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Frontiers in Biology

Front Biol    2012, Vol. 7 Issue (1) : 73-82
Drosophila embryo syncytial blastoderm cellular architecture and morphogen gradient dynamics: Is there a correlation?
Indian Institute of Science, Education and Research, Biology, 301, Central Tower, Sai Trinity Bldg, Pashan, Pune 411021, India
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During embryo development in many metazoan animals, the first differentiated cell type to form is an epithelial cell. This epithelial layer is modified by developmental cues of body axes formation to give rise to various tissues. The cells that arise are mesenchymal in nature and are a source of other tissue types. This epithelial to mesenchymal transition is used for tissue type formation and also seen in diseases such as cancer. Here we discuss recent findings on the cellular architecture formation in the Drosophila embryo and how it affects the developmental program of body axes formation. In particular these studies suggest the presence of compartments around each nucleus in a common syncytium. Despite the absence of plasma membrane boundaries, each nucleus not only has its own endoplasmic reticulum and Golgi complex but also its own compartmentalized plasma membrane domain above it. This architecture is potentially essential for morphogen gradient restriction in the syncytial Drosophila embryo. We discuss various properties of the dorso-ventral and the antero-posterior morphogen gradients in the Drosophila syncytium, which are likely to depend on the syncytial architecture of the embryo.

Keywords morphogen gradient      Drosophila      syncytium      embryo      cellular architecture     
Corresponding Author(s): RIKHY Richa,   
Issue Date: 01 February 2012
 Cite this article:   
Aparna SHERLEKAR,Richa RIKHY. Drosophila embryo syncytial blastoderm cellular architecture and morphogen gradient dynamics: Is there a correlation?[J]. Front Biol, 2012, 7(1): 73-82.
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Fig.1  The cellular architecture in the syncytial embryo during interphase of the nuclear cycles 11-13. The centrosomes are present apically. These form microtubules in the vertical direction. The endoplasmic reticulum and the Golgi complex are partitioned to each nucleus and show compartmentalization of diffusion around each nucleus. The actin cytoskeleton is present as caps beneath apical plasma membrane, which is rich in microvilli. The lateral plasma membrane, which surrounds each nucleus only partially during interphase of the syncytial cycle, contains specific transmembrane proteins such as Tl, junctional proteins such as Cadherin and Patj, cytoskeletal-remodeling proteins such as Anillin and Peanut and endocytosis proteins such as Dynamin and Clathrin (not drawn to scale).
Fig.2  Bicoid (Bcd) gradient in the syncytium. The mRNA and the Bcd protein form a gradient across the syncytial nuclei in the anterior (A). The Staufen protein is required for anchoring the mRNA at the anterior of the embryo. The Bcd protein is formed from translation of the mRNA and enters the nucleus where it activates specific downstream gene expression responsible for determining the anterior end of the embryo (B) (not drawn to scale).
Fig.3  MAP kinase (MAPK) gradient in the syncytium. The MAPK gradient is formed on the anterior and the posterior by the activation of the Torso (Tor) receptor (A). The Tor receptor gets activated by processing of the Tor-like ligand in the perivitelline space. The Tor receptor is present all over the plasma membrane and is endocytosed and degraded in lysosomes after activation (B) (not drawn to scale).
Fig.4  Dorsal (Dl) gradient in the syncytium. The Dl gradient in the syncytium is formed in response to activation of Toll (Tl) receptor by Sp?ztle (Spz) (A). The Tl receptor is activated by cleaved Spz locally formed in the perivitelline space on the ventral side. The activated Tl receptor is endocytosed and has been shown to signal from Rab5 positive early endosomes (B) (not drawn to scale).
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