Co-option of epidermal cells enables touch sensing.

The epidermis is equipped with specialized mechanosensory organs that enable the detection of tactile stimuli. Here, by examining the differentiation of the tactile bristles, mechanosensory organs decorating the Drosophila adult epidermis, we show that neighbouring epidermal cells are essential for touch perception. Each mechanosensory bristle signals to the surrounding epidermis to co-opt a single epidermal cell, which we named the F-Cell.

Cortical Cyclin A controls spindle orientation during asymmetric cell divisions in Drosophila.

The coordination between cell proliferation and cell polarity is crucial to orient the asymmetric cell divisions to generate cell diversity in epithelia. In many instances, the Frizzled/Dishevelled planar cell polarity pathway is involved in mitotic spindle orientation, but how this is spatially and temporally coordinated with cell cycle progression has remained elusive. Using Drosophila sensory organ precursor cells as a model system, we show that Cyclin A, the main Cyclin driving the transition to M-phase of the cell cycle, is recruited to the apical-posterior cortex in prophase by the Frizzled/Dishevelled complex.

A neural progenitor mitotic wave is required for asynchronous axon outgrowth and morphology.

Spatiotemporal mechanisms generating neural diversity are fundamental for understanding neural processes. Here, we investigated how neural diversity arises from neurons coming from identical progenitors. In the dorsal thorax of , rows of mechanosensory organs originate from the division of sensory organ progenitor (SOPs).

Shaping of Neural Cell Lineages Through Coordination of Cell Proliferation and Cell Fate by the BTB-ZF Transcription Factor Tramtrack-69.

Cell diversity in multicellular organisms relies on coordination between cell proliferation and the acquisition of cell identity. The equilibrium between these two processes is essential to assure the correct number of determined cells at a given time at a given place. Using genetic approaches and correlative microscopy, we show that Tramtrack-69 (Ttk69, a Broad-complex, Tramtrack and Bric-à-brac - Zinc Finger (BTB-ZF) transcription factor ortholog of the human promyelocytic leukemia zinc finger factor) plays an essential role in controlling this balance.

Escargot and Scratch regulate neural commitment by antagonizing Notch activity in Drosophila sensory organs.

During Notch (N)-mediated binary cell fate decisions, cells adopt two different fates according to the levels of N pathway activation: an Noff-dependent or an Non-dependent fate. How cells maintain these N activity levels over time remains largely unknown. We address this question in the cell lineage that gives rise to the Drosophila mechanosensory organs.

G2 phase arrest prevents bristle progenitor self-renewal and synchronizes cell division with cell fate differentiation.

Developmentally regulated cell cycle arrest is a fundamental feature of neurogenesis, whose significance is poorly understood. During Drosophila sensory organ (SO) development, primary progenitor (pI) cells arrest in G2 phase for precisely defined periods. Upon re-entering the cell cycle in response to developmental signals, these G2-arrested precursor cells divide and generate specialized neuronal and non-neuronal cells.

CycA is involved in the control of endoreplication dynamics in the Drosophila bristle lineage.

Endocycles, which are characterised by repeated rounds of DNA replication without intervening mitosis, are involved in developmental processes associated with an increase in metabolic cell activity and are part of terminal differentiation. Endocycles are currently viewed as a restriction of the canonical cell cycle. As such, mitotic cyclins have been omitted from the endocycle mechanism and their role in this process has not been specifically analysed.

Laser microdissection of sensory organ precursor cells of Drosophila microchaetes.

Background: In Drosophila, each external sensory organ originates from the division of a unique precursor cell (the sensory organ precursor cell or SOP). Each SOP is specified from a cluster of equivalent cells, called a proneural cluster, all of them competent to become SOP. Although, it is well known how SOP cells are selected from proneural clusters, little is known about the downstream genes that are regulated during SOP fate specification.

Notch and Prospero repress proliferation following cyclin E overexpression in the Drosophila bristle lineage.

Understanding the mechanisms that coordinate cell proliferation, cell cycle arrest, and cell differentiation is essential to address the problem of how "normal" versus pathological developmental processes take place. In the bristle lineage of the adult fly, we have tested the capacity of post-mitotic cells to re-enter the cell cycle in response to the overexpression of cyclin E. We show that only terminal cells in which the identity is independent of Notch pathway undergo extra divisions after CycE overexpression.

S-phase favours notch cell responsiveness in the Drosophila bristle lineage.

We have studied cell sensitivity to Notch pathway signalling throughout the cell cycle. As model system, we used the Drosophila bristle lineage where at each division N plays a crucial role in fate determination. Using in vivo imaging, we followed this lineage and activated the N-pathway at different moments of the secondary precursor cell cycle.

The Ral/exocyst effector complex counters c-Jun N-terminal kinase-dependent apoptosis in Drosophila melanogaster.

Ral GTPase activity is a crucial cell-autonomous factor supporting tumor initiation and progression. To decipher pathways impacted by Ral, we have generated null and hypomorph alleles of the Drosophila melanogaster Ral gene. Ral null animals were not viable.

Cell cycle and cell-fate determination in Drosophila neural cell lineages.

"Normal" development requires a finely tuned equilibrium between cell differentiation and cell proliferation. Important issues in development include whether the cell cycle controls the cell-fate determination and whether cell identity in turn regulates cell-cycle progression. Although, these issues are of general biological relevance, stereotyped Drosophila neural lineages are particularly suited to address these questions and have provided insights into the links between cell-cycle progression and cell-fate specification.

Lethal giant larvae controls the localization of notch-signaling regulators numb, neuralized, and Sanpodo in Drosophila sensory-organ precursor cells.

Asymmetric distribution of fate determinants is a fundamental mechanism underlying the acquisition of distinct cell fates during asymmetric division. In Drosophila neuroblasts, the apical DmPar6/DaPKC complex inhibits Lethal giant larvae (Lgl) to promote the basal localization of fate determinants. In contrast, in the sensory precursor (pI) cells that divide asymmetrically with a planar polarity, Lgl inhibits Notch signaling in the anterior pI daughter cell, pIIb, by a yet-unknown mechanism.

Cell cycle diversity involves differential regulation of Cyclin E activity in the Drosophila bristle cell lineage.

In the Drosophila bristle lineage, five differentiated cells arise from a precursor cell after a rapid sequence of asymmetric cell divisions (one every 2 hours). We show that, in mitotic cells, this rapid cadence of cell divisions is associated with cell cycles essentially devoid of the G1-phase. This feature is due to the expression of Cyclin E that precedes each cell division, and the differential expression of the S-transition negative regulator, Dacapo.

Mother-daughter precursor cell fate transformation after Cdc2 down-regulation in the Drosophila bristle lineage.

The Drosophila bristle lineage is an excellent system in which to study how cell cycle and fate determination are synchronized in invariant cell lineages. In this model, five different cells arise from a single precursor cell, pI, after four asymmetric cell divisions. Cell diversity is achieved by the asymmetric segregation of cell determinants, such as Numb and Neuralized (Neur), resulting in differential activation of the Notch (N) pathway.

The glial cell undergoes apoptosis in the microchaete lineage of Drosophila.

Apoptosis plays a major role in vertebrate and invertebrate development. The adult Drosophila thoracic microchaete is a mechanosensory organ whose development has been extensively studied as a model of how cell division and cell determination intermingle. This sensory organ arises from a cell lineage that produces a glial cell and four other cells that form the organ.

Frizzled regulates localization of cell-fate determinants and mitotic spindle rotation during asymmetric cell division.

Cell-fate diversity is generated in part by the unequal segregation of cell-fate determinants during asymmetric cell divisions. In the Drosophila pupa, the pI sense organ precursor cell is polarized along the anterior-posterior axis of the fly and divides asymmetrically to generate a posterior pIIa cell and an anterior pIIb cell. The anterior pIIb cell specifically inherits the determinant Numb and the adaptor protein Partner of Numb (Pon).

Revisiting the Drosophila microchaete lineage: a novel intrinsically asymmetric cell division generates a glial cell.

The bristle mechanosensory organs of the adult fly are composed of four different cells that originate from a single precursor cell, pI, via two rounds of asymmetric cell division. Here, we have examined the pattern of cell divisions in this lineage by time-lapse confocal microscopy using GFP imaging and by immunostaining analysis. pI divided within the plane of the epithelium and along the anteroposterior axis to give rise to an anterior cell, pIIb, and a posterior cell, pIIa.

Frizzled signalling controls orientation of asymmetric sense organ precursor cell divisions in Drosophila.

During metazoan development, cell-fate diversity is brought about, in part, by asymmetric cell divisions. In Drosophila, bristle mechanosensory organs are composed of four different cells that originate from a single precursor cell, pI, after two rounds of asymmetric division. At each division, distinct fates are conferred on sister cells by the asymmetric segregation of Numb, a negative regulator of Notch signalling.

[Signalling by Notch family receptors].

From nematode to man, the transmembrane receptors of the Notch family act throughout embryonic and post-embryonic development to regulate the acquisition and/or maintenance of specific differentiative states. We will review here our current state of knowledge on Notch receptors structure and signalling activity.

Subcellular localization of Suppressor of Hairless in Drosophila sense organ cells during Notch signalling.

During imaginal development of Drosophila, Suppressor of Hairless [Su(H)], an evolutionarily conserved transcription factor that mediates intracellular signalling by the Notch (N) receptor, controls successive alternative cell fate decisions leading to the differentiation of multicellular sensory organs. We describe here the distribution of the Su(H) protein in the wing disc epithelium throughout development of adult sense organs. Su(H) was found to be evenly distributed in the nuclei of all imaginal disc cells during sensory organ precursor cells selection.

Control of cell fate choices by lateral signaling in the adult peripheral nervous system of Drosophila melanogaster.

The thoracic integument of the adult fruit fly is a relatively simple but highly patterned structure. It is composed of sensory organ cells distributed within a monolayer of epidermal cells. Both cell types are easily detected at the cuticular surface, as each external sense organ forms a sensory bristle and each epidermal cell secretes a small nonsensory hair.

Voltage-clamp analysis of gap junctions between embryonic muscles in Drosophila.

1. Intercellular communication between embryonic muscle fibres was examined in Drosophila melanogaster. 2.

The presynaptic cell determines the number of synapses in the Drosophila optic ganglia.

The role of the pre- and postsynaptic cells in determining the number of synapses has been investigated in retina mosaics of the gigas (gig) mutant of Drosophila. Mutant photoreceptors are two to three times larger than those of the wild type, while adjacent cells in the mosaic retina and the lamina are normal in size. Serial electron microscope reconstructions of mosaic lamina cartridges show that gig photoreceptors establish more synapses upon lamina neurons than the normal photoreceptors do.