Congress Abstracts - Society for Developmental Biology

The inner ear contains the sensory organs for the hearing and balancing and is embedded within the cephalic mesoderm of the embryo.
However it is induced by fibroblast growth factor signals as an epithelial placode in the surface ectoderm adjacent to the posterior
hindbrain. In the chick, the inner ear placode first becomes morphologically apparent as a thickening of the ectoderm. It then gradually
invaginates to form an otocyst within the head mesenchyme. We have previously showed that basal fibroblast growth factor (FGF)
signalling acting through phospholipase Cγ activates basal myosin II. Myosin II exhibits a non-canonical activity that results in the
local depletion of actin filaments and thus causes the basal expansion of the otic placode. Subsequent to basal expansion of the inner
ear placode, apical constriction drives to complete invagination. We find that the small GTPase protein, RhoA is localized apically and
activation of RhoA increases gradually during inner ear morphogenesis. Our data provide evidence that RhoA play bi-functional roles
to trigger apical constriction of the otic epithelia and likely, this is FGF independent process. Firstly, RhoA regulates the assembly of
junctional actin filaments. Secondly, RhoA controls the apical activation of myosin light chain, the active component of Myosin II. I
describe the detail molecular pathway involved in RhoA-coordinated apical constriction during otic morphogenesis.
Program/Abstract # 298
Convergent evolution of cellular immunity in jawless fish
McCurley, Nathanael; Guo, Peng; Cooper, Max (Emory University, USA)
Adaptive immune reactions require a complex choreography of molecules, cells, and tissues, yet this form of immunity appeared
suddenly in evolution with the emergence of the vertebrates. The jawless vertebrates (lampreys and hagfish), however, lack the key
antigen receptor genes that mediate adaptive immunity in the jawed vertebrate lineage. Instead, jawless vertebrates use a novel gene
family encoding leucine-rich repeat proteins that are somatically diversified, monoallelically expressed on lymphocytes, and used as
antigen receptors in adaptive immune reactions. These variable lymphocyte receptors (VLRs) are generated during lymphocyte
development by a stochastic gene assembly process resulting in a potential antigen receptor repertoire of >10 14 . Our lab identified a
VLR lymphocyte population in lampreys (termed VLRA cells) that resembles the T cells of jawed vertebrates by numerous
parameters that include development in the recently characterized lamprey thymus equivalent. The nature of the antigen recognized by
VLRA receptors remains unknown, though current data suggest that they bind processed antigens. We hypothesize that VLRA cells
are involved in cellular immune responses, possibly through recognition of antigen presented in the context of histocompatibility
determinants. We devised several experimental approaches to test this hypothesis and our data indicate that VLRA cells respond
preferentially to allogeneic stimulation, suggesting a role in cellular immunity. We furthermore used allogeneic immunization to
develop antisera that recognize lamprey allodeterminants on myeloid leukocytes, consistent with the hypothesis that these cells
express the antigen that drives allogeneic responses.
Program/Abstract # 299
Comparative analysis of the colon in the vertebrate lineage.
Theodosiou, Nicole; Wechter, Todd; Jain, Meaghan (Union College, USA)
During the aquatic to terrestrial transition, vertebrates were challenged by dehydration once on land. The development of a colon
allowed tetrapods to maintain water homeostasis and prevent desiccation. In contrast to beliefs that a colon evolved after tetrapod
evolution, a rudimentary colon exists in the cartilaginous fish Leucoraja erinacea (skate) and Squalus acanthias (dogfish). This is
surprising because elasmobranchs appeared 450 mya, and thus predate the transition from aquatic to terrestrial life (approximately 370
mya). To understand if elasmobranchs were pre-adapted for conserving water prior to the tetrapod transition, the digestive tracts of
representative species from gnathostomes and ray-finned fish are being examined for colon developmental markers and histology. The
lamprey Petromyzon marinus contains a discreet region in the distal intestine with elevated levels of acid mucin-producing goblet
cells, cell markers for the colon. A similar region with colon-like cells is found in the distal intestine of the ray-finned fish Polyodon.
In addition, there is a dorsal-ventral asymmetry to the acid mucin distribution in the lamprey and paddlefish. The dorsal-ventral
asymmetry in lamprey and paddlefish suggests a common origin for the colon in vertebrates. However, the asymmetry is not observed
in different species of elasmobranchs suggesting that a rudimentary colon may have been advantageous to elasmobranchs, allowing
them to adapt to different environments with changing salinities. Together these data suggest that the colon arose prior to the tetrapod
transition and expanded in the vertebrate lineage.
Program/Abstract # 300
The role of lbx1 during Xenopus and Nematostella embryogenesis – a comparative study of myogenesis in metazoans
Strobl, Anna-Christina (NIMR MRC, UK) Steinmetz, Partick; Fredman, David; Technau, Ulrich (University of Vienna, Austria);
Smith, Jim (NIMR MRC, UK)
In vertebrates, one of the main tissues derived from the mesodermal germ layer is muscle. The early branching metazoans, however,
lack mesoderm, and their muscle derives from the endoderm. We are studying the evolutionary relationship between cnidarian and
vertebrate myogenesis to improve our understanding of the mechanisms regulating muscle development. Although the cnidarian
Nematostella vectensis does not possess mesoderm, many ‘mesodermal’ transcription factors are encoded in its genome. We dissected
the function of one such gene, the NK-homeobox transcription factor ladybird (lbx1), which is involved in muscle formation in both
Nematostella and Xenopus. Morpholino-mediated knockdown of Nvlbx1 results in changes of endodermal morphology, probably due
to loss of mesenteric muscle cells. This indicates that Nvlbx1 regulates endoderm differentiation and in particular muscle formation in
Nematostella. By using RNA-Seq to identify genes that are up- or downregulated in Nematostella Nvlbx1 morphants, we have gained
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