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V Hartenstein

Publications and source records attributed to V Hartenstein.

50 records · Page 3Linked to original sources
PubMed1993

Early pattern of neuronal differentiation in the Xenopus embryonic brainstem and spinal cord.

Wholemount antibody labeling techniques and horseradish peroxidase backfilling were used to analyze the pattern of neuronal differentiation in the embryonic Xenopus central nervous system between stages 22 and 35/36. In the spinal cord, the first neurons to differentiate are the Rohon-Beard neurons; they are followed by ventral neurons with descending axons (descending interneurons, motoneurons) and lateral interneurons with commissural axons. The somata and axons of these primary neurons form dorsal, ventral, and lateral columns, respectively; the ventral and lateral columns uninterruptedly continue forward into the brainstem. The distribution and projection patterns of spinal neurons were analyzed quantitatively. Rohon-Beard neurons, commissural interneurons, and primary motoneurons vary in number from segment to segment. Thus, these neurons are not distributed in a segmental pattern. In each segment, neurons of a given type project axons whose length varies over a wide range. The numerical distribution of axons formed by a population of neurons of a given type was calculated and expressed as the projection profile of these neurons. For each type of neuron and spinal segment, the projection profile is different. Furthermore, the projection profiles change in a systematic way along the spinal cord. For example, the fraction of Rohon-Beard neurons with long ascending axons steadily increases if one moves towards caudal spinal levels. The findings suggest that suprasegmental cues with a graded distribution along the spinal cord determine the number and projection profile of a particular cell type in a given segment.

Animals↗
PubMed1993

Development of the taste bristles on the labellum of Drosophila melanogaster.

The taste bristles of the adult labellum develop from the labial discs within the first 30 hr of pupation. The neuron-specific antibody Mab22C10 and the tissue-specific beta-galactosidase activity in the A37 strain were used as cell markers for the developing sensilla. These experiments revealed that the sensory progenitors of all the labellar bristles are specified in three waves occurring 0, 6, and 16 hr after pupation. The incorporation of the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) into the cells of the developing proboscis further supports the temporal pattern of the sensillum specification. Mitotic activity in the bristles specified in the first wave is completed before the next wave is initiated. The eight cells that constitute a single bristle share a common lineage. The trichogen and tormogen cells are siblings from a single progenitor and the thecogen and the five neurons share a common ancestry. Our results provide a basis for the identification of molecules that specify the development of the polyinnervated bristles of the adult and the specification of neurons with different stimulus specificities.

Age Factors↗
PubMed1993

The role of the tracheae and musculature during pathfinding of Drosophila embryonic sensory axons.

Developing sensory axons were studied in Drosophila embryos which carried a mutation in the trachealess and/or the twist gene. In these embryos, the tracheae and/or somatic muscles, which represent part of the substrate on which sensory axons normally grow, are absent. The results demonstrate that in each of these three mutant backgrounds, the majority of sensory nerves form normally. This indicates that neither the tracheae nor the somatic musculature is absolutely required for pathfinding of the embryonic sensory axons. On the other hand, the incidence of misrouted axons is significantly increased, most strongly in the trh, twi double mutant. Furthermore, axonal elongation is considerably slowed down, and sensory neurons which fail to send out an axon are frequent. We take our results to indicate that peripheral axons in the Drosophila embryo may be guided by multiple cues which, acting together, ensure the high fidelity of axonal pathways observed in normal development. The removal of one of these cues by itself does not necessarily lead to the total disability of axons to reach their target, although it enhances the frequency of error in pathfinding.

Animals↗
PubMed1993

The embryonic development of the Drosophila visual system.

We have used electron-microscopic studies, bromodeoxyuridine (BrdU) incorporation and antibody labeling to characterize the development of the Drosophila larval photoreceptor (or Bolwig's) organ and the optic lobe, and have investigated the role of Notch in the development of both. The optic lobe and Bolwig's organ develop by invagination from the posterior procephalic region. After cells in this region undergo four postblastoderm divisions, a total of approximately 85 cells invaginate. The optic lobe invagination loses contact with the outer surface of the embryo and forms an epithelial vesicle attached to the brain. Bolwig's organ arises from the ventralmost portion of the optic lobe invagination, but does not become incorporated in the optic lobe; instead, its 12 cells remain in the head epidermis until late in embryogenesis when they move in conjunction with head involution to reach their final position alongside the pharynx. Early, before head involution, the cells of Bolwig's organ form a superficial group of 7 cells arranged in a 'rosette' pattern and a deep group of 5 cells. Later, all neurons move out of the surface epithelium. Unlike adult photoreceptors, they do not form rhabdomeres; instead, they produce multiple, branched processes, which presumably carry the photopigment. Notch is essential for two aspects of the early development of the visual system. First, it delimits the number of cells incorporated into Bolwig's organ. Second, it is required for the maintenance of the epithelial character of the optic lobe cells during and after its invagination.

Animals↗
PubMed1992

The function of the neurogenic genes during epithelial development in the Drosophila embryo.

The complex embryonic phenotype of the six neurogenic mutations Notch, mastermind, big brain, Delta, Enhancer of split and neuralized was analyzed by using different antibodies and PlacZ markers, which allowed us to label most of the known embryonic tissues. Our results demonstrate that all of the neurogenic mutants show abnormalities in many different organs derived from all three germ layers. Defects caused by the neurogenic mutations in ectodermally derived tissues fell into two categories. First, all cell types that delaminate from the ectoderm (neuroblasts, sensory neurons, peripheral glia cells and oenocytes) are increased in number. Secondly, ectodermal tissues that in the wild type form epithelial structures lose their epithelial phenotype and dissociate (optic lobe, stomatogastric nervous system) or show significant differentiative abnormalities (trachea, Malpighian tubules and salivary gland). Abnormalities in tissues derived from the mesoderm were observed in all six neurogenic mutations. Most importantly, somatic myoblasts do not fuse and/or form an aberrant muscle pattern. Cardioblasts (which form the embryonic heart) are increased in number and show differentiative abnormalities; other mesodermal cell types (fat body, pericardial cells) are significantly decreased. The development of the endoderm (midgut rudiments) is disrupted in most of the neurogenic mutations (Notch, Delta, Enhancer of split and neuralized) during at least two stages. Defects occur as early as during gastrulation when the invaginating midgut rudiments prematurely lose their epithelial characteristics. Later, the transition of the midgut rudiments to form the midgut epithelium does not occur. In addition, the number of adult midgut precursor cells that segregate from the midgut rudiments is strongly increased. We propose that, at least in the ectodermally and endodermally derived tissues, neurogenic gene function is primarily involved in interactions among cells that need to acquire or to maintain an epithelial phenotype.

Animals↗
PubMed1991

Neuronal determination without cell division in Xenopus embryos.

Cell division in the Xenopus CNS was blocked by incubating embryos in a mixture of the DNA synthesis inhibitors hydroxyurea and aphidicolin. Surprisingly, embryos treated at the beginning of gastrulation proceeded normally through neurulation, neural tube closure, and CNS subdivision. Thus, cell division is not critical for neural induction or early morphogenetic events in the CNS. Neuroblasts in treated embryos differentiated into neurons of many classes, indicating that cellular determination in the CNS can be dissociated from lineage and birth date. Axonal tracts and embryonic reflexes also developed. The remarkable amount of normal CNS development that occurs in these animals may be explained by a series of sequential inductions that are largely independent of cell proliferation.

Animals↗
PubMed1991

Hairless is required for the development of adult sensory organ precursor cells in Drosophila.

Reduction of the wild-type activity of the gene Hairless (H) results in two major phenotypic effects on the mechanosensory bristles of adult Drosophila. Bristles are either 'lost' (i.e. the shaft and socket fail to appear) or they exhibit a 'double socket' phenotype, in which the shaft is apparently transformed into a second socket. Analysis of the phenotypes conferred by a series of H mutant genotypes demonstrates (1) that different sensilla exhibit different patterns of response to decreasing levels of H+ function, and (2) that the 'bristle loss' phenotype results from greater loss of H+ function than the 'double socket' phenotype. The systematic study of H allelic combinations enabled us to identify genotypes that reliably produce specific mutant defects in particular positions on the bodies of adult flies. This permitted us to investigate the cellular development of sensilla in these same positions in larvae and pupae and thereby establish the developmental basis for the mutant phenotypes. We have found that H is required for at least two steps of adult sensillum development. In positions where 'double socket' microchaetes appear on the notum of H mutant flies, sensillum precursor cells are present in the developing pupa and divide normally, but their progeny adopt an aberrant spatial arrangement and fail to differentiate correctly. In regions of the notum exhibiting 'bristle loss' in adult H mutants, we were unable at the appropriate stages of development to detect sensillum-specific cell types, the precursor cell divisions that generate them, or the primary precursor cells themselves. Thus, the H 'bristle loss' phenotype appears to reflect a very early defect in sensillum development, namely the failure to specify and/or execute the sensory organ precursor cell fate. This finding indicates that H is one of a small number of identified genes for which the loss-of-function phenotype is the failure of sensillum precursor cell development.

Alleles↗
PubMed1990

A dual function of the Notch gene in Drosophila sensillum development.

We have investigated the function of the neurogenic gene Notch (N) during development of the adult sensilla of Drosophila. Heat pulses were applied to flies carrying the temperature-sensitive Notch allele Nts1 at different larval and pupal stages. We can show that the reduction of Notch+ function during a short interval prior to the onset of sensillum precursor division, resulting from a heat pulse between 0 and 14 hr after puparium formation (apf), leads to an increase in microchaete precursors at the expense of epidermal cells. The structure and cellular composition of the sensilla produced by these supernumerary precursors are normal. Later heat pulses which include the interval immediately after sensillum precursor division (14-20 hr apf) lead, among the progeny of the sensillum precursors, to a hyperplasia of sensory neurons, at the expense of accessory cells. The resulting "sensilla" consist of neurons only and lack the external cuticular structures (i.e., shaft, socket). These results demonstrate that similar mechanisms both of which involve the function of the Notch gene may be operating to sort out (premitotic) sensillum precursors from epidermal precursors and (postmitotic) sensory neurons from accessory cells. They further show that in postmitotic sensillum cells the differentiative fate is not yet irreversibly fixed, but presumably requires cell-cell interaction to become established.

Alleles↗
PubMed1990

Sensillum development in the absence of cell division: the sensillum phenotype of the Drosophila mutant string.

We have investigated sensillum development in Drosophila embryos homozygous for mutations in the locus string (stg). In these embryos, cell division is blocked following blastoderm formation. This permits a study of the differentiative fate of undivided precursor cells, in particular those giving rise to the larval sensory organs (sensilla). Of the different cell fates normally represented in the sensilla (i.e., sensory neuron, thecogen cell, trichogen cell, tormogen cell, glia cell), only the phenotype of sensory neurons is expressed morphologically in stg embryos, suggesting that the neuronal fate predominates over the fates of the nonneuronal accessory cells. Consistent with this finding, the P element-lacZ insertion A1-2nd-29, which is a marker for trichogen and tormogen cells in the wild-type embryo, is not expressed in the body wall of the stg embryo. Some sensillum precursor cells appear to express a mixed fate in stg mutants: They express antigens (recognized by the monoclonal antibodies 22C10 and 21A6) which in the wild-type appear in separate cells (sensory neurons and thecogen cell, respectively). The differentiation of undivided cells in stg embryos is not restricted to the peripheral nervous system; in all types of tissues analyzed in this study (e.g., epidermis, intestine, muscle, CNS), precursor cells express characteristics normally exhibited by their progeny.

Animals↗
PubMed1989

Early neurogenesis in Xenopus: the spatio-temporal pattern of proliferation and cell lineages in the embryonic spinal cord.

Lineage tracing techniques and pulse labeling experiments were used to reveal the lineages and the pattern of proliferation of neural precursors in the Xenopus neural plate. After gastrulation there is a wave of mitosis; most cells of the neural plate undergo a single division during this wave. After this first division, many cells leave the cell cycle and differentiate as primary neurons. In the stage 35/36 hatching larvae, clones of primary neurons usually contain only two cells. The remainder, most of which arise from the superficial layer, are predominantly the precursors of secondary neurons. They are mitotically quiescent until stage 20, and then undergo another one to two rounds of division during embryonic life. Secondary precursors and primary neurons are never part of the same clone, although, in individual clones, primary neurons are frequently of different types. By the neural plate stage, separate precursors seem to exist for primary and secondary neurons, but the precursors of primary neurons themselves are pluripotent.

Animals↗
PubMed1989

Development of adult sensilla on the wing and notum of Drosophila melanogaster.

We have investigated the temporal pattern of appearance, cell lineage, and cytodifferentiation of selected sensory organs (sensilla) of adult Drosophila. This analysis was facilitated by the discovery that the monoclonal antibody 22C10 labels not only the neuron of the developing sensillum organ, but the accessory cells as well. The precursors of the macrochaetes and the recurved (chemosensory) bristles of the wing margin divide around and shortly after puparium formation, while those of the microchaetes and the stout and slender (mechanosensory) bristles of the wing margin divide between 9 h and 18 h after puparium formation (apf). The onset of sensillum differentiation follows the terminal precursor division within a few hours. Four of the cells in an individual microchaete organ are clonally related: A single first-order precursor cell divides to produce two second-order precursors; one of these divides into the neuron and thecogen cell, the other into the trichogen cell and tormogen cell. Along the anterior wing margin, two rounds of division generate the cells of the mechanosensory sensilla; here, no strict clonal relationship seems to exist between the cells of an individual sensillum. At the time of sensillum precursor division, many other, non-sensillum-producing cells within the notum and wing proliferate as well. This mitotic activity follows a spatially non-random pattern.

Animals↗
PubMed1983

Basal telencephalic origins of the anterior commissure of the rat.

The cells of origin of the three limbs of the rat's anterior commissure (AC) have been identified by horseradish peroxidase histochemistry. Following transection of the corpus callosum and hippocampal commissure, rats were subjected to multiple, unilateral injections of horseradish peroxidase throughout one cerebral hemisphere. The cells of origin of the rat's AC are found in the anterior olfactory nucleus, the olfactory tubercles, the anterior piriform cortex, the nucleus of the lateral olfactory tract, the lateral, basolateral, basomedial and cortical nuclei of the amygdala, the posterior perirhinal cortex, and the entorhinal cortex. Anterogradely labeled fibers were also found in the olfactory bulbs and in the plexiform layer of the anterior and posterior piriform cortices.

Amygdala↗
PubMed1981

The arborization of single callosal axons in the mouse cerebral cortex.

After several large cortical injections of horseradish peroxidase, individual callosal axons could be observed in most cortical areas contralateral to the injected hemisphere. They left the white matter and travelled for various distances (up to 2 mm) deep in layer VI, then turned to penetrate the cortex radially or obliquely, giving collaterals to several layers and forming narrow terminal arborisations in supragranular layers. In addition, callosal fibers were seen predominantly in deep cortical layers, which fibers could be interpreted either as collaterals of the thick fibers or as a distinct class of callosal afferents.

Afferent Pathways↗