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M Bate

Publications and source records attributed to M Bate.

At least 55 records · Page 3Linked to original sources
PubMed1993

A dual requirement for neurogenic genes in Drosophila myogenesis.

In wild-type embryos of Drosophila melanogaster, the formation of differentiated larval muscles is preceded by the segregation of small numbers of progenitor or founder cells in the embryonic mesoderm. The founder cells, characterised by the expression of genes encoding putative transcription factors such as S59 or vestigial, fuse with neighbouring myoblasts to form syncytial precursors of individual muscles. Founder cell segregation is deranged in embryos mutant for any of the neurogenic genes: enlarged clusters of cells expressing S59 or vestigial are detected at the sites where small numbers of founder cells segregate in the wild type. In addition, muscle differentiation is deranged in such embryos in a way that appears to be closely linked to the extent of epidermal disruption caused by the neurogenic phenotype: myoblast fusion is limited to regions of the mesoderm beneath the residual epidermis left by the hyperplasia of the nervous system, and late expression of S59 and vestigial is lost from mesoderm not lying within the margins of the residual epidermis. Thus neurogenic gene functions appear to be required both for the normal segregation of founder cells and for muscle differentiation. It is not clear whether either of these requirements reflects an essential function for any or all of the neurogenic genes within the mesoderm itself.

Animals↗
PubMed1993

From growth cone to synapse: the life history of the RP3 motor neuron.

In Drosophila, the ability to analyze the development of individually identified neurons with a variety of imaging and biophysical techniques can be complemented by sophisticated genetics and molecular biology. This powerful combination is allowing the development and function of single neurons and their synaptic connections to be unraveled at an unparalleled level of resolution. In this article, we focus on a single, identified motoneuron--RP3--arguably the best understood neuron in the fruitfly. Many events in the life history of RP3 are well characterized, including cell migration, axon outgrowth and pathfinding within the central nervous system, pathfinding in the periphery to its appropriate muscle target domain, the specific recognition of its muscle targets, the events of synapse formation and maturation, and its mature function in the locomotion of the fly larva. Genetic analysis has revealed mutations in a number of different genes which affect specific aspects of RP3 development from axon outgrowth to synapse formation.

Animals↗
PubMed1993

Myogenesis and muscle patterning in Drosophila.

Subsets of differentiating muscles in the Drosophila embryo express putative transcription factors, such as S59 and vestigial. These genes may control the development of specific muscle properties. Myogenesis in embryos mutant for wingless is grossly deranged. Mesodermal expression of S59 is lost, whereas some vestigial-expressing muscles develop. wingless dependence and independence of specific muscle subsets correlates with an early derangement of twist expression in wingless mutants. The possible role of the ectoderm in patterning Drosophila mesoderm is discussed.

Animals↗
PubMed1993

Development of the embryonic neuromuscular synapse of Drosophila melanogaster.

We have examined the embryonic development of an identified neuromuscular junction (NMJ) of Drosophila melanogaster using whole-cell patch-clamp and a variety of physiological and morphological techniques. Synaptic current at the embryonic NMJ is carried through a large-conductance (200 pS) L-glutamate receptor. Early synaptic communication is characterized by frequent, brief (< 10 msec) currents carried through few (1-10) receptors and relatively rare, prolonged currents (up to seconds) of similar amplitude. The brief currents have a time course similar to the mature larval excitatory junction currents (EJCs), but the prolonged currents are restricted to early stages of synaptogenesis. The amplitude of EJCs rapidly increases, and the frequency of the prolonged currents decreases, after the initial stages of synaptogenesis. Early prolonged (seconds), nonspiking synaptic potentials are replaced with rapid (< 0.10 sec), spiking synaptic potentials later in development. The early synapse appears tenuous, easily fatiguable, and with inconsistent communication properties. Synaptogenesis can be divided into a sequence of progressive stages. (1) Motor axon filopodia begin neurotransmitter expression and concurrent exploration of the myotube surface. (2) Myotubes uncouple to form single-cell units soon after motor axon contact. (3) A small number of transmitter receptors are homogeneously displayed on the myotube surface immediately following myotube uncoupling. (4) Endogenous transmitter release from pioneering growth cones is detected; nerve stimulation elicits postsynaptic EJC response. (5) Motor axon filopodia and transmitter receptors are localized to the mature synaptic zone; filopodial localization is complete in advance of receptor localization. (6) A functional neuromuscular synapse is formed; endogenous muscular activity begins; nerve stimulation leads to muscle contraction. (7) Morphological presynaptic specializations develop; synapse develops mature morphology. (8) A second motor axon synapses on the myotube at the pre-established synaptic zone. (9) Vigorous neuromuscular activity, characteristic of larval locomotory movements, begins. (10) A second stage of receptor expression begins and continues through the end of embryogenesis. In general, Drosophila neuromuscular synaptogenesis appears similar to neuromuscular synaptogenesis in known vertebrate preparations. We suggest that this system provides a model for synaptogenesis in which investigation can be readily extended to a genetic and molecular level.

Animals↗
PubMed1993

Development of larval muscle properties in the embryonic myotubes of Drosophila melanogaster.

The entire developmental history of muscle membrane electrogenesis can be observed in the embryonic myotubes of Drosophila. We have examined the development of ionic currents and muscle properties using whole-cell patch-clamp techniques throughout embryonic myogenesis. In the early stages of myogenesis, from myoblast fusion through to establishing epidermal insertions, the myotubes are electrically inert and are electrically and dye coupled to adjacent myotubes. Membrane electrogenesis begins in the mid-embryonic stages (early stage 16), when the myotubes abruptly uncouple, revealing the first of five prominent extrajunctional currents: a small, inward, voltage-gated calcium current (ICa). The uncoupling of the embryonic myotubes heralds the onset of extremely rapid electrogenesis; within several minutes both the fast, inactivating (IA; Shaker) and delayed, noninactivating (IK) outward potassium currents, the stretch-activated outward potassium current, and the junctional glutamate-gated inward current all appear and begin to develop in a current-specific manner. Very late in embryogenesis (late stage 17), the calcium-dependent, outward potassium currents [rapid, inactivating (ICF; slowpoke) then delayed, noninactivating (ICS)] develop, completing the complement of macroscopic currents in the mature larval muscle. Hence, the voltage-gated currents (ICa, IA, and IK, respectively) appear relatively early, and the calcium-dependent currents (ICF, ICS) appear only very late during myogenesis. This developmental progression of current maturation is reflected in dynamic changes in the voltage responses of the embryonic membrane, from wholly passive response to current injection in the early, coupled myotubes to regenerating, overshooting action potentials in the mature embryonic muscle. The earliest embryonic IA current has a midpoint of inactivation 40 mV more negative than the IA current in the mature embryo. As myogenesis proceeds, the inactivation curve develops a biphasic character, suggesting that a low-inactivation IA channel is present in early development and progressively replaced by the mature form as development proceeds. The current at all stages can be completely eliminated in Shaker mutants (ShKS133). These findings suggest that an embryonic form of the Shaker IA channel is present during early myogenesis. The prominent IA current present in early development is almost entirely inactivated at the physiological resting potential; the significance and mechanism of this developmental shift are unclear.

Animals↗
PubMed1991

The embryonic origin of imaginal discs in Drosophila.

The thoracic imaginal discs of Drosophila melanogaster can be observed during embryogenesis as clusters of cells with particular shapes, sizes and behaviours. These structures can be detected soon after germ band shortening and their development appears to be tightly linked to that of the larval epidermis.

Animals↗
PubMed1991

The development of adult muscles in Drosophila: ablation of identified muscle precursor cells.

A small subset of mesodermal cells continues to express twist in the late embryo of Drosophila. These cells are the precursors of adult muscles. Each late twist-expressing cell begins to divide early in the second larval instar and division continues throughout the second and third instars, resulting in a small clone of twist-expressing cells at puparium formation. Treatment with a DNA-synthesis inhibitor, hydroxyurea (HU), ablates these cells if applied during S-phase of their replication cycle. We ablated twist-expressing lineages in the larva and demonstrated that this results in the absence of subsets of muscles in the adult abdomen and leg. HU treatment during this larval period has no discernible effect on the adult epidermis or innervation. We conclude that the twist-expressing cells identified in the late embryo are the unique primordia of adult muscles. Each primordium is fated to establish 6-10 adult muscle fibres, defined here as a 'muscle fibre group'. Each primordium has a unique fate and, after ablation, is not replaced by neighbouring cells. This unique fate does not rest with a particular founder cell within the primordium but is specified at the primordium level: ablation of a subset of cells within a muscle primordium does not result in an ablation of the resulting muscle group or in a decrease in the number of fibres within that muscle group, but rather results in a uniform decrease in the number of nuclei/fibres throughout the entire muscle. Thus, the twist-expressing primordia in the abdomen appear to be fated to give rise to a particular muscle group but act as an equivalent precursor pool in the formation of that muscle group. Our results permit the conclusion that specific muscle groups in the adult leg arise from restricted pools of twist-expressing adepithelial cells in the larval imaginal disc in a similar fashion. We conclude that the fate restriction of myoblast pools in early development defines elements of the final adult muscle pattern. The fate restriction of myoblast cells may be a result of genetic determination to form a specified muscle group or, alternatively, reflect the spatial isolation of otherwise equivalent cells to form muscle-specific precursor pools.

Abdomen↗
PubMed1991

Development of the indirect flight muscles of Drosophila.

We have followed the pupal development of the indirect flight muscles (IFMs) of Drosophila melanogaster. At the onset of metamorphosis larval muscles start to histolyze, with the exception of a specific set of thoracic muscles. Myoblasts surround these persisting larval muscles and begin the formation of one group of adult indirect flight muscles, the dorsal longitudinal muscles. We show that the other group of indirect flight muscles, the dorsoventral muscles, develops simultaneously but without the use of larval templates. By morphological criteria and by patterns of specific gene expression, our experiments define events in IFM development.

Animals↗
PubMed1991

Cells with persistent twist expression are the embryonic precursors of adult muscles in Drosophila.

twist expression in the embryonic mesoderm of Drosophila declines during germ band retraction to leave a residual population of twist-expressing cells in the late embryo. In the abdomen, the pattern of twist expression is a simple one: a single cell ventrally, pairs of cells laterally and three cells dorsally in each hemisegment. In the thorax, there are patches of cells associated with the imaginal discs and there are additional clusters in A8 and A9. During larval life, the twist-expressing cells proliferate and, in the abdomen, they form ventral, lateral and dorsal clusters, which are the precursors of the adult abdominal muscles, while in the thorax, they form populations of cells in the imaginal discs that correspond to the adepithelial cells described by previous authors. While most thoracic twist-expressing cells are associated with the discs, the abdominal cells are separate from the precursors of the adult abdominal epidermis, the abdominal histoblasts, and lie on branches of peripheral nerves. The distribution of these cells is tightly linked to the pattern of peripheral nerves, but they segregate normally in da/da embryos despite the absence of the peripheral nervous system.

Animals↗
PubMed1991

The development of adult abdominal muscles in Drosophila: myoblasts express twist and are associated with nerves.

During metamorphosis, the adult muscles of the Drosophila abdomen develop from pools of myoblasts that are present in the larva. The adult myoblasts express twist in the third larval instar and the early pupa and are closely associated with nerves. Growing adult nerves and the twist-expressing cells migrate out across the developing abdominal epidermis, and as twist expression declines, the myoblasts begin to synthesize beta 3 tubulin. There follows a process involving cell fusion and segregation into cell groups to form multinucleate muscle precursors. These bipolar precursors migrate at both ends to find their correct attachment points. beta 3 tubulin expression continues at least until 51 h APF by which time the adult muscle pattern has been established.

Abdomen↗
PubMed1990

Expression of a MyoD family member prefigures muscle pattern in Drosophila embryos.

We have isolated a Drosophila gene that is expressed in a temporal and spatial pattern during embryogenesis, strongly suggesting an important role for this gene in the early development of muscle. This gene, which we have named nautilus (nau), encodes basic and helix-loop-helix domains that display striking sequence similarity to those of the vertebrate myogenic regulatory gene family. nau transcripts are initially localized to segmentally repeated clusters of mesodermal cells, a pattern that is reminiscent of the expression of the achaete-scute genes in the Drosophila peripheral nervous system. These early nau-positive cells are detected just prior to the first morphological evidence of muscle cell fusion and occupy similar positions as the later-appearing muscle precursors. Subsequently, nau transcripts are present in at least a subset of growing muscle precursors and mature muscle fibers that exhibit distinct segmental differences. These observations establish nau as the earliest known marker of myogenesis in Drosophila and indicate that this gene may be a key determinant of pattern formation in the embryonic mesoderm.

Amino Acid Sequence↗
PubMed1990

Immunological, biochemical and physiological analyses of cardioacceleratory peptide 2 (CAP2) activity in the embryo of the tobacco hawkmoth Manduca sexta.

The cells in the embryonic CNS of the tobacco hawkmoth, Manduca sexta, that synthesize a cardioacceleratory peptide 2 (CAP2)-like antigen were identified using immunohistochemical techniques. Two distinct neurosecretory cell types were present in the abdominal ventral nerve cord (VNC) that contain CAP2-like immunoreactivity during late embryogenesis: a pair of large (diameter range 15-20 microns) cells lying along the posterior, dorsal midline of abdominal ganglia A4-A8, and a bilateral set of four smaller (diameter range 6-11 microns) neurons which lie at the base of each ventral root in abdominal ganglia A2-A8. CAP2-like accumulation appeared to follow independent patterns in the two cell types. CAP2-like immunoreactivity began at 60% of embryo development (DT) in the medial cells, accumulated steadily throughout embryogenesis, and dropped markedly during hatching. Lateral cells synthesized the CAP2-like antigen later in development (70% DT) and showed a sharp drop in antigen levels between 75% and 80% of embryonic development. Extracts from developing M. sexta embryos were found to contain a cardioactive factor capable of accelerating the contraction frequency of the pharate adult moth heart in a fashion similar to CAP2. Immunoprecipitation with a monoclonal antibody that specifically recognizes the two endogenous Manduca cardioacceleratory peptides and purification using high pressure liquid chromatography identified this factor as cardioacceleratory peptide 2 (CAP2). Using an in vitro heart bioassay, the levels of this cardioactive neuropeptide were traced during the development of the M. sexta embryo. As with the immunohistochemical results, two periods during embryogenesis were identified in which the level of CAP2 dropped markedly: between 75% and 80% development, and at hatching. Embryo bioassays of CAP2 activity were used to identify possible target tissues for physiological activity during these two putative release times. CAP2 was found to accelerate contraction frequency in the embryonic heart and hindgut of Manduca in a dose-dependent fashion. Of these two possible targets, the hindgut proved to be more sensitive to CAP2, having a lower response threshold and a longer duration of response to a given concentration of the exogenously applied peptide. Based on these immunocytochemical, pharmacological and biochemical results, and on a previously published detailed analysis of Manduca embryogenesis, we conclude that CAP2 is probably released from a specific set of identified neurosecretory cells in the abdominal VNC to modulate embryonic gut activity at 75-80% of embryo development during ingestion of the extra-embryonic yolk.

Animals↗
PubMed1990

The embryonic development of larval muscles in Drosophila.

Each of the abdominal hemisegments A2-A7 in the Drosophila larva has a stereotyped pattern of 30 muscles. The pattern is complete by 13 h after egg laying, but the development of individual muscles has begun with the definition of precursors at least by the onset of germ band shortening, some 5.5 h earlier. The earliest signs of muscle differentiation are cell fusions, which occur in the ventralmost mesoderm overlying the CNS and at stereotyped positions in the rest of the mesoderm as the germ band shortens. At the end of shortening, the pattern of muscle precursors produced by these fusions is complete. Precursors filled with dye reveal extensive fine processes probably involved initially in cell fusion and, subsequently, in navigation over the epidermis to form attachment points. The muscle pattern is formed before innervation and without cell death. Thus, neither of these processes is involved in determining the distribution of precursors. Evidence is presented for the view that the development of the larval muscle pattern in Drosophila depends on a prior segregation of founder cells at appropriate locations in the mesoderm with which other cells fuse to form the precursors.

Animals↗
PubMed1988

Spatial and temporal patterns of neurogenesis in the central nervous system of Drosophila melanogaster.

Neurogenesis in the ventral CNS of Drosophila was studied using staining with toluidine blue and birth dating of cells monitored by incorporation of bromodeoxyuridine into DNA. The ventral CNS of the larva contains sets of neuronal stem cells (neuroblasts) which are thought to be persistent embryonic neuroblasts. Each thoracic neuromere has at least 47 of these stem cells whereas most abdominal neuromeres possess only 6. They occur in stereotyped locations so that the same neuroblast can be followed from animal to animal. The thoracic neuroblasts begin enlarging at 18-26 hr of larval life, DNA synthesis commences by 31-36 hr, and the first mitoses occur shortly thereafter. Mitotic activity continues through the remainder of larval life with the neuroblasts showing a minimum cell cycle time of less than 55 min during the late third larval instar. By 12 hr after pupariation each neuroblast has produced approximately 100 progeny which are collected with it into a discrete packet. The progeny accumulate in an immature, arrested state and only finish their differentiation into mature neurons with the onset of metamorphosis. Most of the abdominal neuroblasts differ from their thoracic counterparts in their minimum cell cycle time (less than 2 hr) and the duration of proliferation (from about 50 to 90 hr of larval life). Neurons produced during the larval stage account for more than 90% of the cells found in the ventral CNS of the adult.

Animals↗
PubMed1987

The expression of three members of the achaete-scute gene complex correlates with neuroblast segregation in Drosophila.

The expression of a subset of homologous genes of the AS-C is required during embryogenesis and metamorphosis for proper neural development. Here we study the expression of three of these genes (T3, T4, and T5) and show that their transcripts accumulate at the blastoderm stage in periodic patterns coincident with the dorsoventral extent of the neuroectoderm. Subsequent expression is in partially overlapping patterns that correlate with the segregation of neuroblasts. These genes are not transcribed in neurons. We also show that a deficiency for the AS-C prevents the appearance of at least one identified class of neuroblasts. We propose that the AS-C is part of a network of genes responsible for the segregation of neuroblasts.

Animals↗
PubMed1981

Embryonic development of identified neurons: segment-specific differences in the H cell homologues.

Although all of the segmental ganglia of the grasshopper come from identical sets of embryonic precursor cells, there are striking differences in the number and properties of the neurons in the mature ganglia. In every segment, midline precursor 3 (MP3) divides once and gives rise to two progeny. We describe the fate of the two MP3 progeny in different segments. The morphology, physiology, and survival of the MP3 progeny depend upon their segmental position in the embryo. In the meso- and metathoracic segments (T2 and T3), one of the two progeny of MP3 transforms into the H cell. In many of the abdominal segments, beginning with the fourth (A4), both MP3 progeny die. A gradient of transformation and cell death is seen in the intervening first three abdominal segments (A1 to A3). From A1 to A3, the MP3 progeny acquire fewer of the morphological phenotypes of the H cell. This is paralleled by the partial acquisition of the physiological phenotypes of the H cell. Thus, cells that are the progeny of the same precursor cell in different segments can either live or die and, if they survive, can develop different morphological and physiological properties.

Animals↗