Congress Abstracts - Society for Developmental Biology

Program/Abstract # 230
The Drosophila Z-disc protein Z(210) is an adult muscle isoform of Zasp52, which is required for normal myofibril
organization in indirect flight muscles
Chechenova, Maria B.; Bryantsev, Anton; Cripps, Richard (The University of New Mexico, USA)
The Z-disc is a critical anchoring point for thin filaments as they slide during muscle contraction, therefore identifying components of
the Z-disc is critical for fully comprehending how myofibrils assemble and function. In the adult Drosophila musculature, the fibrillar
indirect flight muscles (IFMs) accumulate several high-molecular weight Z-disc proteins, the identities of which have to date been
unknown. Here we use mass spectrometry and gene specific knockdown studies to identify one of these proteins, previously known as
Z(210), as an isoform of the Z-disc protein Zasp52. The Zasp52 primary transcript is extensively alternatively spliced, and we describe
its IFM-specific isoform. This isoform is detected in adult flies only, and not found in larvae. Finally, we demonstrate that Zasp52 in
the fibrillar muscles is required for proper localization of another structural component of Z-discs, alpha-actinin, and for normal
sarcomere structure, but not sufficient for distribution of some other structural sarcomere proteins, such as MLP84B and Sls. These
studies expand our knowledge of Zasp proteins and their functions in muscle. Given the role of Zasp proteins in mammalian muscle
development and disease, our results have broader relevance to muscle biology.
Program/Abstract # 231
Whole or Hole? Development of a Functional Diaphragm
Merrell, Allyson; Kardon, Gabrielle (University of Utah, USA)
The diaphragm is functionally the most important skeletal muscle in mammals, as it is essential for respiration. Strikingly, defects in
diaphragm development are common birth defects (1:3000 births) that cause congenital diaphragmatic hernias (CDH) and result in
high neonatal mortality and long-term morbidity. Despite its functional importance and the frequency and severity of CDH, our
understanding of the embryonic origins, cell-cell interactions, and genetic mechanisms underlying diaphragm development normally
and during herniation is limited. Using mouse genetic reagents, we have visualized for the first time the morphogenesis of the
diaphragm’s muscle, muscle connective tissue, and central tendon by identifying and genetically labeling the developmental sources
of these tissues. We find that the morphogenesis of muscle and its connective tissue is tightly linked spatially and temporally. In
addition, because the connective tissue can develop normally in the absence of muscle, the connective tissue is likely to be the driver
of diaphragm morphogenesis. Furthermore, demonstrating the critical role of the connective tissue, we show via conditional
mutagenesis that genetic defects in the connective tissue (and not the muscle) are the cause, with 100% penetrance, of CDH. By
genetically labeling and visualizing the mutant connective tissue fibroblasts, we show that connective tissue is present throughout the
diaphragm, but myogenic cells are locally devoid in the herniated regions. The presence of mechanically weak amuscular regions
juxtaposed to stronger, muscularized regions allows liver to herniate through the weaker regions. Thus we show that the muscle
connective tissue is critical for normal diaphragm development and CDH.
Program/Abstract # 232
Rab11 plays an indispensable role in the differentiation and development of the adult muscles in Drosophila
Singh, Divya; Roy, Jagat Kumar (Banaras Hindu University, India)
Rab11, an evolutionary conserved, ubiquitously expressed subfamily of small monomeric GTPase has been known to regulate diverse
cellular and developmental events, by regulating the exocytic and transcytotic events inside the cell. Our studies show that Rab11
regulates Drosophila adult myogenesis by controlling proliferation and differentiation of the Adult muscle precursors (AMPs).
Blocking Rab11 in the AMPs, which fuse to form the Indirect Flight Muscles (IFMs) of the fly results in rendering the flies
completely flightless and non-viable. The IFMs comprising of the differentially patterned dorsal longitudinal muscles and dorsal
ventral muscle are affected to different extents. Abrogating normal Rab11 function or knocking down its function results in severely
disrupted IFM structure. DLMs forming from larval templates are reduced in number along with a significant reduction in their fibre
size. On the other hand, the de novo developing DVMs are frequently absent. The DLMs in Rab11 hypomorphs are highly reduced,
showing as a small constricted mass in one half of the thorax. Furthermore, we found that, Rab11 function is essential for the growth
of these muscles during later half of adult myogenesis, as on altering Rab11 in the IFMs results in degenerated muscles and broken
fibres. Finally, we show that loss of Rab11 activity in the AMPs result in acquisition of migratory characteristic of myoblast as they
show cellular protrusion at their polar ends accompanied with loss of cell-cell contacts. We surmise a functional requirement of Rab11
at early stages of muscle development and our data provide the first line of evidence of a trafficking protein playing an indispensable
role in regulating the adult muscle development.
Program/Abstract # 233
The gene regulation in skeletal myogenesis in medaka, Oryzias latipes
Tani, Saori, (USA), Kusakabe, Rie; Inoue, Kunio (Kobe, Japan)
We have analyzed microRNA (miR) expression and function in medaka (Oryzias latipes), a small fresh water fish. miRs are noncoding
RNA molecules of 22 nt long, which silence the target mRNAs by imperfect base-pairing with the 3’UTR. In mammals, miR-
1, -206 and -133 are involved in myoblast proliferation and differentiation. We identified miR-1, miR-206 and miR-133 genes in the
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