Takashi Adachi-Yamada

E-cadherin prolongs the moment for interaction between intestinal stem cell and its progenitor cell to ensure Notch signaling in adult Drosophila midgut

Intestinal stem cells (ISCs) are required for maintenance of the proper cell composition in the adult intestine. To ensure permanent recruitment of newly differentiated cells, the ISC undergoes asymmetric cell division that generates an ISC itself and a progenitor cell. In the Drosophila midgut, cell fate for the absorptive cell is determined by Notch (N) signal in the progenitor cells that receive a ligand Delta (Dl) produced by the ISCs. Although most of the ISCs and progenitor cells are distantly located, they should retain their attachment when N is activated because the Dl–N interaction requires cell adhesion. Furthermore, N cannot be activated before completion of cell division. Thus, the moment after cell division and before cell separation should be prolonged for certain N activation, although the mechanism for this remains unclear. Here, we demonstrate that E‐cadherin (E‐cad) is required for stable attachment between the two cells. When E‐cad does not function, N is not activated and cell differentiation is attenuated. We also show that the ISC tumor by N inactivation is assisted by a defect in E‐cad down‐regulation. These findings reveal one of the normal N functions used to inhibit tumorigenesis through lowering of E‐cad for proper midgut cell turnover.

Wing-to-Leg Homeosis by Spineless Causes Apoptosis Regulated by Fish-lips, a Novel Leucine-Rich Repeat Transmembrane Protein

ABSTRACT Growth, patterning, and apoptosis are mutually interactive during development. For example, cells that select an abnormal fate in a developing field are frequently removed by apoptosis. An important issue in this process that needs to be resolved is the mechanism used by cells to discern their correct fate from an abnormal fate. In order to examine this issue, we developed an animal model that expresses the dioxin receptor homolog Spineless (Ss) ectopically in the Drosophila wing. The presence of mosaic clones ectopically expressing ss results in a local transformation of organ identity, homeosis, from wing into a leg or antenna. The cells with misspecified fates subsequently activate c-Jun N-terminal kinase to undergo apoptosis in an autonomous or nonautonomous manner depending on their position within the wing, suggesting that a cell-cell interaction is, at least in some cases, involved in the detection of misspecified cells. Similar position dependence is commonly observed when various homeotic genes controlling the body segments are ectopically expressed. The autonomous and nonautonomous apoptosis caused by ss is regulated by a novel leucine-rich repeat family transmembrane protein, Fish-lips (Fili) that interacts with surrounding normal cells. These data support a mechanism in which the lack of some membrane proteins helps to recognize the presence of different cell types and direct these cells to an apoptotic fate in order to exclude them from the normal developing field.

The Homeodomain Protein Defective Proventriculus Is Essential for Male Accessory Gland Development to Enhance Fecundity in Drosophila

The Drosophila male accessory gland has functions similar to those of the mammalian prostate gland and the seminal vesicle, and secretes accessory gland proteins into the seminal fluid. Each of the two lobes of the accessory gland is composed of two types of binucleate cell: about 1,000 main cells and 40 secondary cells. A well-known accessory gland protein, sex peptide, is secreted from the main cells and induces female postmating response to increase progeny production, whereas little is known about physiological significance of the secondary cells. The homeodomain transcriptional repressor Defective proventriculus (Dve) is strongly expressed in adult secondary cells, and its mutation resulted in loss of secondary cells, mononucleation of main cells, and reduced size of the accessory gland. dve mutant males had low fecundity despite the presence of sex peptide, and failed to induce the female postmating responses of increased egg laying and reduced sexual receptivity. RNAi-mediated dve knockdown males also had low fecundity with normally binucleate main cells. We provide the first evidence that secondary cells are crucial for male fecundity, and also that Dve activity is required for survival of the secondary cells. These findings provide new insights into a mechanism of fertility/fecundity.

RNAi-Mediated Knockdown Showing Impaired Cell Survival in Drosophila Wing Imaginal Disc

The genetically amenable organism Drosophila melanogaster has been estimated to have 14,076 protein coding genes in the genome, according to the flybase release note R5.13 (http://flybase.bio.indiana.edu/static_pages/docs/release_notes.html). Recent application of RNA interference (RNAi) to the study of developmental biology in Drosophila has enabled us to carry out a systematic investigation of genes affecting various specific phenotypes. In order to search for genes supporting cell survival, we conducted an immunohistochemical examination in which the RNAi of 2,497 genes was independently induced within the dorsal compartment of the wing imaginal disc. Under these conditions, the activities of a stress-activated protein kinase JNK (c-Jun N-terminal kinase) and apoptosis-executing factor Caspase-3 were monitored. Approximately half of the genes displayed a strong JNK or Caspase-3 activation when their RNAi was induced. Most of the JNK activation accompanied Caspase-3 activation, while the opposite did not hold true. Interestingly, the area activating Caspase-3 was more broadly seen than that activating JNK, suggesting that JNK is crucial for induction of non-autonomous apoptosis in many cases. Furthermore, the RNAi of essential factors commonly regulating transcription and translation showed a severe and cell-autonomous apoptosis but also elicited another apoptosis at an adjacent area in a non-autonomous way. We also found that the frequency of apoptosis varies depending on the tissues.

Cell death and selective adhesion reorganize the dorsoventral boundary for zigzag patterning of Drosophila wing margin hairs

Animal tissues and organs are comprised of several types of cells, which are often arranged in a well-ordered pattern. The posterior part of the Drosophila wing margin is covered with a double row of long hairs, which are equally and alternately derived from the dorsal and ventral sides of the wing, exhibiting a zigzag pattern in the lateral view. How this geometrically regular pattern is formed has not been fully understood. In this study, we show that this zigzag pattern is created by rearrangement of wing margin cells along the dorsoventral boundary flanked by the double row of hair cells during metamorphosis. This cell rearrangement is induced by selective apoptosis of wing margin cells that are spatially separated from hair cells. As a result of apoptosis, the remaining wing margin cells are rearranged in a well-ordered manner, which shapes corrugated lateral sides of both dorsal and ventral edges to interlock them for zigzag patterning. We further show that the corrugated topology of the wing edges is achieved by cell-type specific expression and localization of four kinds of NEPH1/nephrin family proteins through heterophilic adhesion between wing margin cells and hair cells. Homophilic E-cadherin adhesion is also required for attachment of the corrugated dorsoventral edges. Taken together, our results demonstrate that sequential coordination of apoptosis and epithelial architecture with selective adhesion creates the zigzag hair alignment. This may be a common mechanism for geometrically ordered repetitive packing of several types of cells in similarly patterned developmental fields such as the mammalian organ of Corti.

Isoform-specific functions of Mud/NuMA mediate binucleation of Drosophila male accessory gland cells

BackgroundIn standard cell division, the cells undergo karyokinesis and then cytokinesis. Some cells, however, such as cardiomyocytes and hepatocytes, can produce binucleate cells by going through mitosis without cytokinesis. This cytokinesis skipping is thought to be due to the inhibition of cytokinesis machinery such as the central spindle or the contractile ring, but the mechanisms regulating it are unclear. We investigated them by characterizing the binucleation event during development of the Drosophila male accessory gland, in which all cells are binucleate.ResultsThe accessory gland cells arrested the cell cycle at 50xa0hours after puparium formation (APF) and in the middle of the pupal stage stopped proliferating for 5xa0hours. They then restarted the cell cycle and at 55xa0hours APF entered the M-phase synchronously. At this stage, accessory gland cells binucleated by mitosis without cytokinesis. Binucleating cells displayed the standard karyokinesis progression but also showed unusual features such as a non-round shape, spindle orientation along the apico-basal axis, and poor assembly of the central spindle. Mud, a Drosophila homolog of NuMA, regulated the processes responsible for these three features, the classical isoform MudPBD and the two newly characterized isoforms MudL and MudS regulated them differently: MudL repressed cell rounding, MudPBD and MudS oriented the spindle along the apico-basal axis, and MudS and MudL repressed central spindle assembly. Importantly, overexpression of MudS induced binucleation even in standard proliferating cells such as those in imaginal discs.ConclusionsWe characterized the binucleation in the Drosophila male accessory gland and examined mechanisms that regulated unusual morphologies of binucleating cells. We demonstrated that Mud, a microtubule binding protein regulating spindle orientation, was involved in this binucleation. We suggest that atypical functions exerted by three structurally different isoforms of Mud regulate cell rounding, spindle orientation and central spindle assembly in binucleation. We also propose that MudS is a key regulator triggering cytokinesis skipping in binucleation processes.

Mathematical modelling and experiments for the proliferation and differentiation of Drosophila intestinal stem cells II

We study the proliferation and differentiation of stem cells in the Drosophila posterior midgut epithelium, which mainly consists of intestinal stem cells (ISCs); semi-differentiated cells, i.e. enteroblasts (EBs); and two types of fully differentiated cells, i.e. enteroendocrine cells (EEs) and enterocytes (ECs). The cellular system of ISCs is controlled by Wnt and Notch signalling pathways. In this article, we experimentally show that EBs are not capable of efficiently differentiating into ECs in the absence of Wnt signalling. On the basis of the experimental results and known facts, we propose a scheme and a simple ordinary differential equation (ODE) model for the proliferation and differentiation of ISCs. This is a first step towards understanding the universal mechanism for the maintenance of the cellular system of tissue stem cells controlled by signalling pathways.

Repair responses to abnormalities in morphogen activity gradient

Establishing and maintaining a morphogen gradient are important in the growth and patterning of developing organs. When a discontinuity in a morphogen signal gradient is created by somatic mutant clones with aberrant intensities of morphogen signals within the Drosophila wing disc, the clones can be removed by apoptosis to restore the morphogen signal gradient. This apoptosis is termed “morphogenetic apoptosis” and has been observed to occur in a cell autonomous or non‐cell autonomous manner. This review discusses possible molecular mechanisms of both autonomous and non‐cell autonomous apoptosis in addition to similar cellular events in reference to recent findings.

Apoptosis During Cellular Pattern Formation

We can all see a variety of ordered cellular patterns consisting of various cell types, throughout nature. It is surprising that these ordered cellular patterns are created reproducibly during development in all individuals. Elucidating their underlying molecular mechanisms has been an interesting research subject for developmental biologists. The essential building blocks in these processes are cell proliferation, cell shape change, cell movement, and apoptosis. These cellular behaviors must be coordinated through cell-cell communication.