Drosophila haemocytes (blood cells) originate from a specialized haematopoietic organ-the lymph gland. Larval haematopoietic progenitors (prohaemocytes) give rise to three types of circulating haemocytes: plasmatocytes, crystal cells and lamellocytes. Lamellocytes, which are devoted to encapsulation of large foreign bodies, only differentiate in response to specific immune threats, such as parasitization by wasps. Here we show that a small cluster of signalling cells, termed the PSC (posterior signalling centre), controls the balance between multipotent prohaemocytes and differentiating haemocytes, and is necessary for the massive differentiation of lamellocytes that follows parasitization. Communication between the PSC and haematopoietic progenitors strictly depends on the PSC-restricted expression of Collier, the Drosophila orthologue of mammalian early B-cell factor. PSC cells act, in a non-cell-autonomous manner, to maintain JAK/STAT signalling activity in prohaemocytes, preventing their premature differentiation. Serrate-mediated Notch signalling from the PSC is required to maintain normal levels of col transcription. The key role of the PSC in controlling blood cell homeostasis is reminiscent of interactions between haematopoietic progenitors and their micro-environment in vertebrates, thus further highlighting the interest of Drosophila as a model system for studying the evolution of haematopoiesis and cellular innate immunity.

The Drosophila lymph gland (LG) is a model system for studying hematopoiesis and blood cell homeostasis. Here, we investigated the patterns of division and differentiation of pro-hemocytes in normal developmental conditions and response to wasp parasitism, by combining lineage analyses and molecular markers for each of the three hemocyte types. Our results show that the embryonic LG contains primordial hematopoietic cells which actively divide to give rise to a pool of pro-hemocytes. We found no evidence for the existence of bona fide stem cells and rather suggest that Drosophila pro-hemocytes are regulated as a group of cells, rather than individual stem cells. The fate-restriction of plasmatocyte and crystal cell progenitors occurs between the end of embryogenesis and the end of the first larval instar, while Notch activity is required for the differentiation of crystal cells in third instar larvae only. Upon parasitism, lamellocyte differentiation prevents crystal cell differentiation and lowers plasmatocyte production. We also found that a new population of intermediate progenitors appears at the onset of hemocyte differentiation and accounts for the increasing number of differentiated hemocytes in the third larval instar. These findings provide a new framework to identify parameters of developmental plasticity of the Drosophila lymph gland and hemocyte homeostasis in physiological conditions and in response to immunological cues.

Regulation of JAK/STAT signalling by a short, nonsignalling receptor in Drosophila modulates response to specific immune challenges such as parasitoid infestations.

Blood cell production in the Drosophila hematopoietic organ, the lymph gland, is controlled by intrinsic factors and extrinsic signals. Initial analysis of Collier/Early B Cell Factor function in the lymph gland revealed the role of the Posterior Signaling Center (PSC) in mounting a dedicated cellular immune response to wasp parasitism. Further, premature blood cell differentiation when PSC specification or signaling was impaired, led to assigning the PSC a role equivalent to the vertebrate hematopoietic niche. We report here that Collier is expressed in a core population of lymph gland progenitors and cell autonomously maintains this population. The PSC contributes to lymph gland homeostasis by regulating blood cell differentiation, rather than by maintaining core progenitors. In addition to PSC signaling, switching off Collier expression in progenitors is required for efficient immune response to parasitism. Our data show that two independent sites of Collier/Early B Cell Factor expression, hematopoietic progenitors and the PSC, achieve control of hematopoiesis.

Over the years, the fruit fly Drosophila melanogaster has become a major invertebrate model to study developmental and evolutionary aspects of both humoral and cellular aspects of innate immunity. Drosophila hematopoiesis which supplies three types of circulating hemocytes, occurs in two spatially and temporally distinct phases during development. The first embryonic phase is described in detail in accompanying reviews in this Int. J. Dev. Biol. Special Issue. The second phase takes place at the end of larval development in a specialised hematopoietic organ, termed the lymph gland. We review here recent studies on the ontogeny of the lymph gland, focusing on the formation and role of the Posterior Signalling Center which acts as a niche for hematopoietic progenitors. We then report recent progress in understanding the dedicated cellular immune response of Drosophila larvae against parasitization by Hymenopterae, a common threat for many Dipterae. This response involves the differentiation of lamellocytes, a cryptic cell fate, revealing the high degree of plasticity of Drosophila hematopoiesis. We end up by integrating studies in Drosophila within a more general picture of insect hematopoiesis and hemocyte homeostasis.

The angiomotin (Amot)–Yes-associated protein 1 (Yap1) complex plays a major role in regulating the inhibition of cell contact, cellular polarity, and cell growth in many cell types. However, the function of Amot and the Hippo pathway transcription coactivator Yap1 in the central nervous system remains unclear. We found that Amot is a critical mediator of dendritic morphogenesis in cultured hippocampal cells and Purkinje cells in the brain. Amot function in developing neurons depends on interactions with Yap1, which is also indispensable for dendrite growth and arborization in vitro. The conditional deletion of Amot and Yap1 in neurons led to a decrease in the complexity of Purkinje cell dendritic trees, abnormal cerebellar morphology, and impairments in motor coordination. Our results indicate that the function of Amot and Yap1 in dendrite growth does not rely on interactions with TEA domain (TEAD) transcription factors or the expression of Hippo pathway–dependent genes. Instead, Amot and Yap1 regulate dendrite development by affecting the phosphorylation of S6 kinase and its target S6 ribosomal protein.

SUMMARYIn the past, segments were defined by landmarks such as muscle attachments, notably by Snodgrass, the king of insect anatomists. Here, we show how an objective definition of a segment, based on developmental compartments, can help explain the dorsal abdomen of adult Drosophila. The anterior (A) compartment of each segment is subdivided into two domains of cells, each responding differently to Hedgehog. The anterior of these domains is non-neurogenic and clones lacking Notch develop normally; this domain can express stripe and form muscle attachments. The posterior domain is neurogenic and clones lacking Notch do not form cuticle; this domain is unable to express stripe or form muscle attachments. The posterior (P) compartment does not form muscle attachments. Our in vivo films indicate that early in the pupa the anterior domain of the A compartment expresses stripe in a narrowing zone that attracts the extending myotubes and resolves into the attachment sites for the dorsal abdominal muscles. We map the tendon cells precisely and show that all are confined to the anterior domain of A. It follows that the dorsal abdominal muscles are intersegmental, spanning from one anterior domain to the next. This view is tested and supported by clones that change cell identity or express stripe ectopically. It seems that growing myotubes originate in posterior A and extend forwards and backwards until they encounter and attach to anterior A cells. The dorsal adult muscles are polarised in the anteroposterior axis: we disprove the hypothesis that muscle orientation depends on genes that define planar cell polarity in the epidermis.

The paper presents possibilities of an economic evaluation of hard coal mines, using Cost Benefit Analysis (CBA). Suggested methodology for CBA applied to the economic evaluation of a mine allows to conduct a complex evaluation of mine’s functionality in connection to Polish conditions. Additionally to financial aspects, significant from the point of view of the mine’s owner, the paper includes social and environmental effects as a result of mining activities. Proposed methodology has undergone tests which used averaged data obtained from two selected hard coal mines located in the Upper Silesian Coal Basin. Presented results confirm the validity of social costs and benefits, and environmental losses resulting from mining operation, which were included in analysis comprehensively evaluating the efficiency of hard coal mines.