Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

https://www.um.es/biomybiotec/web/Seminarios/2010/papers/Cano_2.pdf

Epithelial-Mesenchymal Transitions in Development and Disease

Without epithelial–mesenchymal transitions, in which polarized epithelial cells are converted into motile cells, multicellular organisms would be incapable of getting past the blastula stage of embryonic development. However, this important developmental programme has a more sinister role in tumour progression. Epithelial–mesenchymal transition provides a new basis for understanding the progression of carcinoma towards dedifferentiated and more malignant states.

Epithelial–mesenchymal transitions in tumour progression

Rapid progress has been made in the understanding of the molecular interactions that result in cell adhesion. Many adhesive proteins present in extracellular matrices and in the blood contain the tripeptide arginine-glycine-aspartic acid (RGD) as their cell recognition site. These proteins include fibronectin, vitronectin, osteopontin, collagens, thrombospondin, fibrinogen, and von Willebrand factor. The RGD sequences of each of the adhesive proteins are recognized by at least one member of a family of structurally related receptors, integrins, which are heterodimeric proteins with two membrane-spanning subunits. Some of these receptors bind to the RGD sequence of a single adhesion protein only, whereas others recognize groups of them. The conformation of the RGD sequence in the individual proteins may be critical to this recognition specificity. On the cytoplasmic side of the plasma membrane, the receptors connect the extracellular matrix to the cytoskeleton. More than ten proved or suspected RGD-containing adhesion-promoting proteins have already been identified, and the integrin family includes at least as many receptors recognizing these proteins. Together, the adhesion proteins and their receptors constitute a versatile recognition system providing cells with anchorage, traction for migration, and signals for polarity, position, differentiation, and possibly growth.

https://science.sciencemag.org/content/sci/238/4826/491.full.pdf

New perspectives in cell adhesion : RGD and integrins

Integrins: a family of cell surface receptors.

twist and snail are members of the helix-loop-helix and zinc-finger protein families, respectively, and determine the development of the mesoderm in Drosophila. This paper analyzes their role in mesoderm development by examining how they affect the expression of downstream genes. twist and snail act by regulating gene expression in the mesoderm and in neighboring regions, and have distinct roles in this process. snail prevents expression in the mesoderm of genes that are destined to be active only in more lateral or dorsal regions. twist is required for the activation of downstream mesodermal genes. twist is also required for the full expression of snail and for the maintenance of its own expression. Only the absence of both twist and snail results in the complete loss of all mesodermal characteristics.

/pdf/twist-and-snail-as-positive-and-negative-regulators-during-33baxdlsn8.pdf

twist and snail as positive and negative regulators during Drosophila mesoderm development.

The first morphogenetic movement during Drosophila development is the invagination of the mesoderm, an event that folds a one-layered epithelium into a multilayered structure. In this paper, we describe the shape changes and behaviour of the cells participating in this process and show how mutations that change cell fate affect this behaviour. We divide the formation of the mesodermal germ layer into two phases. During the first phase, the ventral epithelium folds into a tube by a series of concerted cell shape changes (ventral furrow formation). Based on the behaviour of cells in this phase, we conclude that the prospective mesoderm is not a homogeneous cell population, but consists of two subpopulations. Each subpopulation goes through a distinctive sequence of specific cell shape changes which together mediate the invagination of the ventral furrow. In the second phase, the invaginated tube of mesoderm loses its epithelial character, the mesoderm cells disperse, divide and then spread out along the ectoderm to form a single cell layer. To test how ventral furrow formation depends on cell fates in the mesoderm and in neighbouring cells we alter these fates genetically using maternal and zygotic mutations. These experiments show that some of the aspects of cell behaviour specific for ventral furrow cells are part of an autonomous differentiation programme. The force driving the invagination is generated within the region of the ventral furrow, with the lateral and dorsal cell populations contributing little or none of the force. Two known zygotic genes that are required for the formation of the mesoderm, twist and snail, are expressed in ventral furrow cells, and the correct execution of cell shape changes in the mesoderm depends on both. Finally, we show that the region where the ventral furrow forms is determined by the expression of mesoderm-specific genes, and not by mechanical or other epigenetic properties of the egg.

Cell shape changes during gastrulation in Drosophila

https://www.cell.com/cell/pdf/S0092-8674(00)80482-1.pdf

The Rho GTPase and a putative RhoGEF mediate a signaling pathway for the cell shape changes in Drosophila gastrulation.

The zebrafish has become a widely used model to study disease resistance and immunity. Although the genes encoding many components of immune signaling pathways have been found in teleost fish, it is not clear whether all components are present or whether the complexity of the signaling mechanisms employed by mammals is similar in fish. We searched the genomes of the zebrafish Danio rerio and two pufferfish for genes encoding components of the Toll-like receptor and interferon signaling pathways, the NLR (NACHT-domain and leucine rich repeat containing) protein family, and related proteins. We find that most of the components known in mammals are also present in fish, with clearly recognizable orthologous relationships. The class II cytokines and their receptors have diverged extensively, obscuring orthologies, but the number of receptors is similar in all species analyzed. In the family of the NLR proteins, the canonical members are conserved. We also found a conserved NACHT-domain protein with WD40 repeats that had previously not been described in mammals. Additionally, we have identified in each of the three fish a large species-specific subgroup of NLR proteins that contain a novel amino-terminal domain that is not found in mammalian genomes. The main innate immune signaling pathways are conserved in mammals and teleost fish. Whereas the components that act downstream of the receptors are highly conserved, with orthologous sets of genes in mammals and teleosts, components that are known or assumed to interact with pathogens are more divergent and have undergone lineage-specific expansions.

/pdf/conservation-and-divergence-of-gene-families-encoding-4dfwxtjqap.pdf

Conservation and divergence of gene families encoding components of innate immune response systems in zebrafish

A hallmark of epithelial invagination is the constriction of cells on their apical sides. During Drosophila gastrulation, apical constrictions under the control of the transcription factor Twist lead to the invagination of the mesoderm. Twist-controlled G protein signaling is involved in mediating the invagination but is not sufficient to account for the full activity of Twist. We identified a Twist target, the transmembrane protein T48, which acts in conjunction with G protein signaling to orchestrate shape changes. Together with G protein signaling, T48 recruits adherens junctions and the cytoskeletal regulator RhoGEF2 to the sites of apical constriction, ensuring rapid and intense changes in cell shape.

http://science.sciencemag.org/content/sci/315/5810/384.full.pdf

Maria Leptin

Papers

twist and snail as positive and negative regulators during Drosophila mesoderm development.

Cell shape changes during gastrulation in Drosophila

The Rho GTPase and a putative RhoGEF mediate a signaling pathway for the cell shape changes in Drosophila gastrulation.

Conservation and divergence of gene families encoding components of innate immune response systems in zebrafish

Control of Drosophila Gastrulation by Apical Localization of Adherens Junctions and RhoGEF2