Functions of LKB1 in neural crest development: The story unfolds.

Neural crest cells (NCCs) are highly motile, multipotent, embryonic cells that delaminate from the dorsal edges of the neural tube. NCCs follow stereotypical long-range migratory pathways to reach target organs during development, where they give rise to multiple derivatives. The identification of reservoirs of neural crest stem cells that persist to adulthood has recently aroused renewed interest in the biology of NCCs.

LKB1 specifies neural crest cell fates through pyruvate-alanine cycling.

Metabolic processes underlying the development of the neural crest, an embryonic population of multipotent migratory cells, are poorly understood. Here, we report that conditional ablation of the tumor suppressor kinase in mouse neural crest stem cells led to intestinal pseudo-obstruction and hind limb paralysis. This phenotype originated from a postnatal degeneration of the enteric nervous ganglia and from a defective differentiation of Schwann cells.

[Even the Warburg effect can be oxidized: metabolic cooperation and tumor development].

During tumor development, malignant cells rewire their metabolism to meet the biosynthetic needs required to increase their biomass and to overcome their microenvironment constraints. The sustained activation of aerobic glycolysis, also called Warburg effect, is one of these adaptative mechanisms. The progresses in this area of research have revealed the flexibility of cancer cells that alternate between glycolytic and oxidative metabolism to cope with their conditions of development while sharing their energetic resources.

LKB1 signaling in cephalic neural crest cells is essential for vertebrate head development.

Head development in vertebrates proceeds through a series of elaborate patterning mechanisms and cell-cell interactions involving cephalic neural crest cells (CNCC). These cells undergo extensive migration along stereotypical paths after their separation from the dorsal margins of the neural tube and they give rise to most of the craniofacial skeleton. Here, we report that the silencing of the LKB1 tumor suppressor affects the delamination of pre-migratory CNCC from the neural primordium as well as their polarization and survival, thus resulting in severe facial and brain defects.

The RNA-binding protein Mex3b regulates the spatial organization of the Rap1 pathway.

The four related mammalian MEX-3 RNA-binding proteins are evolutionarily conserved molecules for which the in vivo functions have not yet been fully characterized. Here, we report that male mice deficient for the gene encoding Mex3b are subfertile. Seminiferous tubules of Mex3b-deficient mice are obstructed as a consequence of the disrupted phagocytic capacity of somatic Sertoli cells.

Patched dependence receptor triggers apoptosis through ubiquitination of caspase-9.

Patched (Ptc), the main receptor for Sonic Hedgehog, is a tumor suppressor. Ptc has been shown to be a dependence receptor, and as such triggers apoptosis in the absence of its ligand. This apoptosis induction occurs through the recruitment by the Ptc intracellular domain of a caspase-activating complex, which includes the adaptor proteins DRAL and TUCAN, and the apical caspase-9.

Dependence receptors: mechanisms of an announced death.

Dependence receptors form a family of functionally related receptors which are all able to induce two completely opposite intracellular signals depending on the availability of their ligand. Indeed, in its presence, they mediate a positive, classical signal transduction of survival, differentiation or migration but without it, they trigger a negative signal which leads to cell death. The molecular mechanisms involved in triggering cell death in the absence of ligand are starting to be unravelled: dependence receptors are recruited at well-defined domains at the plasma membrane, they trigger cell death through a monomeric form, they are cleaved by caspases and they recruit a caspase activating complex.

Alix is involved in caspase 9 activation during calcium-induced apoptosis.

The cytoplasmic protein Alix/AIP1 (ALG-2 interacting protein X) is involved in cell death through mechanisms which remain unclear but require its binding partner ALG-2 (apoptosis-linked gene-2). The latter was defined as a regulator of calcium-induced apoptosis following endoplasmic reticulum (ER) stress. We show here that Alix is also a critical component of caspase 9 activation and apoptosis triggered by calcium.

Interfering with multimerization of netrin-1 receptors triggers tumor cell death.

Netrin-1 was recently proposed to control tumorigenesis by inhibiting apoptosis induced by the dependence receptors DCC (Deleted in colorectal cancer) and UNC5H. Although the loss of these dependence receptors' expression has been described as a selective advantage for tumor growth and progression in numerous cancers, recent observations have shown that some tumors may use an alternative strategy to block dependence receptor-induced programmed cell death: the autocrine expression of netrin-1. This alternative strategy has been observed in a large fraction of aggressive breast cancers, neuroblastoma, pancreatic adenocarcinoma, and lung cancer.

The Patched dependence receptor triggers apoptosis through a DRAL-caspase-9 complex.

Sonic hedgehog (Shh) and its main receptor, Patched (Ptc), are implicated in both neural development and tumorigenesis. Besides its classic morphogenic activity, Shh is also a survival factor. Along this line, Ptc has been shown to function as a dependence receptor; it induces apoptosis in the absence of Shh, whereas its pro-apoptotic activity is blocked in the presence of Shh.

Morphogens and cell survival during development.

The notion of "morphogens" is an important one in developmental biology. By definition, a morphogen is a molecule that emanates from a specific set of cells that is present in a concentration gradient and that specifies the fate of each cell along this gradient. The strongest candidate morphogens are members of the transforming growth factor-beta (TGF-beta), Hedgehog (Hh), and Wnt families.

Dependence receptors: between life and death.

The recently described family of dependence receptors is a new family of functionally related receptors. These proteins have little sequence similarity but display the common feature of inducing two completely opposite intracellular signals depending on ligand availability: in the presence of ligand, these receptors transduce a positive signal leading to survival, differentiation or migration, while in the absence of ligand, the receptors initiate or amplify a negative signal for apoptosis. Thus, cells that express these proteins manifest a state of dependence on their respective ligands.

Inhibition of neuroepithelial patched-induced apoptosis by sonic hedgehog.

During early development in vertebrates, Sonic hedgehog (Shh) is produced by the notochord and the floor plate. A ventrodorsal gradient of Shh directs ventrodorsal patterning of the neural tube. However, Shh is also required for the survival of neuroepithelial cells.

Germline transformation of the silkworm Bombyx mori L. using a piggyBac transposon-derived vector.

We have developed a system for stable germline transformation in the silkworm Bombyx mori L. using piggyBac, a transposon discovered in the lepidopteran Trichoplusia ni. The transformation constructs consist of the piggyBac inverted terminal repeats flanking a fusion of the B.