Abstracts - Society for Developmental Biology

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division, but rapidly loses its pericentriolar material and does not reduplicate during the S-phase of the first endocycle.
SPD-2 then translocates to the nucleus where it is eventually eliminated. We observed that modification of a highly
conserved CDK-phosphorylation site to non-phosphorylable residue on SPD-2 resulted in the failure of the centriole to
duplicate before the intestinal nuclear division. Alternatively, mimicking PLK-mediated phosphorylation of SPD-2 or
reducing the activity of ubiquitination pathway leads to its nuclear accumulation likely through stabilization. Overall our
study reveals that phosporylation of SPD-2 by key cell cycle kinases may regulate centriole/cell cycle uncoupling and
elimination during C. elegans development. We are currently investigating whether these modifications are conserved in
various developmental contexts and/or in other species.
Program/Abstract # 89
Profiling expression of cell cycle regulators during zebrafish development.
Dobbs-McAuliffe, Betsy L., Central Connecticut State Univ Biomolecular Sciences, New Britain, United States
Embryonic development depends upon cellular proliferation and terminal cell differentiation. These processes can be coregulated,
as cells that enter terminal differentiation stop dividing. We believe that many of the factors that promote
terminal differentiation couple these events by altering expression of cell cycle regulators. We wanted to explore this
hypothesis while providing independent research projects for undergraduate students. Students were trained in one
technique, in situ hybridization, and then executed segments of the study. To this end, we have begun a detailed analysis of
expression of cell cycle regulators in the zebrafish embryo. Since we are particularly interested in the timing of cell cycle
exit we have initially focused on expression of the cell cycle inhibitors cdkn1b (p27 kip1) and cdkn1c (p57 kip2). We are
detailing normal gene expression through 24h of development. Additionally we are monitoring expression of cell cycle
regulators in embryos where specific signaling pathways have been altered. To start we investigated expression of cell
cycle inhibitors in embryos that lack Hedgehog signaling. We have found that cdkn1c, which is normally expressed both in
slow muscle and in primary neurons, requires Hedgehog signaling in the slow muscle, but not in the primary neurons.
Previous research has shown that slow muscle precursors switch fate to fast muscle in the absence of Hedgehog signaling.
We suspect that slow muscle precursors will show a concomitant switch to expression of cdk1nb, the cell cycle inhibitor
expressed in fast muscle. Another target of our studies is the retinoic acid (RA) signaling pathway. Preliminary results
suggest that RA down regulates cdkn1c expression in the somites.
Program/Abstract # 90
Barhl2 contribute to a cell-intrinsic mechanism that limits the proliferative response of neural progenitors to their
mitogen.
Durand, Béatrice; Juraver-Geslin, Hugo; Duval, Nathalie, CNRS UMR, Paris, France
The gene networks that underpin the overall, and differential, growth of our future brain are still poorly understood. We
showed that, in Xenopus embryos, Barhl2 limits the proliferation of diencephalic neural progenitors, via the regulation of a
CASPASE-3 unconventional activity that inhibits the activation of the major effector of the Wnt canonical pathway, ß-
catenin. We showed that Barhl2 expression domains are highly similar in the developing mouse and Xenopus CNS: in
both, it is expressed in association with Wnt3A and Shh which both promote neuroepithelial proliferation. Barhl2 is
coexpressed with Wnt3A in the cortical hem, the cerebellar primordium and in asubset of granule cell progenitors (GCP), a
cell population characterized by aprolonged proliferation period. At postnatal stages, Barhl2 is expressed in the cerebellar
sulci where the SHH pathwayis most active. We examined whether Barhl2 contributes to intrinsic mechanisms that locally
attenuates the GCP proliferative response to their most potent mitogen SHH. To perform loss of function experiments we
generated lentiviral vectors that deliver shRNA which silence Barhl2 expression with high efficiency. These vectors allow
for efficient and stable Barhl2 silencing in neurons, their progenitors and other neural cell types with no toxicity. We
demonstrated that Barhl2 cell-autonomously limits SHH-stimulated GCP proliferation and decreases the dependence of
GCP proliferation on SHH. Our results indicate that Barhl2 expression pattern is conserved across species and associated
with « mitogeniccenters », and argue that Barhl2 plays a conserved role in the local control of neuroepithelial growth.
Program/Abstract # 91
Identification and expression analysis of two homologs from Xenopus laevis of the Tumorhead putative binding
protein, FBXO30
Traverso, Edwin, University of Puerto Rico at Humacao, United States; Zbinden, Theodor (Univ of Puerto Rico, Rio
Piedra, PR, United States); Flores, Noelia; Núñez, Dariana; Ayala, Jesús (University of Puerto Rico at Humacao,
Humacao, PR, United States)
Tumorhead (TH) is a maternal factor that regulates cell proliferation during early embryogenesis in Xenopus laevis. To
understand how TH functions at the molecular level, we have been studying its relationship with the novel F-Box