Abstracts - Society for Developmental Biology

56
Program/Abstract # 170
Drosophila Zasp52 has a dual role in Z-disc maintenance and myofibril assembly
Katzemich, Anja; Schoeck, Frieder, McGill University, Montreal, Canada
Zasp52 is a multi-domain protein, composed of an N-terminal PDZ domain, ZM motif, and four LIM domains, and is
found predominantly in Drosophila muscle. It is part of the PDZ-LIM domain protein family, which comprises Enigma,
ENH, ZASP, Alp, CLP36, RIL, and Mystique invertebrates. In Drosophila embryos, Zasp52 was shown to co-localize
with alpha-actinin at Z-discs and with integrins at myotendinous junctions. Mutations in Zasp52 cause first in star larval
lethality with defects in Z-disc assembly and maintenance as well as muscle attachment. During Drosophila indirect flight
muscle (IFM) development in the pupa, Zasp52 is present at very early stages of myofibril assembly. It localizes with
alpha-actinin in rudimentary Z-bodies along the assembling myofibril, before other muscle proteins show any periodicity.
Live imaging of endogenous GFP-Zasp52 also demonstrates that Zasp52 is present in the developing Z-disc throughout
embryonic myofibrillogenesis. RNA interference against the last exon encoding the most C-terminal LIM domain results in
the depletion of all high molecular weight isoforms. This gives rise to viable but flightless adult animals. IFM sarcomeres
show thin and interrupted Z-discs as well as distorted H-zones. In some regions of the IFM, sarcomeres were torn apart
severely. These findings suggest that Zasp52 is required for the establishment of normal Z-discs in the IFM and subsequent
sarcomere stability after onset of contractility. We will propose a model of IFM myofibril assembly based on electron
microscopy, confocal microscopy and live imaging of IFM development in wild type and Zasp52 mutants.
Program/Abstract # 171
Sulf1 modulates FGF and BMP signaling to pattern trunk muscle, pigmentation, and lateral line
Meyers, Jason; Planamento, Jessica; Krulewitz, Neil, Colgate University, Hamilton, United States; Pownall, Mary
(University of York, York, United Kingdom)
Heparan sulfate proteoglycans (HSPGs) are glycosylated extracellular or membrane-associated proteins. The sulfated
domains of heparan sulfate polysaccharide chains can interact with many growth factors and receptors, modifying their
activity or diffusion. The pattern of sulfation can be modified by secreted extracellular sulfatases, which remove specific
sulfates from the heparan sulfate chains. Changes in sulfation patterns can change growth factor gradients and activities,
thus precise expression of sulfatases is believed to be necessary for normal development. We have examined the role of the
sulf1 gene, which encodes a 6-O-endosulfatase, in trunk development of zebrafish embryos. Sulf1is expressed in the
developing trunk musculature and notochord. Knockdown of sulf1 with antisense morpholinos results in a lack of a
myoseptum, improper pigmentation along the mediolateral stripe, and improper migration of the lateral line primordium.
All of these phenotypes are consistent with alteration of signaling along the myoseptum. Sulf1 knockdown results in a
decrease in muscle pioneer cells and loss of sdf1 expression along the mediolateral trunk musculature, but these can be
rescued by pharmacological inhibition of BMP signaling, which also restores pigmentation patterning. Lateral line
migration and deposition depend on proper sdf1 expression and FGF signaling respectively, both of which are disrupted in
sulf1 morphants. Pharmacological activation of FGF signaling can rescue proper spacing of neuromast deposition in these
fish. Together this data suggests that sulf1 serves a crucial role in modulating both BMP and FGF signaling to allow proper
morphogenesis of trunk musculature, pigment cells, and lateral line neuromasts.
Program/Abstract # 172
Prox1 modulates the neuromast deposition frequency in the migrating posterior lateral line primordium
Yoo, Kyeong-Won; Dalle-Nogare, Damian; Chitnis, Ajay, NICHD/NIH, Bethesda, United States
Mechanosensory organs called neuromasts in zebrafish are generated by periodical deposition from the trailing end of
migrating posteriorlateral line primordium (pLLP) as it migrates from the otic vesicle to the tip of the tail. The longevity of
the migrating primordium is maintained by the activity of Wnt effector, Lef1, in the leading zone of primordium. In
contrast, formation, maturation of proto-neuromasts and its deposition is regulated by the activity of FGF signaling in the
trailing zone. In this study we have examined the role of the homeo domain transcription factor Prox1 in the migrating
pLLP. Prox1 is broadly expressed in the pLLP, which contains 2-3 proneuromasts at progressive stages of maturation. Its
expression is driven by dual signaling system of Wnt signaling in the leading zone and FGF signaling in the trailing zone.
Knockdown of prox1 with morpholinos showed the less frequent deposition of neuromasts and delayed formation and
maturation of proto-neuromasts in the pLLP. These changes were associated with expanded expression of Wnt effector
lef1 and reduction of pea3, target gene of FGF signaling, in the pLLP. Our results suggest a previously unaddressed role
for Prox1 in switching between Wnt and FGF signaling determining the frequency of neuromast deposition in the pLLP.