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V Hartenstein

Publications and source records attributed to V Hartenstein.

At least 19 recordsLinked to original sources
PubMed2001

Embryonic development of the nervous system of the temnocephalid flatworm Craspedella pedum.

The nervous system of temnocephalid flatworms consists of the brain and three pairs of longitudinal connectives extending into the trunk and tail. The connectives are crosslinked by an invariant number of regularly spaced commissures. Branches of the connectives innervate the tentacles of the head and the sucker organ in the tail. A set of nerve rings encircling the pharynx and connected to the brain and connectives constitute the pharyngeal nervous system. The nervous system is formed during early embryogenesis when the embryo represents a multilayered mesenchymal mass of cells. Gastrulation and the formation of separate epithelial germ layers that characterize most other animal groups are absent. The brain arises as a bilaterally symmetric condensation of postmitotic cells in the deep layers of the anterior region of the embryonic mesenchyme. The pattern of axon outgrowth, visualized by labeling with anti-acetylated tubulin (acTub) antibody, shows marked differences from the pattern observed in other flatworm taxa in regard to the number of neurons that express the acTub epitope. Acetylated tubulin is only expressed in neurons that form long axon tracts. In other flatworm species, such as the typhloplanoid Mesostoma and the polyclad Imogine, which were investigated by us with the acTub antibody (Hartenstein and Ehlers [2000] Dev. Genes Evol. 210:399-415; Younossi-Hartenstein and Hartenstein [2000] Dev. Genes Evol. 210:383-398), only a small number of "pioneer neurons" become acTub positive during the embryonic period. By contrast, in temnocephalids, most, if not all, neurons express acTub and form long, large-diameter axons. Initially, the brain commissure, pharyngeal nerve ring, and the connectives are laid down. Commissural tracts and tentacle nerves branching off the connectives appear later. We speculate that the precocious differentiation of the nervous system may be related to the fact that temnocephalids move by muscle action, and possess a massive and complex muscular system when they hatch. In addition, they have muscular specializations such as the anterior tentacles and the posterior sucker that are used as soon as they hatch. By contrast, juveniles of Mesostoma and larvae of polyclads move predominantly by ciliary action that may not require a complex neural circuitry for coordination.

Animals↗
PubMed2001

The embryonic development of the temnocephalid flatworms Craspedella pedum and Diceratocephala boschmai.

We have analyzed the embryonic development of the temnocephalid flatworms Craspedella pedum and Diceratocephala boschmai, using a combination of fuchsin-labeled whole-mount preparation, histology, and transmission electron microscopy. Following the staging system recently introduced for another flatworm species (Mesostoma lingua), we can distinguish eight morphologically defined stages. Temnocephalids produce eggs of the neoophoran type in which a small oocyte is surrounded by a layer of yolk cells. Cleavage takes place in the center of the yolk mass (stages 1-2) and results in an irregular, multilayered disc of mesenchymal cells that moves to the future ventral egg pole (stage 3). Organ primordia, including those of the brain, pharynx, male genital apparatus, sucker, and epidermis "crystallize" within this disc without undergoing gastrulation movements (stage 4). An invagination of the epidermal primordium pushes the embryo back into the center of the yolk ("embryonic invagination"). As a result, organogenesis begins while the embryo is invaginated (stage 5). The brain differentiates into an outer cortex of cell bodies that surround a central neuropile. Precursor cells of the epidermis, pharynx, and protonephridia become organized into epithelia. During stage 6, the embryonic primordium everts back to the surface, where organogenesis and cell differentiation continues. Epidermal cells fuse into a syncytium that expands around the yolk. Myoblasts initially do not spread out in the way epidermal cells do; they remain concentrated in two narrow, longitudinal bands that extend along the sides of the embryo. Three pairs of axon tracts extending posteriorly from the brain follow the bands of myoblasts. Stages 7 and 8 are characterized by the appearance of eye pigmentation, brain condensation, and the formation of tentacles and a sucker that bud out from the epidermis of the anterior and posterior end, respectively. Comparison of morphogenesis in temnocephalids with observations in other flatworm taxa suggests a phylotypic stage for this phylum of invertebrates.

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PubMed2001

Dpp and Hh signaling in the Drosophila embryonic eye field.

We have analyzed the function of the Decapentaplegic (Dpp) and Hedgehog (Hh) signaling pathways in partitioning the dorsal head neurectoderm of the Drosophila embryo. This region, referred to as the anterior brain/eye anlage, gives rise to both the visual system and the protocerebrum. The anlage splits up into three main domains: the head midline ectoderm, protocerebral neurectoderm and visual primordium. Similar to their vertebrate counterparts, Hh and Dpp play an important role in the partitioning of the anterior brain/eye anlage. Dpp is secreted in the dorsal midline of the head. Lowering Dpp levels (in dpp heterozygotes or hypomorphic alleles) results in a 'cyclops' phenotype, where mid-dorsal head epidermis is transformed into dorsolateral structures, i.e. eye/optic lobe tissue, which causes a continuous visual primordium across the dorsal midline. Absence of Dpp results in the transformation of both dorsomedial and dorsolateral structures into brain neuroblasts. Regulatory genes that are required for eye/optic lobe fate, including sine oculis (so) and eyes absent (eya), are turned on in their respective domains by Dpp. The gene zerknuellt (zen), which is expressed in response to peak levels of Dpp in the dorsal midline, secondarily represses so and eya in the dorsomedial domain. Hh and its receptor/inhibitor, Patched (Ptc), are expressed in a transverse stripe along the posterior boundary of the eye field. As reported previously, Hh triggers the expression of determinants for larval eye (atonal) and adult eye (eyeless) in those cells of the eye field that are close to the Hh source. Eya and So, which are induced by Dpp, are epistatic to the Hh signal. Loss of Ptc, as well as overexpression of Hh, results in the ectopic induction of larval eye tissue in the dorsal midline (cyclopia). We discuss the similarities between vertebrate systems and Drosophila with regard to the fate map of the anterior brain/eye anlage, and its partitioning by Dpp and Hh signaling.

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PubMed2000

Specification of Drosophila hematopoietic lineage by conserved transcription factors.

Two major classes of cells observed within the Drosophila hematopoietic repertoire are plasmatocytes/macrophages and crystal cells. The transcription factor Lz (Lozenge), which resembles human AML1 (acute myeloid leukemia- 1) protein, is necessary for the development of crystal cells during embryonic and larval hematopoiesis. Another transcription factor, Gcm (glial cells missing), has previously been shown to be required for plasmatocyte development. Misexpression of Gcm causes crystal cells to be transformed into plasmatocytes. The Drosophila GATA protein Srp (Serpent) is required for both Lz and Gcm expression and is necessary for the development of both classes of hemocytes, whereas Lz and Gcm are required in a lineage-specific manner. Given the similarities of Srp and Lz to mammalian GATA and AML1 proteins, observations in Drosophila are likely to have broad implications for understanding mammalian hematopoiesis and leukemias.

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PubMed2000

Embryonic development of the nervous system of the rhabdocoel flatworm Mesostoma lingua (Abilgaard, 1789).

We have analyzed the embryonic development of the Mesostoma nervous system, using a combination of histology, transmission electron microscopy, and wholemount immunohistochemistry. Neural progenitors are formed at an early stage when the Mesostoma embryo constitutes a multilayered mesenchymal mass of cells. A neurectoderm as in vertebrates or arthropods is absent. Only after neurons in the deep layers of the embryo have started differentiating do superficial cells reorganize into an epithelium that will give rise to the epidermis. Neurons are clustered in two anterior, bilaterally symmetric brain hemispheres. An antibody against acetylated beta-tubulin (anti-acTub) that labels neurotubules reveals an invariant pattern of pioneer neurons in the brain of midstage embryos. Pioneer neurons are grouped in several small clusters at characteristic positions. They pioneer several commissural tracts of the brain and two pairs of ventral and dorsal connectives, respectively.

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PubMed2000

The embryonic development of the rhabdocoel flatworm Mesostoma lingua (Abildgaard, 1789).

The embryonic development of the flatworm Mesostoma lingua was studied using a combination of life observation and histological analysis of wholemount preparations and sections (viewed by both light and electron microscopy.) We introduce a series of stages defined by easily recognizable morphological criteria. These stages are also applicable to other platyhelminth taxa that are currently under investigation in our laboratory. During cleavage (stages 1 and 2), the embryo is located in the center of the egg, surrounded by a layer of yolk cells. After cleavage, the embryo forms a solid, disc-shaped cell cluster. During stage 3, the embryo migrates to the periphery of the egg and acquires bilateral symmetry. The side where it contacts the egg surface corresponds to the future ventral surface of the embryo. Stage 4 is the emergence of the first organ primordia, the brain and pharynx. Gastrulation, as usually defined by the appearance of germ layers, does not exist in Mesos-toma; instead, organ primordia emerge "in situ" from a mesenchymal mass of cells. Organogenesis takes place during stages 5 and 6. Cells at the ventral surface form the epidermal epithelium; inner cells differentiate into neurons, somatic and pharyngeal muscle cells, as well as the pharyngeal and protonephridial (excretory) epithelium. A junctional complex, consisting initially of small septate junctions, followed later by a more apically located zonula adherens, is formed in all epithelial tissues at stage 6. Beginning towards the end of stage 6 and continuing throughout stages 7 and 8, cytodifferentiation of the different organ systems takes place. Stage 7 is characterized by the appearance of eye pigmentation, brain condensation and spindle-shaped myocytes. Stage 8 describes the fully dorsally closed and differentiated embryo. Muscular contraction moves the body in the egg shell. We discuss Mesostoma embryogenesis in comparison to other animal phyla. Particular attention is given to the apparent absence of gastrulation and the formation of the epithelial junctional complex.

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PubMed2000

The embryonic development of the polyclad flatworm Imogine mcgrathi.

In this paper we describe the embryonic development of the polyclad flatworm Imogine mcgrathi. Imogine is an indirect developer that hatches as a planctonic Goette's larva after an embryonic period of approximately 7 days. Light and electron microscopic analyses of sections of staged embryos were combined with antibody stainings of wholemounted embryos to reconstruct the origin and movement of the primordia of the various organ systems, with particular emphasis on the nervous system. We introduce a system of morphologically defined stages aimed at facilitating future studies and cross-species comparisons among flatworm embryos. Imogine embryos undergo typical spiral cleavage. Micromere quartets 1-3 form an irregular double layer of mesenchymal cells that during gastrulation expands over micromere quartet 4. Micromere 4d divides into several large mesendodermal precursors whose position defines the ventral pole of the embryo. These cells, along with the animal micromeres that obtained a sub-surface position during cleavage, form a deep layer of cells that gives rise to all internal structures, including the nervous system, musculature, nephridia, and gut. Micromeres 4a-c are large yolky cells that are incorporated into the lumen of the gut, but do not themselves contribute to the gut epithelium. Shortly after gastrulation, cell differentiation sets in. Cells located at the surface adopt epithelial characteristics and form cilia that result in continuous movement of the post-gastrula stage embryo. Deep cells at the lateral margins of the embryo become organized into a protonephridial tube. A cluster of approximately 50 deep cells at the anterior pole forms the brain, in which we have identified sets of founder neurons of the brain commissure and the dorsal and ventral connectives. The early differentiating neurons, along with other cells forming stabilized microtubules (ciliated cells of the epidermis, gut and protonephridia; apical gland cells) could be analyzed in detail because of their labeling with an antibody against acetylated alpha-tubulin. Our findings indicate that, despite significant differences in the cleavage pattern and arrangement of blastomeres in the early embryo, morphogenesis and organ formation of a polyclad embryo follows a pattern that is very similar to the pattern observed by us and others in phylogenetically more evolved rhabdocoel flatworms.

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PubMed2000

Early development of the Drosophila mushroom body: the roles of eyeless and dachshund.

The mushroom body (MB) is a uniquely identifiable brain structure present in most arthropods. Functional studies have established its role in learning and memory. Here we describe the early embryonic origin of the four neuroblasts that give rise to the mushroom body and follow its morphogenesis through later embryonic stages. In the late embryo, axons of MB neurons lay down a characteristic pattern of pathways. eyeless (ey) and dachshund (dac) are expressed in the progenitor cells and neurons of the MB in the embryo and larva. In the larval brains of the hypomorphic ey(R) strain, we find that beside an overall reduction of MB neurons, one MB pathway, the medial lobe, is malformed or missing. Overexpression of eyeless in MBs under the control of an MB-specific promoter results in a converse type of axon pathway abnormality, i.e. malformation or loss of the dorsal lobe. In contrast, loss of dachshund results in deformation of the dorsal lobe, whereas no lobe abnormalities can be detected following dachshund overexpression. These results indicate that ey and dachshund may have a role in axon pathway selection during embryogenesis.

Animals↗
PubMed2000

Comparative approach to developmental analysis: the case of the dalyellid flatworm, Gieysztoria superba.

Dalyellida represents a taxon of small rhabdocoel flatworms that occur in freshwater habitats all over the world. Combining histology and electron microscopy we have analyzed the embryonic development of a new dalyellid species, Gieysztoria superba, in order to obtain more comparative data pertaining to morphogenesis and organogenesis in flatworms. We have used a morphological staging system that we recently introduced for another rhabdocoel, Mesostoma lingua (Younossi-Hartenstein et al., 2000). Our data show that in many fundamental respects, such as the irregular cleavage, mesenchymal embryonic primordium, and lack of gastrulation movements, Gieysztoria is highly similar to Mesostoma. During cleavage (stages 1 and 2) the embryo is located in the center of the egg where it is surrounded by a layer of yolk cells. Cleavage leads up to a solid, disc shaped cell cluster. During stage 3, the embryo migrates to the ventral side of the egg and acquires bilateral symmetry. Stages 4/5 sees the emergence of the first organ primordia, the brain, epidermis and pharynx. A peculiar invagination of the epidermal layer pushes the embryo back into the center of the yolk ("embryonic invagination"). Organogenesis takes place during stages 5 and 6 while the embryo is invaginated. A junctional complex, consisting initially of small septate junctions, followed later by a more apically located zonula adherens, is formed in all epithelial tissues, including epidermis, protonephridia, and pharynx. During late stages (6-8), Gieysztoria embryos evert back to the surface where the epidermal primordium expands and grows around the yolk to close dorsally. During this phase of development cytodifferentiation of the different organ systems takes place. Stage 7 is characterized by the appearance of eye pigmentation, brain condensation and spindle shaped myocytes. Stage 8 describes the fully dorsally closed and differentiated embryo. In comparison to other rhabdocoels, including Mesostoma, Gieysztoria exhibits a precocious differentiation of an intestinal epithelium and male genital apparatus. In Mesostoma, these structures are formed post hatching.

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PubMed1999

The role of cell adhesion molecules in Drosophila heart morphogenesis: faint sausage, shotgun/DE-cadherin, and laminin A are required for discrete stages in heart development.

Heart development in the Drosophila embryo starts with the specification of cardiac precursors from the dorsal edge of the mesoderm through signaling from the epidermis. Cardioblasts then become aligned in a single row of cells that migrate dorsally. After contacting their contralateral counterparts, cardioblasts undergo a cytoskeletal rearrangement and form a lumen. Its simple architecture and cellular composition makes the heart a good system to study mesodermal patterning, intergerm layer signaling, and the function of cell adhesion molecules (CAMs) during morphogenesis. In this paper we focus on three adhesion molecules, faint sausage (fas), shotgun/DE-cadherin (shg/DE-Cad), and laminin A (lam A), that are essential for heart development. fas encodes an Ig-like CAM and is required for the correct number of cardioblasts to become specified, as well as proper alignment of cardioblasts. shg/DE-Cad is expressed and required at a later stage than fas; in embryos lacking this gene, cardioblasts are specified normally and become aligned, but do not form a lumen. Additionally, cardioblasts of shg mutant embryos show a redistribution of phosphotyrosine as well as a loss of Armadillo from the membrane, indicating defects in cell polarity. The shg phenotype could be phenocopied by applying EGTA or cytochalasin D, supporting the view that Ca2+-dependent adhesion and the actin cytoskeleton are instrumental for heart lumen formation. As opposed to cell-cell adhesion, cell-substrate adhesion mechanisms are not required for heart morphogenesis, but only for maintenance of the differentiated heart. Embryos lacking the lam A gene initially developed a normal heart, but showed twists and breaks of cardioblasts at late embryonic stages. We discuss our findings in light of recent results that elucidate the function of different adhesion systems in vertebrate heart development.

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PubMed1999

The control of cell fate in the embryonic visual system by atonal, tailless and EGFR signaling.

We describe here the role of the transcription factors encoding genes tailless (tll), atonal (ato), sine oculis (so), eyeless (ey) and eyes absent (eya), and EGFR signaling in establishing the Drosophila embryonic visual system. The embryonic visual system consists of the optic lobe primordium, which, during later larval life, develops into the prominent optic lobe neuropiles, and the larval photoreceptor (Bolwig's organ). Both structures derive from a neurectodermal placode in the embryonic head. Expression of tll is normally confined to the optic lobe primordium, whereas ato appears in a subset of Bolwig's organ cells that we call Bolwig's organ founders. Phenotypic analysis, using specific markers for Bolwig's organ and the optic lobe, of tll loss- and gain-of-function mutant embryos reveals that tll functions to drive cells to optic lobe as opposed to Bolwig's organ fate. Similar experiments indicate that ato has the opposite effect, namely driving cells to a Bolwig's organ fate. Since we can show that tll and ato do not regulate each other, we propose a model wherein tll expression restricts the ability of cells to respond to signaling arising from ato-expressing Bolwig's organ pioneers. Our data further suggest that the Bolwig's organ founder cells produce Spitz (the Drosophila TGFalpha homolog) signal, which is passed to the neighboring secondary Bolwig's organ cells where it activates the EGFR signaling cascade and maintains the fate of these secondary cells. The regulators of tll expression in the embryonic visual system remain elusive, as we were unable to find evidence for regulation by the 'early eye genes' so, eya and ey, or by EGFR signaling.

Animals↗
PubMed1998

Embryonic development of the Drosophila brain. I. Pattern of pioneer tracts.

The neuropile of the late embryonic Drosophila brain can be subdivided into a vertical component (cervical connective), a transverse component (supraesophageal commissure), and a horizontal component for which we propose the term protocerebral connective. The core of each neuropile component is formed by numerous axon fascicles, the trajectory of which follows an invariant pattern. In the present study we have used an antibody against the adhesion molecule Fasciclin II (FasII) that is expressed in a large number of early differentiating neurons of the Drosophila embryo to follow the development of the axon tracts of the brain. The FasII antigen appears on the surface of clusters of neuronal somata prior to axon outgrowth. These clusters, for which we propose the term fibre tract founder clusters, are laid out in a linear pattern that forms an almost uninterrupted longitudinal track reaching from the ventral nerve cord to the "tip" of the brain. After expressing FasII on their soma, neurons of the fibre tract founder clusters extend axons that grow along the surface of the founder clusters and form a simple system of pioneer tracts for each of the components of the brain neuropile. We have reconstructed the FasII-positive fibre tract founder clusters and their axons from optical sections and generated digital 3-D models that illustrate the spatial relationships of the pioneer tracts. Three fibre tract founder clusters, D/T, P1, and P3m, pioneer the cervical connective. P21 and P2m form a transverse track that pioneers the supraesophageal commissure. P4m and P41/P51/VP5m form two tracts that pioneer a medial and a lateral component of the protocerebral connective, respectively. Because FasII expression continues uninterruptedly into the larval period when the "rudiments" of many parts of the adult neuropile are readily identifiable, it was possible to assign several of the embryonic pioneer tracts to definitive neuropile components, including the median bundle, antennocerebral tract, mushroom body, and posterior optic tract.

Age Factors↗
PubMed1998

Embryonic development of the Drosophila brain. II. Pattern of glial cells.

Glial cells in Drosophila and other insects are organized in an outer layer that envelops the surface of the central and peripheral nervous system (subperineurial glia, peripheral glia), a middle layer associated with neuronal somata in the cortex (cell body glia), and an inner layer surrounding the neuropile (longitudinal glia, midline glia, nerve root glia). In the ventral nerve cord, most glial cells are formed by a relatively small number of neuro-glioblasts; subsequently, glial cell precursors migrate and spread out widely to reach their final destination. By using a glia-specific marker (antibody against the Repo protein) we have reconstructed the pattern of glial cell precursors at successive developmental stages, focusing on the glia of the supraesophageal ganglion and subesophageal ganglion which are not described in previous studies. Digitized images of consecutive optical sections were used to generate 3-D models that show the spatial pattern of glial cell precursors in relationship to the neuropile, brain surface, and peripheral nerves. Similar to their spatial organization in the ventral nerve cord, glial cells of the brain populate the brain nerves and outer surface, cortical cell body layer, and cortex-neuropile interface. Neuropile-associated glial cells arise from a cluster located at the base of the supraesophageal ganglion; from this position, they migrate dorsally along the developing axon tracts and by late embryonic stages form a sheath around all neuropile compartments, including the supraesophageal commissure. Surface and cell body glial cells derive from several discrete foci, notably two large clusters at the deuterocerebrum/protocerebrum boundary and the posterior protocerebrum. From these foci, glial cells then fan out to envelop the surface of the supraesophageal ganglion.

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PubMed1998

The role of morphogenetic cell death during Drosophila embryonic head development.

This article addresses the role of programmed cell death (apoptosis) during embryonic head development of Drosophila. Previous studies showed that reaper (rpr) is expressed in and required by cells undergoing apoptosis. We have analyzed the correlation between the pattern of expression of rpr and morphogenetic movements affecting head development. Furthermore, we have investigated the defects in head development resulting from the absence of apoptosis in embryos deficient for rpr. Our results show that, in the head, domains of high incidence of cell death as marked by expression of rpr correlate with regions where most morphogenetic movements occur; these regions are involved in formation of mouth structures, the internalization of neural progenitors, and head involution. Cellular events driving these movements are delamination, invagination, and intercalation as well as disruption and reformation of contacts among epithelial cells. The analysis of rpr-deficient embryos demonstrates that, despite of the widespread occurrence of apoptosis during normal head morphogenesis, many aspects of this process proceed in an apparently unperturbed manner even when cell death is blocked. In particular, movements that happen early during embryonic development and that are evolutionarily more ancient (e.g., formation of the dorsal ridge and the pharynx) take place almost normally in rpr-deficient embryos. Later events which are mostly associated with head involution (e.g., retraction of the clypeolabrum, formation of the dorsal pouch, fusion of lateral gnathal lobes) are evolutionarily more recent and fail to occur normally in rpr-deficient embryos.

Animals↗
PubMed1998

faint sausage encodes a novel extracellular protein of the immunoglobulin superfamily required for cell migration and the establishment of normal axonal pathways in the Drosophila nervous system.

We examined the structure of the nervous system in Drosophila embryos homozygous for a null mutation in the faint sausage (fas) gene. In the peripheral nervous system (PNS) of fas mutants, neurons fail to delaminate from the ectodermal epithelium; in the central nervous system (CNS), the positions of neuronal cell bodies and glial cells are abnormal and normal axonal pathways do not form. Sequence analysis of fas cDNAs revealed that the fas protein product has characteristics of an extracellular protein and that it is a novel member of the immunoglobulin (Ig) superfamily. In situ hybridization demonstrated that fas transcripts are expressed throughout the embryo but they are in relatively high concentrations in the lateral ectoderm, from which the peripheral nervous system delaminates and in the CNS. Antiserum directed against Fas protein was found to stain neurons but not glia in the CNS. We conclude that fas encodes a protein that, in the developing nervous system, is present on the surface of neurons and is essential for nerve cell migration and the establishment of axonal pathways.

Amino Acid Sequence↗
PubMed1998

EGFR signaling is required for the differentiation and maintenance of neural progenitors along the dorsal midline of the Drosophila embryonic head.

EGFR signaling has been shown in recent years to be involved in the determination, differentiation and maintenance of neural and epidermal cells of the ventral midline (mesectoderm and ventromedial ectoderm). Localized activation of the TGFalpha homolog Spitz (Spi) in the mesectoderm is achieved by the products of the genes rhomboid and Star. Spi binds to its receptor, the Drosophila epidermal growth factor receptor homolog (Egfr), and triggers the Ras pathway which is needed for the survival and differentiation of ventral midline cells. The results reported here indicate that EGFR signaling is also required in a narrow medial domain of the head ectoderm (called 'head midline' in the following) that includes the anlagen of the medial brain, the visual system (optic lobe, larval eye) and the stomatogastric nervous system (SNS). We document that genes involved in EGFR signaling are expressed in the head midline. Loss of EGFR signaling results in an almost total absence of optic lobe and larval eye, as well as severe reduction of SNS and medial brain. The cellular mechanism by which this phenotype arises is a failure of neurectodermal cells to differentiate combined with apoptotic cell death. Overactivity of EGFR signaling, as achieved by heat-shock-driven activation of a wild-type rhomboid (rho) construct, or by loss of function of argos (aos) or yan, results in an hyperplasia and deformity of the head midline structures. We show that, beside their requirement for EGFR signaling, head and ventral midline structures share several morphogenetic and molecular properties.

Animals↗
PubMed1997

Structure and spatial pattern of the sensilla of the body segments of insect larvae.

We describe the types and patterns of sensilla present on the thorax and abdomen of newly hatched larvae of representative species of several insect orders, among them Saltatoria, Mantodea, Blattaria, Heteroptera, Lepidoptera, and Diptera. Sensilla of non-Dipteran species almost exclusively comprise mechanoreceptive hairs or bristles (trichoid sensilla) of various sizes and numbers. In higher Dipterans, peg sensilla (sensilla basiconica, sensilla coeloconica) and so-called papilla sensilla predominate. The pattern of early larval sensilla falls into three main classes, which can be described as 1) fixed pattern, 2) variable pattern, and 3) variable pattern with fixed elements. In larvae exhibiting a fixed sensillum pattern (found in all Dipteran species investigated), sensilla are invariant in number; they are precisely placed in relationship to each other and typically form a single row behind the middle of each segment. A variable pattern (common in most insect groups) typically consists of several rows of relatively evenly spaced sensilla encircling the middle of each segment. In animals with a variable pattern including fixed elements, some sensilla, recognizable by their size or shape, are precisely placed, whereas other sensilla surrounding them are variable.

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