Abstracts - Society for Developmental Biology

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doses led to inhibition in cell movements while a percentage of the embryos showed abnormal tissue separation. These
observations suggest that, in addition to its potential teratogenic effect on head development, retinoic acid has also a
positive regulatory role in head induction during early gastrula. This novel activity ofretinoic acid signaling is in agreement
with the proposed reduction of this signal in syndromes exhibiting craniofacial malformations.
Program/Abstract # 345
The role of maternal Dpp/BMP pathway in the early Drosophila embryo.
Fontenele, Marcio; Pentagna, Nathalia; Araujo, Helena, Federal University of Rio de Janeiro, Brazil
Dorsoventral (DV) patterning in Drosophila melanogaster is regulated by the Toll pathway by modulating Cactus/IkB
protein degradation, and thus nuclear Dorsal/NFkB protein levels in the early embryo. In addition to the Toll pathway,
through previous genetic and biochemical studies we have shown that the maternal Dpp/BMP pathway regulates nuclear
Dorsal levels by controlling Toll-independent degradation of Cactus. The maternal Dpp pathway requires Calpain A, a
calcium-activatedcysteine protease, to target Cactus degradation and thus to regulate Dorsal levels. Using a Real-time
qPCR approach we have shown that the maternal Dpp pathway regulates mRNA levels of CalpainA and Casein Kinase II
in the earlyembryo. These results suggest that maternal Dpp functions through a novel mechanism, since the effects of Dpp
blockage are observed before the onset of zygotic transcription. This raises the possibility that the maternal Dpp/BMP
pathway acts through post-transcriptional mechanisms to regulate stability or degradation of mRNAs. Accordingly, null
germline clones for the tkv type I receptor, mad or medea SMADs generate DV patterning defects similar to those reported
for blockage of the tkvreceptor. In order to define the functional role of maternal Dpp on mRNA levels we have
undertaken a qPCR approach. Recent data reveals that we are able to detect variations in mRNA levels in the preblastoderm
embryo upon blockage of maternal Dpp signals. The results obtained up to now suggest that Dpp regulates
maternal mRNA levels in the embryo. We are currently exploring whether some of these maternal mRNAs participate with
Dpp to regulate discrete nuclear Dorsal levels and thus DV patterning. This work is supported by CNPq, Pronex, FAPERJ
and INCT-EM.
Program/Abstract # 346
Split top: A maternal regulator of dorsal-ventral patterning and cell migration in zebrafish
Langdon, Yvette G., University of Pennsylvania Cell and Development, Philadelphia, United States; Gupta, Tripti
(Cambridge, United States); Marlow, Florence (Bronx, United States); Abrams, Elliott (Philadelphia, United States);
Mullins, Mary (Philadelphia, United States)
Maternal factors are required for many early developmental processes including fertilization, egg activation, and formation
of the body axes during embryonic development of the zebrafish, Danio rerio. Our lab has performed a recessive maternaleffect
mutagenesis screen and identified a number of mutants with defects in early developmental processes, including
early morphogenesis and body axis formation. One such mutant, Split top exhibits abnormal dorsal-ventral patterning,
displaying a dorsalization of the embryonic axis. Clutches of embryos from Split top mutant mothers are characterized by
the five classic dorsalized phenotypic classes, as well as some additional defects. The mutant embryos show an expansion
of dorsal markers and a corresponding reduction in ventral markers during gastrulation indicative of dorsalization. The
additional defects appear to be the result of altered morphogenesis, including defects in epiboly, the process by which the
blastoderm cells migrate over and surround the yolk. Split top mutant embryos also appear to be defective in the cell
movement process of convergence and extension. We mapped the Split top mutation to chromosome 17, within a 1 MB
interval and efforts are currently underway to positionally clone the affected gene.
Program/Abstract # 347
Oocyte asymmetry and the animal-vegetal axis in zebrafish
Marlow, Florence; Heim, Amanda; Rothhamel, Sophie; Hartung, Odelya; Schwartz-Orbach, Lianna; Jenny, Andreas,
Albert Einstein College of Medicine, New York, United States
The vertebrate animal-vegetal axis is established during oogenesis. Oocyte polarity is pre-requisite for determining the
prospective embryonic axes and setting aside the germ cell determinants in non-mammalian vertebrates. The Balbiani body
is an evolutionarily conserved oocyte asymmetry present in early oocytes of allanimals examined, including humans.
However, bucky ball is the only gene known to be essential to establish oocyte polarity in vertebrates. Lack of maternal
Buckyball causes failure to specify oocyte asymmetry and the embryonic axes through an unknown pathway and
mechanism. To investigate how Bucky ball regulates asymmetries in oocytes we are testing the hypothesis that buc
specifies the oocyte axis upstream or at the level of Balbiani body assembly. We have identified candidate components of
the Buc pathway through yeast genetic and affinity purification approaches. To identify regions of Buc protein with
potential functional significance we have mapped the regions of the Buc protein that mediate interactions with its binding