Congress Abstracts - Society for Developmental Biology

shape, similar to the Arp2/3 loss of function phenotype, the main actin nucleator in the lamellipodia formation. Accordingly,
molecular markers exhibited similar distribution in PRPK and Arpc4 (Arp2/3 complex subunit) knockdown hemocytes. Interestingly,
functional interaction assays revealed that Rac1 and Rab35 co-expression, both proteins with demonstrated lamellipodia inducing
capacity, attenuated the PRPK knockdown phenotype. Further, Rac1 overexpression phenotype was suppressed by PRPK loss of
function. Finally, PRPK deficient hemocytes have decresed phagocytic ability in culture. Our results suggest that PRPK is critical in
lamellipodia structuration, a necessary protrusion to right immune cell function. Funding: FONDECYT 1100366, FONDAP 15090007
Program/Abstract # 59
Alterations in Ptch1 Cis-Regulation underlie loss of antero-posterior identity and digit reductions in bovine limbs
Rolf Zeller (U Basel, Switzerland); Amandine Duchesne (Jouy en Josas, France); Sepziale Dario (Basel, Switzerland); Guillaume
Andrey (Lausanne, Switzerland); Erkan Uenal, Christian Basel (Basel, Switzerland); Benoit Robert (Paris, France); Carol Wicking
(Brisbane, Australia); Denis Duboule (Lausanne, Switzerland); Javier Lopez-Rios (Basel, Switzerland)
Bovine limbs exemplify the skeletal diversification and digit reductions that occurred during evolution of the artiodactyl clade.
Comparative functional analysis of mouse and bovine embryos reveals the limb-specific molecular alterations that underlie this
morphological variation. No overt differences are detected in establishment of the anterior-posterior (AP) asymmetry and the
morphoregulatory signaling system interactions during the onset of limb bud outgrowth. Subsequently, the mesenchymal expression
of key genes becomes rather apolar, which indicates that the initial AP asymmetry is lost during progression of bovine limb bud
development. Genetic analysis has established that up-regulation of Ptch1 expression in the mesenchymal cells responding to SHH is
crucial to normal mouse limb development. In spite of the increase in Shh expression, Ptch1 remains very low in the mesenchyme of
bovine limb buds. Furthermore, Gli1 expression in bovine limb buds is consistent with a failure in Ptch1-mediated sensing of graded
SHH signaling in the mesenchyme. 4C-Seq analysis of mouse limb buds and sequencing of the Ptch1 locus from different artiodactyl
species identified a candidate limb bud cis -regulatory region, which is significantly and specifically divergent when comparing
artiodactyl and pentadactylous species. Transgenic analysis shows that the mouse cis-regulatory region drives expression of a LacZ
reporter into the posterior-distal mesenchyme. The functional importance of this transcriptional alteration was evidenced by analysis
of mouse limb buds lacking mesenchymal Ptch1, which results in molecular changes strikingly similar to the expression patterns
observed in bovine limb buds.
Program/Abstract # 60
The development and evolution of oxygen-sensing cells
Dorit Hockman (U Cambridge, UK); Alan Burns (Univ College London Inst of Child Health, UK); Alessandro Mongera (Max-Planck
Institut für Entwicklungsbiologie, Germany); Shannon Fisher (U Pennsylvania, USA); Knapik, Ela (Vanderbilt, USA); Robert Kelsh
(U of Bath, UK); Clare Baker (U Cambridge, UK)
Oxygen-sensing cells involved in the respiratory reflex develop in association with the embryonic pharyngeal arch arteries and gut
endoderm. In the adult, oxygen-sensing cells are located in the carotid body and lungs of amniotes, and in the gills and orobranchial
cavity of anamniotes. These cells respond to hypoxia in the blood and surrounding air/water, triggering increased ventilation via the
respiratory reflex. Despite their physiological importance, little is known about their development or evolution. The oxygen-sensing
cells of the gills, which develop in association with pharyngeal arch arteries, are hypothesised to be evolutionarily related to those of
the carotid body, which are neural crest-derived and develop in association with the third pharyngeal arch artery. However, this
relationship has never been tested. Using neural fold grafts in the chick and genetic lineage-tracing in the mouse, we confirm the
neural crest origin of the carotid body, and also show that the oxygen-sensing cells of the lungs are not neural crest-derived. Using
vital dye labelling, neural fold grafts, genetic lineage-tracing and analysis of zebrafish mutants lacking all neural crest cells, we show
that the oxygen-sensing cells in the gills and orobranchial cavity of lamprey, zebrafish and frog are not neural crest-derived. Hence
these cells cannot share an evolutionary origin with carotid body glomus cells. Our results suggest that oxygen-sensing cells in the
lungs, not the carotid body, are homologous to those found in the gills and orobranchial cavity of anamniotes, and, furthermore, that
the importance for the respiratory reflex of hypoxia-sensitive neural crest-derived cells seems to have evolved in association with airbreathing.
Program/Abstract # 61
The evolution and development of leaves in lycophytes and ferns
Barbara A. Ambrose, Alejandra Vasco, Tynisha Smalls, Robbin Moran (NY Botanical Garden, USA)
There is a vast amount of leaf morphological diversity and leaves are a common feature found across the land plants. However, not all
land plant leaves are considered homologous. The fossil record and anatomical evidence suggest that leaves evolved at least 4 times
independently in vascular land plants. Molecular genetic studies have unraveled the network underlying the development of
flowering plant leaves and some comparative studies have been performed in lycophytes. However the experimental results in the
lycophytes have led to diametrically opposed conclusions about the conservation of a common leaf developmental network between
lycophytes and flowering plants. These studies focused on Class III HD-Zip and Class I KNOX genes. To better understand the role
of these genes in leaf evolution and development we are cloning and analyzing genes from these 2 key transcription factor families
across the lycophytes and ferns . In addition, we are analyzing key leaf genes in a monophyletic group of fern species, Elaphoglossum
section Squamipedia , to better understand the evolution and development of leaves in this group that have widely divergent leaf
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