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Biomedical subjects

R Booker

Publications and source records attributed to R Booker.

At least 19 recordsLinked to original sources
PubMed2001

Host recognition by the tobacco hornworm is mediated by a host plant compound.

It is generally believed that animals make decisions about the selection of mates, kin or food on the basis of pre-constructed recognition templates. These templates can be innate or acquired through experience. An example of an acquired template is the feeding preference exhibited by larvae of the moth, Manduca sexta. Naive hatchlings will feed and grow successfully on many different plants or artificial diets, but once they have fed on a natural host they become specialist feeders. Here we show that the induced feeding preference of M. sexta involves the formation of a template to a steroidal glycoside, indioside D, that is present in solanaceous foliage. This compound is both necessary and sufficient to maintain the induced feeding preference. The induction of host plant specificity is at least partly due to a tuning of taste receptors to indioside D. The taste receptors of larvae fed on host plants show an enhanced response to indioside D as compared with other plant compounds tested.

Animals↗
PubMed2001

The role of Ultrabithorax in the patterning of adult thoracic muscles in Drosophila melanogaster.

Mutations in the homeotic gene, Ultrabithorax (Ubx), result in the transformation of the third thoracic (T3) segment into the second thoracic (T2) segment. Although it has been well established that these mutations have striking effects on adult epidermal structures in T3, the effect of these mutations on the adult musculature has been controversial. In this study, a series of Ubx regulatory mutations, anterobithorax, bithorax, postbithorax, and bithoraxoid, as well as combinations of these alleles were used to reevaluate the role of Ubx in the patterning of the T3 musculature. Homeotic indirect and direct flight muscles (IFMs and DFMs) were identified in the transformed T3 segment of all alleles and allelic combinations with the exception of postbithorax. We critically evaluated the pattern and amount of these muscles and found that while the amount and/or quality of homeotic IFMs increased, the amount of homeotic DFMs did not vary significantly as the severity of the ectodermal transformation increased. Because Ubx is not expressed in the adult mesoderm of T3, these results suggest that inductive cues play a major role in the patterning of adult thoracic muscles. We provide a model that illustrates the central role of inductive cues in generating the final adult muscle pattern in the thorax.

Alleles↗
PubMed2000

Imaginal pioneers prefigure the formation of adult thoracic muscles in Drosophila melanogaster.

In insects, specialized mesodermal cells serve as templates to organize myoblasts into distinct muscle fibers during embryogenesis. In the grasshopper embryo, large mesodermal cells called muscle pioneers extend between the epidermal attachment points of future muscle fibers and serve as foci for myoblast fusion. In the Drosophila embryo, muscle founder cells serve a similar function, organizing large numbers of myoblasts into larval muscles. During the metamorphosis of Drosophila, nearly all larval muscles degenerate and are replaced by a set of de novo adult muscles. The extent to which specialized mesodermal cells homologous to the founders and pioneers of the insect embryo are involved in the development of adult-specific muscles has yet to be established. In the larval thorax, the majority of imaginal myoblasts are associated with the imaginal discs. We report here the identification of a morphologically distinct class of disc-associated myoblasts, which we call imaginal pioneers, that prefigures the formation of at least three adult-specific muscles, the tergal depressor of the trochanter and dorsoventral muscles I and II. Like the muscle pioneers of the grasshopper, the imaginal pioneers attach to the epidermis at sites where the future muscle insertions will arise and erect a scaffold for developing adult muscles. These findings suggest that a prior segregation of imaginal myoblasts into at least two populations, one of which may act as pioneers or founders, must occur during development.

Animals↗
PubMed2000

Octopamine mimics the effects of parasitism on the foregut of the tobacco hornworm Manduca sexta.

The parasitic braconid wasp Cotesia congregata lays its eggs inside the body of the larval stage of its host, the moth Manduca sexta. The Cotesia congregata larvae develop within the hemocoel of their host until their third instar, when they emerge and spin cocoons and pupate on the outer surface of the caterpillar. From this time until their death approximately 2 weeks later, the Manduca sexta larvae show striking behavioral changes that include dramatic declines in spontaneous activity and in the time spent feeding. Coincident with these behavioral changes, it is known that octopamine titers in the hemolymph of the host become elevated by approximately 6.5-fold. Octopamine is an important modulator of neural function and behavior in insects, so we examined hosts for neural correlates to the behavioral changes that occur at parasite emergence. We found that, in addition to the changes reported earlier, after parasite emergence (post-emergence), Manduca sexta larvae also showed marked deficits in their ability to ingest food because of a disruption in the function of the frontal ganglion that results in a significant slowing or the absence of peristaltic activity in the foregut. This effect could be produced in unparasitized fifth-instar larvae by application of blood from post-emergence parasitized larvae or of 10(-6)mol l(-1)d,l-octopamine (approximately the level in the hemolymph of post-emergence larvae). In contrast, blood from parasitized larvae before their parasites emerge or from unparasitized fifth-instar larvae typically had no effect on foregut activity. The effects of either post-emergence parasitized blood or 10(-6)mol l(-1) octopamine could be blocked by the octopamine antagonists phentolamine (at 10(-5)mol l(-1)) or mianserin (at 10(-7)mol l(-1)).

Animals↗
PubMed1999

Homeotic gene expression in the wild-type and a homeotic mutant of the moth Manduca sexta.

Antibodies were used to examine the expression patterns of Antennapedia (Antp), Ultrabithorax (Ubx), Ubx and abdominal-A combined (Ubx/abd-A), and Distalless (Dll) in the embryos of the moth Manduca sexta. We found that the spatial and temporal pattern of Antp expression in Manduca was correlated with the anterior migration of two patches of epithelium that include the anterior-most tracheal pits, and with the development of functional spiracles. Ubx expression showed an intricate pattern which suggests complex regulation during development. Throughout Manduca embryogenesis the expression of Ubx/Abd-A and Dll was similar to that reported for other insects. However, there was no apparent reduction in Ubx/Abd-A expression in the Manduca abdominal proleg primordia that expressed Dll. The expression of these four proteins was also examined in embryos of the Manduca homozygous homeotic mutant Octopod (Octo). The Octo mutation results in the transformation of A1 and A2 in the anterior direction, with homeotic legs appearing on A1 and occasionally A2. Our results suggest that in Octo animals there is a reduction in the level of Ubx protein expression throughout its domain. Based on homeotic gene expression in wild-type and mutant Manduca and in other insects, we discuss potential roles of homeotic genes in insect morphological evolution.

Amino Acid Sequence↗
PubMed1998

Innervation regulates the metamorphic fates of larval abdominal muscles in the moth, Manduca sexta.

With the onset of metamorphosis, the abdominal muscles of the moth, Manduca sexta, follow one of three developmental fates: maintenance, respecification, or death. The maintained muscles retain their larval size and morphology throughout adult development. The respecified and dying muscles dedifferentiate, which involves regression, nuclear degeneration, and myofibril breakdown. Nuclei in both dying and respecified muscles also proliferate. The amount of nuclear degeneration is greater in the dying muscle fibers, and the amount of nuclear proliferation is greater in the respecified muscles. Four to ten days after pupation, the sizes of the respecified muscles stabilize while the dying muscles are lost. During regression, a subset of the respecified muscle fibers die. The surviving respecified muscle fibers grow and differentiate during the last half of adult development. In respecified muscles, denervation triggers an increased amount of nuclear degeneration and a decreased amount of nuclear proliferation. As a result, denervated respecified fibers experience increased muscle regression including an increased loss of muscle fibers and sometimes muscle death. Surviving respecified fibers still grow and differentiate yet are only 5 to 12% of the control size. Denervation triggers dedifferentiation in maintained muscles, resulting in fiber loss and occasionally muscle death. The percentage of fibers which dedifferentiate varies between different muscles. Denervation also triggers nuclear proliferation, with the amount of nuclear proliferation correlated with the extent of dedifferentiation of the individual muscle fibers. The dedifferentiated maintained fibers subsequently undergo differentiation in the absence of muscle growth.

Abdominal Muscles↗
PubMed1998

The role of the frontal ganglion in the feeding and eclosion behavior of the moth manduca sexta

We have examined the musculature and motor patterns of the foregut and the role of the frontal ganglion in the adult moth Manduca sexta. During adult development, the structure of the foregut changes from a simple straight tube to a pump consisting of a flexible-roofed chamber or cibarium, with dilator muscles that raise the roof to draw in fluids and a compressor to push it down and force the fluid down the thin-walled esophagus. The frontal ganglion drives the activity of this cibarial pump during feeding, which is triggered by the application of sucrose solution or water to the proboscis. The feeding motor pattern consists of coupled bursts of the pump dilators and shorter-duration, high-frequency bursts of spikes from the pump compressor. The pump is also activated at the adult molt. At this time, it is used both before the moth emerges from the pupal case for swallowing molting fluid and again after emergence for swallowing air. These behaviors are important for eclosion and are necessary for the expansion of the wings after eclosion. Their motor patterns are similar to the feeding program. Up to 24 h before adult ecdysis, this motor pattern can be triggered by the peptide eclosion hormone. The other eclosion-related peptide, Manduca sexta eclosion-triggering hormone, does not appear to trigger activity of the cibarial pump.

Journal Article↗
PubMed1997

Asthma inhalers.

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Asthma↗
PubMed1996

Genesis of the adult retina and outer optic lobes of the moth, Manduca sexta. I. patterns of proliferation and cell death.

We have examined the development of the adult retina and the outer optic lobes in the moth Manduca sexta. The adult retina is generated from a group of epithelial cells lying within the larval head capsule between the larval ocelli and antenna. Proliferation of these cells begins during the feeding larval stage but accelerates at the end of the final larval instar. Proliferation occurs in two zones of mitotic activity; these zones flank a furrow in the presumptive retinal epithelium. The furrow and flanking mitotic zones migrate from posterior to anterior across the presumptive retinal epithelium. Posterior to the furrow, presumptive retinal cells from clusters and extend axons into the larval optic nerve. We have also examined the temporal patterns of neuronal proliferation and cell death during genesis of the adult outer optic ganglia, the medulla and the lamina. The medulla and the lamina are generated by distinct populations of neuroblasts in the outer optic analage; the neuroblasts divide asymmetrically to generate ganglion mother cells. Ganglion mother cells later divide symmetrically to generate immature neurons. Generation of the medulla cortex starts with the onset of the final larval instar, and cell death within the medulla cortex begins after the end of the final larval instar. Generation of the lamina cortex is initiated with the arrival of retinal afferents at the optic lobes, and cell death in the lamina cortex begins 1 day later. Generation of the outer optic ganglia terminates with the abrupt cessation of mitotic activity followed by degeneration of the outer optic anlage.

Animals↗
PubMed1996

Genesis of the adult retina and outer optic lobes of the moth, Manduca sexta. II. Effects of deafferentation and developmental hormone manipulation.

We have examined factors affecting neuronal proliferation and cell death during development of the adult outer optic ganglia in the moth Manduca sexta. The role of retinal afferents was addressed by optic nerve section on the first day of pupation, when the retina is only partially formed. Deafferentation by optic nerve section resulted in increased levels of cell death in the medulla cortex but did not affect medulla precursor proliferation. Conversely, division of lamina ganglion mother cells ceased following deafferentation, whereas cell death in the lamina cortex did not increase significantly. Implantation of isolated outer optic anlage into host animals demonstrated that medulla precursor proliferation was independent of centripetal inputs and retinal afferents. The role of developmental hormones in regulating outer optic ganglia development was also investigated. Many events in medulla and lamina development are correlated with changes in the titers of the ecdysteroids, and these events could be prevented by application of a juvenile hormone mimic (JHM). Application of JHM early in the fifth (final) larval instar terminated medulla precursor proliferation and prevented the initiation of lamina precursor proliferation, but application late in the fifth instar (after the commitment peak of ecdysteroids) had little effect on proliferation. Application of JHM on the third or fourth day of pupal life prolonged precursor proliferation and delayed degeneration of the outer optic anlage. Precocious application of 20-hydroxyecdysone on the first day of pupal life accelerated outer optic anlage degeneration but did not cause premature termination of proliferation.

Afferent Pathways↗
PubMed1996

Postembryonic neurogenesis in the central nervous system of the tobacco hornworm, Manduca sexta. III. Spatial and temporal patterns of proliferation.

Postembryonic neurogenesis leads to a dramatic increase in the number of functional neurons within the segmental ganglia of the moth, Manduca sexta. These adult-specific neurons are generated during larval life by segment-specific arrays of individually identifiable stem cells, or neuroblasts (Nbs). By the end of the feeding larval stage, each Nb has generated a discrete nest of progeny, which ranges in size from less than 10 to more than 70 progeny. The sizes of these identifiable nests of progeny vary in a segment-specific manner, with the thoracic nests containing a greater number of progeny compared with their homologues in the simpler abdominal ganglia. In order to describe those factors that influence the size of the post-embryonic neuronal lineages, we examined the spatial and temporal pattern of postembryonic neurogenesis in the segmental ganglia of Manduca. The rates at which the identifiable nests accumulated progeny were estimated by counting the number of progeny within the nests, using sectioned material isolated from animals at stages ranging from embryonic hatching until the end of the feeding larval stage. All of the postembryonic Nbs began to generate progeny at around the time of the molt to the third larval instar. Each nest added progeny at a rate that was a characteristic of its identity and segment of origin. Although all of the nests within the thorax continued to accumulate progeny throughout the feeding larval stage, several of the abdominal nests showed little or no growth following the molt to the fifth larval instar. The thymidine analog 5-bromo 2-deoxyuridine (5-BrdU) was used to estimate the mitotic rates of the identifiable Nbs. The number of labeled progeny within a nest 24 h after application of 5-BrdU ranged from a low of 1 to 2 to a high of 11 to 13 labeled cells. In some instances there was a good correlation between the estimated mitotic rate of an identified Nb and the rate of growth of its associated nest of progeny. However, several of the identifiable nests accumulated progeny at a slower rate than predicted based on the estimated mitotic rate of the Nb. Cell death appears to be responsible for slowing the growth of the nests during the feeding larval stage. We estimate that 10% to 70% of the neurons generated during the feeding larval stage degenerate within 24 h of their birth. The level of cell death observed within a nest was dependent on both its identity and its segment of origin.

Animals↗