Congress Abstracts - Society for Developmental Biology

it is still required to promote migration; however, later its functions is critical for the differentiation of the trunk neural crest
derivatives, in particular Rohon-Beard neurons.
Program/Abstract # 483
Further evidence that Id-proteins act through E-proteins: the Id-protein Extramacrochaetae regulates R7 cell fate through the
E-protein Daughterless in the Drosophila eye
Baker, Nicholas E.; Bhattacharya, Abhishek (Albert Einstein Coll Med, USA)
Our recent studies of Extramacrochaetae (Emc), an HLH protein that is the sole Drosophila representative of the Id gene family,
showed that a major role of Emc was to prevent daughterless (da), the sole Drosophila representative of the E-protein family of bHLH
genes, from autoregulating to high levels (Cell 147: 881-892, 2011). This seems to be a major part of preventing inappropriate
differentiation in Drosophila tissues, and of promoting differentiation at the proper times and places. Aspects of the same regulation
are seen in mammalian cells. The emc gene is also required for proper cell fate specification within the Drosophila eye. Without
emc, R7 cells develop as R1/6-like cells, and there are delays and deficits in differentiation of non-neuronal cone cells. These cell
fates also depend on Notch signaling, and previous studies indicated that emc was required for proper Notch signaling in these cells
and for expression of Notch target genes in the Enhancer-of-split Complex. Despite the fact that none of these cell types normally
depend on daughterless, we found that the effects of extramacrochaetae mutations were reverted in the absence of daughterless, so that
R7 cells and cone cells differentiated with apparently normal frequency and timing within clones of cells lacking both daughterless
and emc, and normal expression of the Notch target genes in the Enhancer-of-split Complex proteins was restored. These findings
establish that unchecked daughterless expression interferes with Notch signaling and precludes proper fate specification, and that
restraining daughterless expression and function is the crucial function of emc during R7 and cone cell development, just like the other
tissues we have studied, supporting the model that modulating E protein expression and function is the major function of Id proteins.
Program/Abstract # 484
EYA1/SIX1 drive neuronal developmental program in cooperation with the SWI/SNF chromatin-remodeling complex and
SOX2 in the mammalian inner ear
Xu, Pin-Xian; Ahmed, Mohi; Xu, Jinshu (Mount Sinai Sch Med, USA)
Inner ear neurogenesis depends upon the function of proneural basic helix-loop-helix (bHLH) transcription factors NEUROG1 and
NEUROD1. However, the transcriptional regulation of these factors is unknown. Using loss- and gain-of-function models, we show
that Eya1/Six1 are critical otic neuronal determination factors upstream of Neurog1/Neurod1. In mice lacking both Eya1/Six1,
Neurog1/Neurod1 are not expressed. Overexpression of both Eya1/Six1 is sufficient to convert nonneuronal epithelial cells within the
otocyst and cochlea as well as the 3T3 fibroblast cells into neurons. Strikingly, all the ectopic neurons express not only
Neurog1/Neurod1 but also mature neuronal markers such as neurofilament, indicating that Eya1/Six1 function upstream of and in the
same pathway as Neurog1-Neurod1 to not only induce neuronal fate but also regulate their differentiation. We demonstrate that
EYA1/SIX1 directly interact with the SWI/SNF chromatin-remodeling subunits BRG1 and BAF170 to cooperatively drive
neurogenesis in 3T3 cells and cochlear nonsensory epithelial cells, and that SOX2 cooperates with these factors to mediate neuronal
differentiation. Importantly, we show that the ATPase BRG1 activity is required for not only EYA1/SIX1-induced ectopic
neurogenesis but also normal neurogenesis in the otocyst. These findings indicate that EYA1/SIX1 are key transcription factors in
initiating the neuronal developmental program likely by recruiting and interacting with the SWI/SNF chromatin-remodeling complex
to specifically mediate Neurog1-Neurod1 transcription.
Program/Abstract # 485
Localization of Yap1 protein during blastocyst formation in the lab opossum
Spindler, Troy; Cruz, Yolanda (Oberlin College, USA)
Expression of transcription factor Cdx2 signals the specification of trophoblast in both eutherian (lab mouse) and metatherian (lab
opossum) blastocysts. In the mouse, this event depends on the simultaneous nuclear presence of Yap1 and TEAD4, known coactivators
of Cdx2. It has been shown that entry of Yap1 into the nucleus in the 8-16 cell stage is the proximate cause to the
stabilization of Cdx2 expression, while TEAD4 is constitutively present in the nucleus in mice. This suggests that the trophoblast
specification is ultimately guided by cell-cell contact through the Hippo signaling pathway (Niskioka et al., 2009). Using
immunofluorescent staining and confocal microscopy, we explored the possibility that trophoblast differentiation is likewise
dependent on the co-localization of Yap1 and Tead4 in the putative trophoblast nuclei of lab opossum embryos. We found that, in the
opossums, Yap1 is constitutively expressed in the nuclei of all blastomeres, contrasting with its dynamic expression in mice. This
indicates that the stabilization of Cdx2 expression and trophoblast differentiation is likely due to a different signaling pathway in
opossums.
Program/Abstract # 486
The Hippo pathway member Nf2 regulates inner cell mass/trophectoderm specification
Cockburn, Katie; Biechele, Steffen (Uof Toronto, Canada); Garner, Jodi (Sickkids Research Inst, Canada); Rossant, Janet (U of
Toronto, Canada)
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