A permissive role of Notch in maintaining the DV affinity boundary of the Drosophila wing

AbstractCell affinities can contribute to organizing cells into tissues and organs. Drosophila limbs and the vertebrate central nervous system are subdivided into adjacent populations that do not mix. These cell populations are called compartments. Cell interactions mediated by receptor Notch have been implicated in the specification of compartment boundaries. However, the contribution of Notch in this process remains controversial. The instructive role of Notch and the transcriptional requirement of the pathway have been questioned in the last few years. Due to its central role in making developmental boundaries in vertebrates and invertebrates, we have reevaluated the contribution of Notch and its signaling pathway in the maintenance of an affinity difference between dorsal (D) and ventral (V) compartments in the Drosophila wing. Here we present evidence that unrestricted, low levels of Notch are sufficient for the formation of a stable DV affinity boundary. Cleavage of the Notch protein, release of the intracellular domain and a transcriptional function of Notch via the Suppressor of Hairless transcription factor are required and sufficient in this process. Our data support a permissive role of Notch in maintaining the DV affinity boundary. This contrasts with the instructive role of Notch in executing the organizing activity of the DV boundary

Calderón encodes an organic cation transporter of the major facilitator superfamily required for cell growth and proliferation of Drosophila tissues

The adaptation of growth in response to dietary changes is essential for the normal development of all organisms. The insulin receptor (InR) signalling pathway controls growth and metabolism in response to nutrient availability. The elements of this pathway have been described, although little is known about the downstream elements regulated by this cascade. We identified calderón, a gene that encodes a protein with highest homology with organic cation transporters of the major facilitator superfamily, as a new transcriptional target of the InR pathway. These transporters are believed to function mainly in the uptake of sugars, as well as other organic metabolites. Genetic experiments demonstrate that calderón is required cell autonomously and downstream of the InR pathway for normal growth and proliferation of larval tissues. Our results indicate that growth of imaginal cells may be modulated by two distinct, but coordinated, nutrient-sensing mechanisms: one cell-autonomous and the other humoral.Dirección General de Investigación Científica y Técnica (BFU2004-00167/BMC) and by EU research contract LSHM-CP-2003-503330 (APOPIS). Work in G.M.’s laboratory is funded by a grant from the Dirección General de Investigación Científica y Técnica (BMC2002-01959)Peer Reviewe

JAK/STAT controls organ size and fate specification by regulating morphogen production and signalling

A stable pool of morphogen-producing cells is critical for the development of any organ or tissue. Here we present evidence that JAK/STAT signalling in the Drosophila wing promotes the cycling and survival of Hedgehog-producing cells, thereby allowing the stable localization of the nearby BMP/Dpp-organizing centre in the developing wing appendage. We identify the inhibitor of apoptosis dIAP1 and Cyclin A as two critical genes regulated by JAK/STAT and contributing to the growth of the Hedgehog-expressing cell population. We also unravel an early role of JAK/STAT in guaranteeing Wingless-mediated appendage specification, and a later one in restricting the Dpp-organizing activity to the appendage itself. These results unveil a fundamental role of the conserved JAK/STAT pathway in limb specification and growth by regulating morphogen production and signalling, and a function of pro-survival cues and mitogenic signals in the regulation of the pool of morphogen-producing cells in a developing organ

The LRR Proteins Capricious and Tartan Mediate Cell Interactions during DV Boundary Formation in the Drosophila Wing

AbstractMechanisms to segregate cell populations play important roles in tissue patterning during animal development. Rhombomeres and compartments in the ectoderm and imaginal discs of Drosophila are examples in which initially homogenous populations of cells come to be separated by boundaries of lineage restriction. Boundary formation depends in part on signaling between the distinctly specified cell populations that comprise compartments and in part on formation of affinity boundaries that prevent intermingling of these cell populations. Here, we present evidence that two transmembrane proteins with leucine-rich repeats, known as Capricious and Tartan, contribute to formation of the affinity boundary between dorsal and ventral compartments during Drosophila wing development

A dp53-Dependent Mechanism Involved in Coordinating Tissue Growth in Drosophila

A study in the Drosophila wing suggests a crucial role of p53 in the coordination of growth between adjacent cell populations to maintain organ proportions and shape. Coordination of growth between and within organs contributes to the generation of well-proportioned organs and functionally integrated adults. The mechanisms that help to coordinate the growth between different organs start to be unravelled. However, whether an organ is able to respond in a coordinated manner to local variations in growth caused by developmental or environmental stress and the nature of the underlying molecular mechanisms that contribute to generating well-proportioned adult organs under these circumstances remain largely unknown. By reducing the growth rates of defined territories in the developing wing primordium of Drosophila, we present evidence that the tissue responds as a whole and the adjacent cell populations decrease their growth and proliferation rates. This non-autonomous response occurs independently of where growth is affected, and it is functional all throughout development and contributes to generate well-proportioned adult structures. Strikingly, we underscore a central role of Drosophila p53 (dp53) and the apoptotic machinery in these processes. While activation of dp53 in the growth-depleted territory mediates the non-autonomous regulation of growth and proliferation rates, effector caspases have a unique role, downstream of dp53, in reducing proliferation rates in adjacent cell populations. These new findings indicate the existence of a stress response mechanism involved in the coordination of tissue growth between adjacent cell populations and that tissue size and cell cycle proliferation can be uncoupled and are independently and non-autonomously regulated by dp53. The coordination of growth within and between organs contributes to the generation of functionally integrated structures and well-proportioned animals and plants. Though these issues have fascinated biologists for centuries, the responsible molecular mechanisms remain largely uncharacterized. In this work, we have used the Drosophila wing primordium to show that adjacent cell populations grow and proliferate in a coordinated manner. By reducing growth rates in specific territories within the developing wing, we showed that the tissue responds as a whole and that in adjacent cell populations the growth and cell cycle rates are concomitantly reduced, thus maintaining tissue proportions and normal wing shape. Interestingly, we show that the Drosophila tumour suppressor protein dp53 and apoptotic machinery play a key role in coordinating this tissue-wide response. Both growth and proliferation rates are regulated in a coordinated and non-autonomous manner by the activity of dp53, whilst the apoptotic pathway has a specific and non-autonomous role in regulating cell proliferation rates. Our studies describe a novel mechanism for regulating tissue growth in developing organs that may ultimately be relevant for other processes involving coordination of growth, such as tissue renewal, regeneration, and cancer

Hematologic and serum chemistry values of the captive european wildcat

Hematologic and serum chemistry values were determined for 20 adult captive European wildcats (Felis silvestris) in Lleida (Catalonia, Spain). Seven wildcats (4 females and 3 males) were captured in the wild and 13 (4 females and 9 males) were born and raised in captivity. Samples were collected between September and December from 1993 to 1998. Blood was obtained by jugular venipuncture after administration of either ketamine and xylazine or ketamine and medetomidine. Females had significantly higher mean eosinophil counts, albumin concentration, (and A/G ratio) and lower mature neutrophil counts, although these differences were not clinically relevant. Results for many of the blood parameters fall within the reference range for domestic cats. Mean values for alanine aminotransferase, aspartate aminotransferase, creatine phosphokinase, and lactate dehydrogenase activities as well as blood urea nitrogen, glucose, and sodium concentrations were higher than the upper limit of the reference range for domestic cat

Embolización cartilaginosa en la aorta abdominal secundaria a una lesión arterioesclerótica en la aorta torácica en un perro

Se describe un caso de paraplegia aguda no progresiva en una perra adulta ocasionado por una embolización cartilaginosa en la aorta abdominal cuyo origen se encontraba en una lesión arterioesclerótica en la aorta torácica.

A Drosophila model of myeloproliferative neoplasm reveals a feed-forward loop in the JAK pathway mediated by p38 MAPK signalling

Myeloproliferative neoplasms (MPNs) of the Philadelphia-negative class comprise polycythaemia vera, essential thrombocythaemia and primary myelofibrosis (PMF). They are associated with aberrant numbers of myeloid lineage cells in the blood, and in the case of overt PMF, with development of myelofibrosis in the bone marrow and failure to produce normal blood cells. These diseases are usually caused by gain-of-function mutations in the kinase JAK2. Here, we use Drosophila to investigate the consequences of activation of the JAK2 orthologue in haematopoiesis. We have identified maturing haemocytes in the lymph gland, the major haematopoietic organ in the fly, as the cell population susceptible to induce hypertrophy upon targeted overexpression of JAK. We show that JAK activates a feed-forward loop, including the cytokine-like ligand Upd3 and its receptor, Domeless, which are required to induce lymph gland hypertrophy. Moreover, we present evidence that p38 MAPK signalling plays a key role in this process by inducing expression of the ligand Upd3. Interestingly, we also show that forced activation of the p38 MAPK pathway in maturing haemocytes suffices to generate hypertrophic organs and the appearance of melanotic tumours. Our results illustrate a novel pro-tumourigenic crosstalk between the p38 MAPK pathway and JAK signalling in a Drosophila model of MPNs. Based on the shared molecular mechanisms underlying MPNs in flies and humans, the interplay between Drosophila JAK and p38 signalling pathways unravelled in this work might have translational relevance for human MPNs