to gastrulation, Igf2r is biallelic and Airn is not expressed. Once
gastrulation commences, Igf2r and Airn become reciprocally expressed and imprinted. To examine the epigenetic mechanisms
involved in the establishment of Igf2r/Airn imprinting, we characterized changes in DNA methylation by bisulfite sequencing of two
differentially methylated regions (DMR) at the locus. Consistent with ES cell models, we found spreading of DNA methylation at
DMR2 during the start of gastrulation, corresponding to the changes in expression. Additionally, expression of CTCF, a factor
involved in imprinting regulation at the H19/Igf2 locus, is only present once gastrulation begins, suggesting CTCF may also play a
role in imprinting at Igf2r/Airn. Our data suggest a model similar to H19/Igf2 in which DNA methylation changes at onset of
gastrulation, blocking the binding of the methylation sensitive factor CTCF, which allows paternal Airn expression and silencing of
paternal Igf2r.
Program/Abstract # 596
Vascular plastic response in the primary somatosensory cortex of birth-enucleated rats
Silvia Zenteno De León, Raquel Martínez Méndez, Gabriel Gutiérrez Ospina (UNAM, México)
Blind individuals display an expansion of the primary somatosensory cortex (S1) and increments of its vascular density. Even though
both S1 expansion and increased vascular density in birth enucleated rats are thought to result from increased sensory experience, we
have recently published evidence that sensory experience is not increased in birth-enucleated rodents (Fetter-Pruneda et al., 2013). The
mechanisms leading to S1 vascular plasticity must then be carefully revised. We then evaluated vascular density in 7 days old (PD7)
and adult rats enucleated at birth and in those having intact sight. Although we confirmed previous results showing increments in
vascular density in the adult S1 of birth-enucelated rats, we were able to see such increments only in 20% of the sampled birth
enucleated rats at PD7. Interestingly, this change occurs when all birth enucleated rats had already displayed an expanded S1. Our
results thus support that increased vascular density is a consequence of S1 expansion in birth enucleated rats and that is not necessarily
related with increments in the inflow of sensory experience. Financial aid came from CONACYT 82879.
Program/Abstract # 597
Morphogenesis in the sea urchin: linking dynamically remodeling network states to protease function in development of
skeletogenic and non-skeletogenic mesoderm
Lyons, Deirdre C.; Dougherty, Mark; Saunders, Lindsay; McClay, David (Duke University, USA)
In the sea urchin embryo 64 Primary Mesenchyme Cells (PMCs) synthesize a calcium carbonate skeleton that defines the shape of the
larva. The PMC lineage comprises 4 cells at the vegetal pole in the early embryo. These cells then divide, invade the blastocoel via an
epithelial-to-mesenchymal transition (EMT), and undergo directed migration in response to ectodermal cues. Next, PMCs fuse
forming a syncytium within which the skeletal rudiment is secreted and subsequently elaborated by branching and elongation.
Previous research established a gene regulatory network (GRN) for PMC specification. We focus on uncovering subroutines
controlling morphogenetic processes. We and others identified subsets of transcription factors in the PMC GRN that are necessary for
behaviors such as cell invasion, migration, cell fusion and skeletal patterning. Using GRN analysis and time-lapse imaging we connect
these subnetworks to cell biological machinery proteins that carry out specific cellular processes. For example, metalloproteases are
necessary for invasion, migration and cell fusion in many cell types in other systems. We find that several families of metalloproteases
are dynamically expressed in the PMCs during EMT, migration and fusion, and are even expressed by certain PMC nuclei at the
growing rod tips. These patterns suggest a highly regulated spatiotemporal program of extra cellular matrix (ECM) modification by
the PMCs during successive step of differentiation. This work establishes the PMCs as a model for studying how a dynamically
remodeling GRN launches successive cellular behaviors within a single cell type. Furthermore, protease expression is also observed in
non-skeletogenic mesodermal cell types that are known to undergo later EMTs and remodel the ECM presumably to enable cell
migration and tissue fusion. Treating embryos with MMP inhibitors causes the PMCs to fail to make skeleton, and prevents proper
mouth formation and pigment cell differentiation, which involve non-skeletogenic mesoderm. These data suggest that proteases play a
171