Initiation Of Adult Development Research Articles

Morphogenetic mechanisms of coelom formation in the direct-developing sea urchin Heliocidaris erythrogramma

Indirect development via a feeding pluteus larva represents the ancestral mode of sea urchin development. However, some sea urchin species exhibit a derived form of development, called direct development, in which features of the feeding larva are replaced by accelerated development of the adult. A major difference between these two developmental modes is the timing of the formation of the left coelom and initiation of adult development. These processes occur much earlier in developmental and absolute time in direct developers and may be underlain by changes in morphogenetic processes. In this study, we explore whether differences in the cellular mechanisms responsible for the development of the left coelom and adult structures are associated with the change in the timing of their formation in the direct-developing sea urchin Heliocidaris erythrogramma. We present evidence that left coelom formation in H. erythrogramma, which differs in major aspects of coelom formation in indirect developers, is not a result of cell division. Further, we demonstrate that subsequent development of adult structures requires cell division.

Host‐parasite interactions between whiteflies and their parasitoids

There is relatively little information available concerning the physiological and biochemical interactions between whiteflies and their parasitoids. In this report, we describe interactions between aphelinid parasitoids and their aleyrodid hosts that we have observed in four host-parasite systems: Bemisia tabaci/Encarsia formosa, Trialeurodes vaporariorum/E. formosa, B. tabaci/Eretmocerus mundus, and T. lauri/Encarsia scapeata. In the absence of reported polydnavirus and teratocytes, these parasitoids probably inject and/or produce compounds that interfere with the host immune response and also manipulate host development to suit their own needs. In addition, parasitoids must coordinate their own development with that of their host. Although eggs are deposited under all four instars of B. tabaci, Eretmocerus larvae only penetrate 4th instar B. tabaci nymphs. A pre-penetrating E. mundus first instar was capable of inducing permanent developmental arrest in its host, and upon penetration stimulated its host to produce a capsule (epidermal in origin) in which the parasitoid larva developed. T. vaporariorum and B. tabaci parasitized by E. formosa initiated adult development, and, on occasion, produced abnormal adult wings and eyes. In these systems, the site of parasitoid oviposition depended on the host species, occurring within or pressing into the ventral ganglion in T. vaporariorum and at various locations in B. tabaci. E. formosa's final larval molt is cued by the initiation of adult development in its host. In the T. lauri-E. scapeata system, both the host whitefly and the female parasitoid diapause during most of the year, i.e., from June until the middle of February (T. lauri) or from May until the end of December (E. scapeata). It appears that the growth and development of the insects are directed by the appearance of new, young foliage on Arbutus andrachne, the host tree. When adult female parasitoids emerged in the spring, they laid unfertilized male-producing eggs in whiteflies containing a female parasitoid [autoparasitism (development of male larvae utilizing female parasitoid immatures for nutrition)]. Upon hatching, these male larvae did not diapause, but initiated development, and the adult males that emerged several weeks later mated with available females to produce the next generation of parasitoid females. Thus, the interactions that exist between whiteflies and their parasitoids are complex and can be quite diverse in the various host-parasitoid systems.

The extracellular matrix protein lacunin is expressed by a subset of hemocytes involved in basal lamina morphogenesis

The extracellular matrix protein of Manduca sexta known as lacunin is localized to basal laminae and granular cells of the hemolymph. Circulating granular cells increase in both number and size as pupal basal laminae break down after the initiation of adult development. Basal laminae of wing epithelia break down as ecdysteroid levels rise during adult development, and lacunin immunoreactivity concurrently passes from basal laminae to endocytic vacuoles of granular cells. Granular cells not only endocytose lacunin protein that they salvage from the remnants of the old basal laminae but they also express transcripts for lacunin. As new adult basal laminae form several days later, the number of circulating granular cells decreases as lacunin immunoreactivity appears in the new basal laminae.

Role of the brain and ring gland in regulation of pupal diapause in the flesh fly Sarcophaga crassipalpis

Larvae of Sarcophaga crassipalpis photoperiodically programmed for pupal diapause pupariate later than larvae programmed for continuous development. Pupariation time is determined by the brain-ring gland complex as evidenced by transplantation experiments in which the timing of pupariation was transferred from one larva to another by transplantation of the brain-ring gland complex. The developmental commitment (diapause or nondiapause) of the larva also can be transferred with the brain-ring gland complex if the recipient's own neuroendocrine system is suppressed by ring gland extirpation. Thus, photoperiodic programming of the brain-ring gland complex is not only responsible for developmental commitment but also for determining the duration of the prepupal period. Surgical experiments with pupae indicate that an intact brain-ring gland complex is required for diapause termination and initiation of adult development. Pupae fail to break diapause if either the brain or the ring gland is removed or if their nervous connections are severed.

Developmental changes in brain taurine levels during metamorphosis of the moth, Mamestra configurata Wlk.

Taurine in the brain of Mamestra configurata rose rapidly during the first half of metamorphosis until its amount and concentration were thirty fold and twenty fold higher than found in the pupa. Taurine levels then fell rapidly to the low amount and concentration found in the brain of the adult moth. The predominant source of increased brain taurine levels during the initiation of adult development was the blood as determined by quantitative radioisotope uptake experiments. Taurine was not taken up from the blood by the brains of pupae that had not completed ‘diapause development’, indicating a rigid compartmentalisation of taurine between the blood and brain during the prolonged period of ‘diapause development’. The change in the permeability of the brain to taurine from a state of apparent exclusion to one of rapid uptake may be an important event in the initiation of adult development. The highest levels of brain taurine were found during the period of intensive brain development, and especially during the development of the massive optic lobes which contained high concentrations of taurine. It is hypothesised that taurine, in addition to its neurochemical function in the ‘mature’ brains of the pupa and adult may have a special role in brain developmental processes per se.

Regulation of brain adenylate cyclase and the termination of silkmoth diapause

Factors which could account for increased levels of brain cycle AMP during the initiation of pupal-adult metamorphosis were examined in silkmoths. Cyclic nucleotide phosphodiesterase activity of whole brain homogenates was not depressed after the initiation of adult development. Adenylate cyclase activity was assayed in brain homogenates and in a partially purified membrane particle preparation. Parallel agonist and antagonist studies suggest that a substance with an active site resembling 5-hydroxytryptamine may be the natural activator of brain cyclase.

Abdominal production of ecdysterone and pupal-adult development in Tenebrio molitor (insecta, coleoptera)

Isolated abdomens of Tenebrio molitor of both sexes, ligated at pupal ecdysis, can undergo the adult molt because of their own production of the molting hormone (MH): A great peak in MH is detected by radioimmunoassay 6 to 10 days after ligation. Mass spectrometry indicates that MH consists principally of ecdysterone; small amounts of ecdysone are also detected. Our results indicate that hormonal concentrations in ligated abdomens are close to normal values in intact pupae and that the hormone is released into the hemolymph. The hormonal peak is clearly correlated with the initiation of adult development (apolysis and deposition of adult cuticle). Our data lead to the conclusion that this abdominal production of ecdysterone also occurs in nonligated animals and triggers pupal-adult development.

Levels of brain cyclic AMP and cyclic GMP during the initiation of adult development in the bertha armyworm, Mamestra configurata Wlk

Levels of brain cyclic AMP and cyclic GMP in Mamestra configurata remained essentially unchanged during the first three days of pharate adult development after pupae were transferred from eight months of cold storage at 5° to 20°C. Thereafter, cyclic AMP levels increased six-fold over a two week period from 0.22 pmole/brain to about 1.3 pmole/brain. Cyclic GMP levels doubled over the two week period, from 0.09 pmole/brain to about 0.19 pmole/brain. These changes appeared to follow the activation of brain neurosecretion rather than precede it. Brain cyclic AMP and cyclic GMP levels of non-developing pupae remained virtually unchanged at about 0.27 and 0.048 pmole/brain, respectively, following their transfer from two months of cold storage at 5° to 20°C. Cyclic AMP: cyclic GMP ratiosthus increase from about 2:1 in the pupal brain to 6:1 oreven 7:1 in the differentiating brain of the pharate adult. The results are consistent with an important role for cyclic AMP and cyclic GMP in brain processes that become established during differentiation of the adult brain, and perhaps in the case of cyclic AMP, in the differentiation process itself.

Cyclic nucleotides and nervous system function.

Cyclic nucleotides and nervous system function.

Brain cyclic AMP levels and the initiation of adult development in the Cecropia silkmoth

A six-fold increase in the level of brain cyclic AMP is observed in chilled Cecropia pharate adults within 24 hr of transfer from the cold to room temperature. This increase is not observed in pupae chilled for a period insufficient to allow initiation of adult development, nor after injury to diapausing pupae. Other tissues show a variable and minor response during initiation. Injected dibutyryl cAMP will cause initiation in insufficiently chilled pupae, but not in dauer pupae. The possible relationship of this rise in cAMP to the process of initiation is discussed.

Methylxanthine inhibition of neurosecretion in the brain and corpus cardiacum of Cecropia

The fine-structure of the median neurosecretory cells and corpora cardiaca of the Cecropia silkmoth during the first 7 days after transfer from cold conditions to room temperature was compared to that of similar animals whose development was arrested with aminophylline. The major difference observed was the failure of the intrinsic secretory cells of the corpus cardiacum to degenerate in the arrested animals. This failure to degenerate coincides with the expected period of brain hormone release. After long periods of arrest, the medial neurosecretory cells and their axons became distended with neurosecretory granules. The significance of these observations in the initiation of adult development is discussed.

The initiation of adult development in Sarcophaga argyrostoma by β-ecdysone

Sarcophaga argyrostoma pupae otherwise destined to diapause can be made to initiate prompt, complete adult development by injection of 0.2 to 0.3 μg β-ecdysone/g body weight, if the injection is given soon after head eversion at the time ecdysone levels would normally increase in developing animals. At these doses some animals show only the earliest signs of adult development and then enter diapause. After two weeks in diapause, a 40-fold higher dose (10 μg/g) is required to initiate development promptly. β-ecdysone can also accelerate the termination of diapause after a time delay which is dose-dependent. Doses of 6 to 10 μg/g lead to hyperhormonal abnormalities affecting antennae, genitalia, and bristle orientation.

Electron microscopic study of changes in the subcellular organization during metamorphosis of the fat-body cell of Philosamia cynthia ricini (Lepidoptera)

Electron microscopic observations were made on the fat-body cells of Philosamia cynthia ricini during the development from the early fifth instar to the early stage of adult development. The cells of the young fifth-instar larva possess numerous mitochondria and ribosomes, an endoplasmic reticulum and a Golgi complex. Fat droplets are the only cytoplasmic inclusion which is structurally recognized. About 1 day before the larva matures, glycogen-rich granules begin to appear. During the spinning stage, a drastic disappearance of the cytoplasmic organelles occurs. When larvae finish spinning, most of the cytoplasm becomes filled with such inclusions as fat droplets, glycogen-rich granules, and “dark bodies”. Mitochondria and ribosomes in much decreased numbers are left as well-identifiable cytoplasmic organelles. This condition of the cells, attained at the spinning stage, remains unchanged until the initiation of adult development, when the mitochondria and ribosomes increase in number and the endoplasmic reticulum again develops. Subsequently, the “intercellular matrix” covering the cell surface loses its compact texture, and finally the cell itself disintegrates to liberate its contents into the blood. Remarkable changes in the nuclear morphology which occur during development are described.

PHYSIOLOGY OF INSECT DIAPAUSE. V. ASSAY OF THE GROWTH AND DIFFERENTIATION HORMONE OF LEPIDOPTERA BY THE METHOD OF TISSUE CULTURE

1. Spermatogonia and spermatocytes isolated from the testes of dormant pupae of the silkworms, Platysamia cecropia and Samia walkeri (Cynthia), promptly develop into well differentiated spermatids when cultured in hanging-drops of blood obtained from pupating larvae or developing adults of these species. Comparable development does not occur in cultures prepared in blood obtained from diapausing pupae or from mature larvae prior to a well-defined period before the onset of the prepupal stage.2. The in vitro development of the sex cells signals the presence of a growth-promoting hormone. In inactive blood, as during the pupal diapause, this hormone is ordinarily in sub-threshold titer.3. In addition to promoting the maturation of spermatocytes, the hormone causes the in vitro multiplication of blood cells and spermatogonia.4. Pupal blood is active in promoting the development of germ cells in vitro after the initiation of adult development; the blood of mature larvae becomes active at a stage signalled by the spinning of the inner coat of the cocoon. This timing corresponds precisely with the periods during which the prothoracic glands secrete the growth and differentiation hormone which provokes the pupation of the larvae and the adult development of the pupa.5. Evidence is presented that the development of the germ cells in vitro reflects the presence in the culture medium of the growth and differentiation hormone secreted by the prothoracic glands. The development of the sex cells in the tissue culture appears to be an exceptionally sensitive test for this hormone.6. By the use of this test the hormone was found to be non-dialyzable and destroyed or precipitated by exposure to temperatures higher than 75° C. Accordingly, it is concluded that the growth and differentiation hormone is either a protein or a smaller molecule conjugated to a protein.