Convergence and Extension Movements During Vertebrate Gastrulation,

Chunyue Yin, Brian Ciruna, Lilianna Solnica-Krezel

In: Thomas Lecuit, Editor(s), Current Topics in Developmental Biology, Academic Press, 2009, Volume 89, Pages 163-192, DOI: 10.1016/S0070-2153(09)89007-8.

During vertebrate gastrulation, coordinated cell movements shape the basic body plan. Key components of gastrulation are convergence and extension (C&E) movements, which narrow and lengthen the embryonic tissues, respectively. The rates of C&E movements differ significantly according to the position and the stage of gastrulation. Here, we review the distinct cellular behaviors that define the spatial and temporal patterns of C&E movements, with the special emphasis on zebrafish. We also summarize the molecular regulation of these cellular behaviors and the interplay between different signaling pathways that drive C&E. Finally, to ensure efficient C&E movements, cells must achieve mediolaterally-elongated cell morphology and polarize motile protrusions. We discuss the recent discoveries on the molecular and cellular mechanisms by which the mediolateral cell polarity is established.

CCN3 – A key regulator of the hematopoietic compartment.

McCallum L, Irvine AE.
Blood Rev. 2008 Aug 25.

CCN3, a founding member of the CCN family of growth regulators, was linked with hematology in 2003(1) when it was detected in human serum. CCN3 is expressed and secreted by hematopoietic progenitor cells in normal bone marrow. CCN3 acts through the core stem cell signalling pathways including Notch and Bone Morphogenic Protein, connecting CCN3 with the modulation of self-renewal and maturation of a number of cell lineages including hematopoietic, osteogenic and chondrogenic. CCN3 expression is disrupted in Chronic Myeloid Leukemia as a consequence of the BCR-ABL oncogene and allows the leukemic clone to evade growth regulation. In contrast, naïve cord blood progenitors undergo enhanced clonal expansion in response to CCN3. Altered CCN3 expression is associated with numerous solid tumors including glioblastoma, melanoma, adrenocortical tumours, prostate cancer and bone malignancies including osteosarcoma. Mature CCN3 protein has five distinct modules and truncated protein variants with altered function are found in many cancers. Regulation by CCN3 is therefore cell type and isoform specific. CCN3 has emerged as a key player in stem cell regulation, hematopoiesis and a crucial component within the bone marrow microenvironment

Visualization of Cartilage Formation: Insight into Cellular Properties of Skeletal Progenitors and Chondrodysplasia Syndromes

Visualization of Cartilage Formation: Insight into Cellular Properties of Skeletal Progenitors and Chondrodysplasia Syndromes

Maria Barna and Lee Niswander

Developmental Cell, Volume 12, Issue 6, 5 June 2007, Pages 931-941

The cellular events underlying skeletal morphogenesis and the formation of cartilage templates are largely unknown. We generated an imaging system to dynamically visualize limb mesenchymal cells undergoing successive phases in cartilage formation and to delineate the cellular function of key regulators of chondrogenesis found mutated in chondrodysplasia syndromes. We uncovered an unsuspected role for Sox9 in control of cell morphology, independent from its major downstream target ColIIa, critically required for the mesenchyme-to-chondrocyte transition. In contrast, Bmp signaling regulates a cellular program we term “compaction” in which mesenchymal cells acquire a cohesive cell behavior required to delineate the boundaries and size of cartilage elements. Moreover, we visualized labeled progenitor cells from different regions of the limb bud and identified unique cellular properties that may direct their contribution toward specific skeletal elements such as the humerus or digits. These findings shed light on the cellular basis for chondrodysplasia syndromes and formation of the vertebrate skeleton.

Cessation of gastrulation is mediated by suppression of epithelial-mesenchymal transition at the ventral ectodermal ridge

Sho Ohta, Kentaro Suzuki, Katsuro Tachibana, Hideaki Tanaka and Gen Yamada

Development 134, 4315-4324(2007) doi:10.1242/dev.008151

In the gastrula stage embryo, the epiblast migratestoward the primitive streak and ingressesthrough the primitive groove. Subsequently, the ingressing epiblast cells undergo epithelial-mesenchymal transition (EMT) and differentiate into the definitive endoderm and mesoderm during gastrulation. However, the developmental mechanisms at the end of gastrulation have not yet been elucidated. Histological and genetic analyses of the ventral ectodermal ridge (VER), a derivative of the primitive streak, were performed using chick and mouse embryos. The analyses showed a continued cell movement resembling gastrulation associated with EMT during the early tailbud stage of both embryos. Such gastrulation-like cell movement was gradually attenuated by the absence of EMT during tail development. The kinetics of the expression pattern of noggin (Nog) and basal membrane degradation adjacent to the chick and the mouse VER indicated a correlation between the temporal and/or spatial expression of Nog and the presence of EMT in the VER. Furthermore, Nog overexpression suppressed EMT and arrested ingressive cell movement in the chick VER. Mice mutant in noggin displayed dysregulation of EMT with continued ingressive cell movement. These indicate that the inhibition of Bmp signaling by temporal and/or spatial Nog expression suppresses EMT and leads to the cessation of the ingressive cell movement from the VER at the end of gastrulation.