Abstracts - Society for Developmental Biology

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thyroid adenoma associated protein, THADA, putatively involved in TRAIL-induced apoptosis thus in mediating the
steady state between cell death and proliferation. Through this and future work, we are beginning to identify the key
“stemmness” factors that truly represent regulators of regeneration.
Program/Abstract # 199
MicroRNA mediated regulation of naïve and primed pluripotent states
Pernaute, Barbara, National Heart and Lung Institute, Imperial College London, London, United Kingdom; Spruce,
Thomas (MRC National Institute for Medical Research, London, United Kingdom); Manzanares, Miguel (Centro
Nacional de Investigaciones Cardiovasculares-CNIC, Madrid, Spain); Rodriguez, Tristan (National Heart and Lung
Institute, Imperial College London, United Kingdom)
Two distinct phases of pluripotency have been proposed in the early mammalian embryo, a naïve state found in the epiblast
of the 3.5 days post coitum (dpc) mouse embryo and in embryonic stem cells (ESCs) and a primed state, found in the
epiblast of the 5.5-6.5 dpc embryo and in epiblast stem cells (EpiSCs). These two states of pluripotency are thought to be
regulated by different mechanisms as different combinations of growth factors are required for their maintenance both in
vivo and in vitro. MicroRNAs (miRNAs) are small non-coding RNAs that repress gene expression post-transcriptionally.
In ESC miRNAs are required for proper proliferation and for exit from the naïve pluripotent state, however little is known
about their roles in the primed phase of pluripotency. We have found that in contrast to the naïve pluripotent state in the
primed pluripotent state miRNAs are required for cell survival but not for the initiation of differentiation, either in vitro or
in vivo. Profiling in embryos from 5.5 dpc to 8.5 dpc has identified four miRNA families that account for over 75% of the
total miRNA content at these stages. These miRNAs show dynamic expression during the initial phases of epiblast
differentiation and are likely to be responsible for the defects observed in embryos and EpiSCs lacking miRNAs. This
work provides insight into how miRNAs regulate the different pluripotent states and contributes to the understanding of the
regulatory networks involved in stem cell homeostasis, pluripotency and differentiation during early embryo development.
Program/Abstract # 200
Examining the evolutionarily conserved functions of Piwi proteins in Hydra
Lim, Robyn, Temasek Life Sciences Laboratory, Singapore, Singapore; Nishimiya-Fujisawa, Chiemi (National Institute
for Basic Biology, Okazaki, Japan); Kai, Toshie (Temasek Life Sciences Laboratory, Singapore, Singapore)
Piwi proteins and their associated Piwi-interacting RNAs (piRNAs) are evolutionarily conserved, having been observed
throughout the animal kingdom to participate in stem cell regulation and preserving genetic integrity. In the vertebrates and
ecdysozoans investigated thus far, Piwi proteins and piRNAs are highly enriched in the germline. Interestingly, Piwi
proteins are expressed in the multipotent or totipotent stem cells of other bilaterians and in non-bilaterian animals,
implying a wider role of such genes throughout the animal kingdom than previously thought. More importantly, this
suggests an ancestral significance of Piwi protein functions in stem cells. We have generated antibodies against two Piwi
orthologs, Piwi1 and Piwi2, in the basal metazoan, Hydra. Both Piwi proteins are specifically expressed in the interstitial
stem cells—multipotent stem cells that give rise to somatic and germline lineages—and localize to perinuclear foci which
are largely reminiscent of the nuage. This organelle has been implicated as a site for piRNA-mediated transposon silencing
and the ping-pong amplification loop of piRNA biogenesis. Piwi1 and Piwi2 foci are frequently observed to colocalize or
collocate with each other, suggesting that piRNA biogenesis via ping-pong amplification might be taking place between
the two Hydra Piwi proteins. Both Piwi1 and Piwi2 foci progressively diminish in size and intensity in differentiating
intermediates of the interstitial cell lineage and are not observed in fully differentiated cells. Our preliminary data suggests
that piwi2 is involved in the maintenance of interstitial stem cells. We have also isolated piRNAs from Hydra and the
piRNA population which is bound to Piwi2.
Program/Abstract # 201
Forward genetics identifies Edf1 as a novel regulator of epidermal development and stem cell quiescence
Lee-Wölfel, Sunjin; Kong, Yong; Weatherbee, Scott, Yale University, New Haven, United States.
The outermost layer of the skin, the epidermis, plays a key role in animal survival by acting as a barrier to prevent infection
and desiccation. Stem cells in the interfollicular epidermis (IFE) undergo a series of cell fate choices during the
differentiation program to form a stratified epidermis. The appropriate balance between proliferation and differentiation is
crucial for epidermis function, and alterations in this process can cause human diseases, such as psoriasis and skin cancer.
However, the factors that regulate cell fate choices of stem cells in the IFE are not well understood. To identify new
mediators involved in these processes, we performed a forward genetics screen in mice and identified a novel regulator of
skin development, the Epidermal differentiation factor 1 (Edf1) gene. Mice carrying a homozygous mutation in Edf1
develop a hyperproliferative, poorly differentiated epidermis. We have shown that Edf1 function is essential to curb stem