Abstracts - Society for Developmental Biology

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in the villi at E14. At E11, the major blood vessels, circumferentially covering the midgut, are first detected. The visceral
smooth muscle layer was first apparent at E6, both circular and longitudinal layers at E12, and subepithelial myofibroblasts
were identified in the villi at E14. Taken together, these dataprovide a comprehensive timeline of intestinal development.
Developmental processes not normally correlated may have both a temporal and morphological relationship. This timeline
will benefit both researchers examining intestinal development and clinicians studying congenital syndromes that may
originate from a combination of disrupted developmental processes.
Program/Abstract # 167
Identification of a novel developmental mechanism in the generation of mesothelia
Winters, Nichelle I.; Thomason, Rebecca; Bader, David, Vanderbilt University, Nashville, United States
Mesothelial cells form the surface layer of all coelomic structures and are essential to organ function. During development,
these cells undergo an epithelial to mesenchymal transition (EMT) to provide the precursors for the vasculature and
stromal cells to all coelomic organs investigated to date. Furthermore, in the adult, mesothelial cells stimulated by disease
or injury retain the ability to undergo EMT to generate fibroblasts and vascular smooth muscle cells mimicking their
developmental behavior. Despite the broad contribution of this cell type to developing organs and adult disease, our
current understanding of the genesis of this cell type is confined to a single organ, the heart, in which an exogenous
population of cells, the proepicardium, migrates to and over the myocardium to give rise to the cardiac mesothelium and
coronary vasculature. It is unknown whether this pattern of development is specific to the heart or applies broadly to other
coelomic organs. Using two independent long term lineage tracing studies, we demonstrate that mesothelial progenitors of
the intestine are intrinsic to the gut tube anlage. Furthermore, a novel chick-quail chimera model of gut morphogenesis
reveals these mesothelial progenitors are broadly distributed throughout the gut primordium and are not derived from a
localized and exogenous proepicardium-like source of cells. These data demonstrate an intrinsic origin of mesothelial cells
to a coelomic organ and provide a novel mechanism for the generation of mesothelial cells.
Program/Abstract # 168
Lasp regulates actin filament dynamics in Drosophila myofibril assembly.
Fernandes, Isabelle; Schoeck, Frieder, McGill University, Montreal, Canada
The actin cytoskeleton plays a key role in a number of motile and morphogenetic processes. The coordinated assembly and
disassembly of actin filaments promotes cell shape changes, mediates motility, contractility, and many other processes. In
each case, actin dynamics is finely regulated by a large number of actin-binding proteins (ABPs) that control actin filament
polymerization, nucleation and crosslinking. One group of ABPs is the nebulin family. To date, this family comprises 5
members, each containing from 2 to 185 actin-binding nebulin repeats. In our previous work, we showed that Lasp is the
single member of this family in Drosophila. Lasp has an N-terminal LIM domain, two nebulin repeats, and a C-terminal
SH3 domain. Lasp null mutants are homozygous viable, but male sterile. The stem cell niche is not properly anchor and
actin cone migration is impaired, resulting in failure of spermatid individualization. Recently, we discovered that Lasp also
functions in myofibril assembly. In Lasp mutants, sarcomere length is reduced and muscle contractility is weaker than in
wild type flies. These results are consistent with a function of nebulin family proteins as scaffolding and actin filament
organizing proteins. Using a double-tagged Lasp, I performed a pull down assay to identify interacting partners. As
expected Lasp binds muscle-specific actin isoforms. More surprisingly, most of the isolated proteins are components of
thick filaments, suggesting new functions for Lasp. We will report which domain of Lasp regulates actin dynamics, protein
interactions and proper localization in sarcomere assembly. By deciphering Lasp function in both Z-disc and A-band, we
will obtain further insights into the mechanism of myogenesis.
Program/Abstract # 169
Muscle type-specific expression and function of Zasp52 isoforms in Drosophila
Schoeck, Frieder; Katzemich, Anja; Fernandes, Isabelle, McGill University, Montreal, Canada
Zasp52 is a member of the PDZ-LIM domain protein family in Drosophila, which comprises Enigma, ENH, ZASP, Alp,
CLP36, RIL, and Mystique in vertebrates. Drosophila Zasp52 colocalizes with integrins at myotendinous junctions and
with α-actinin at Z-discs,and is required for muscle attachment as well as Z-disc assembly and maintenance. Here we
document thirteen Zasp52 splice variants giving rise to six different LIM domains. We demonstrate stage-and tissuespecific
expression in different muscle types for Zasp52 isoforms encoding different LIM domains. In particular, LIM1b is
expressed only in heart muscle and certain somatic muscles, implying muscle-specific functions in Z-disc assembly or
maintenance. We will present the phenotype of certain isoform-specific RNAi knockdowns.