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PubMed2006

From embryo to adult--beyond the conventional periodization of arthropod development.

The traditional framework for the description of arthropod development takes the molt-to-molt interval as the fundamental unit of periodization, which is similar to the morphological picture of the main body axis as a series of segments. Developmental time is described as the subdivision into a few major stages of one or more instars each, which is similar to the subdivision of the main body axis into regions of one to many segments each. Parallel to recent criticisms to the segment as the fundamental building block of arthropod anatomy, we argue that, while a firm subdivision of development in stages is useful for describing arthropod ontogeny, this is limiting as a starting point for studying its evolution. Evolutionary change affects the association between different developmental processes, some of which are continuous in time whereas others are linked to the molting cycle. Events occurring but once in life (hatching; first achieving sexual maturity) are traditionally used to establish boundaries between major units of arthropod developmental time, but these boundaries are quite labile. The presence of embryonic molts, the 'gray zone' of development accompanying hatching (with the frequent delivery of an immature whose qualification as 'free-embryo' or ordinary postembryonic stage is arbitrary), and the frequent decoupling of growth and molting suggest a different view. Beyond the simple comparison of developmental schedules in terms of heterochrony, the flexible canvas we suggest for the analysis of arthropod development opens new vistas into its evolution. Examples are provided as to the origin of holometaboly and hypermetaboly within the insects.

Animals↗
PubMed2000

Evidence for a G protein-coupled gamma-hydroxybutyric acid receptor.

gamma-Hydroxybutyric acid (GHB) is a naturally occurring metabolite of GABA that has been postulated to exert ubiquitous neuropharmacological effects through GABA(B) receptor (GABA(B)R)-mediated mechanisms. The alternative hypothesis that GHB acts via a GHB-specific, G protein-coupled presynaptic receptor that is different from the GABA(B)R was tested. The effect of GHB on regional and subcellular brain adenylyl cyclase in adult and developing rats was determined and compared with that of the GABA(B)R agonist (-)-baclofen. Also, using guanosine 5'-O:-(3-[(35)S]thiotriphosphate) ([(35)S]GTPgammaS) binding and low-K:(m) GTPase activity as markers the effects of GHB and (-)-baclofen on G protein activity in the brain were determined. Neither GHB nor baclofen had an effect on basal cyclic AMP (cAMP) levels. GHB significantly decreased forskolin-stimulated cAMP levels by 40-50% in cortex and hippocampus but not thalamus or cerebellum, whereas (-)-baclofen had an effect throughout the brain. The effect of GHB on adenylyl cyclase was observed in presynaptic and not postsynaptic subcellular tissue preparations, but the effect of baclofen was observed in both subcellular preparations. The GHB-induced alteration in forskolin-induced cAMP formation was blocked by a specific GHB antagonist but not a specific GABA(B)R antagonist. The (-)-baclofen-induced alteration in forskolin-induced cAMP formation was blocked by a specific GABA(B)R antagonist but not a specific GHB antagonist. The negative coupling of GHB to adenylyl cyclase appeared at postnatal day 21, a developmental time point that is concordant with the developmental appearance of [(3)H]GHB binding in cerebral cortex, but the effects of (-)-baclofen were present by postnatal day 14. GHB and baclofen both stimulated [(35)S]GTPgammaS binding and low-K:(m) GTPase activity by 40-50%. The GHB-induced effect was blocked by GHB antagonists but not by GABA(B)R antagonists and was seen only in cortex and hippocampus. The (-)-baclofen-induced effect was blocked by GABA(B)R antagonists but not by GHB antagonists and was observed throughout the brain. These data support the hypothesis that GHB induces a G protein-mediated decrease in adenylyl cyclase via a GHB-specific G protein-coupled presynaptic receptor that is different from the GABA(B)R.

Adenylyl Cyclases↗
PubMed1986

Delimiting regulatory sequences of the Drosophila melanogaster Ddc gene.

We delimited sequences necessary for in vivo expression of the Drosophila melanogaster dopa decarboxylase gene Ddc. The expression of in vitro-altered genes was assayed following germ line integration via P-element vectors. Sequences between -209 and -24 were necessary for normally regulated expression, although genes lacking these sequences could be expressed at 10 to 50% of wild-type levels at specific developmental times. These genes showed components of normal developmental expression, which suggests that they retain some regulatory elements. All Ddc genes lacking the normal immediate 5'-flanking sequences were grossly deficient in larval central nervous system expression. Thus, this upstream region must contain at least one element necessary for this expression. A mutated Ddc gene without a normal TATA boxlike sequence used the normal RNA start points, indicating that this sequences is not required for start point specificity.

Alcohol Dehydrogenase↗
PubMed2000

Biosynthesis and regulation of expression of proteoglycans.

Proteoglycans are a family of complex macromolecules characterized by the presence of one or more glycosaminoglycan chains covalently linked to a polypeptide backbone. Although originally named and categorized on the basis of the glycosaminoglycan substituent, increasingly they are being identified as members of gene families that encode their different core proteins. Proteoglycans are found predominantly in the extracellular matrix (ECM) or associated with the cell surface of most eucaryotic cells where they bind to other matrix- and cell-associated components. Their ability to be so interactive stems in large part from their structural diversity, which arises from variations in polysaccharide type, size and composition as well as core protein primary sequence, domain arrangement, degree of substitution and distribution of polysaccharide chains. Considering the complexity of proteoglycan molecules, often having modular core protein domains and posttranslational modifications that vary with developmental setting, the various steps of synthesis and processing are most likely highly regulated. Furthermore, regulation of proteoglycan expression is even more complex as they frequently are expressed transiently by multiple cell types and in different developmental time frames. Elucidation of cell- and developmental-specific control elements which regulate the expression of these complex macromolecular families are only beginning.

Animals↗
PubMed1988

Molecular evidence for early activity-dependent development of hamster motor neurons.

Monoclonal antibody Cat-301 recognizes a surface antigen on subsets of neurons in many areas of the mammalian CNS, including Y-cells in the cat dorsal lateral geniculate nucleus (LGN) and spinal motor neurons in several species. We have shown previously that the Cat-301 antigen is expressed relatively late in postnatal development, with a time course that matches that of late developmental features of both LGN and spinal cord neurons. The developmental time course of the expression of the Cat-301 antigen in the LGN correlates with the period during which visual deprivation can alter LGN Y-cells. Neonatal visual deprivation (by monocular lid suture or dark rearing) suppresses Cat-301 expression on Y-cells, while deprivation in adult animals has no effect on antigen expression. These results suggested that the onset of Cat-301 immunoreactivity provides a positive molecular marker for the end of a critical period in cat visual system development. To determine if Cat-301 might be a general marker for experience-dependent development in other areas of the CNS we have examined antigen expression on hamster spinal cord motor neurons. Here, we report that Cat-301 immunoreactivity develops on hamster motor neurons between postnatal days 7 and 14. Altering neuromuscular activity by sciatic nerve crush or thoracic hemicordotomy inhibits Cat-301 expression on motor neurons if performed before the onset of Cat-301 immunoreactivity. Other motor neuron antigens are unaffected by this procedure. In adult animals, nerve crush or cordotomy has no effect on Cat-301 immunoreactivity, demonstrating that Cat-301 expression is not simply dependent on ongoing neural activity. These observations suggest that motor neurons, like LGN neurons, require some pattern of neuronal activity during a critical period in development and, further, that the phenotypic changes in neurons consequent to early activity are reflected by the expression of specific molecules. The identification and characterization of such molecules may yield a description of the molecular mechanisms of experience-dependent development.

Aging↗
PubMedDate not supplied

Analyzing evolutionary patterns in amniote embryonic development.

Heterochrony (differences in developmental timing between species) is a major mechanism of evolutionary change. However, the dynamic nature of development and the lack of a universal time frame makes heterochrony difficult to analyze. This has important repercussions in any developmental study that compares patterns of morphogenesis and gene expression across species. We describe a method that makes it possible to quantify timing shifts in embryonic development and to map their evolutionary history. By removing a direct dependence on traditional staging series, through the use of a relative time frame, it allows the analysis of developmental sequences across species boundaries. Applying our method to published data on vertebrate development, we identified clear patterns of heterochrony. For example, an early onset of various heart characters occurs throughout amniote evolution. This suggests that advanced (precocious) heart development arose in evolutionary history before endothermy. Our approach can be adapted to analyze other forms of comparative dynamic data, including patterns of developmental gene expression.

Age Factors↗
PubMed2003

Temporal regulation of microRNA expression in Drosophila melanogaster mediated by hormonal signals and broad-Complex gene activity.

lin-4 and let-7 are founding members of an extensive family of genes that produce small transcripts, termed microRNAs (miRNAs). In Caenorhabditis elegans, lin-4 and let-7 control the timing of postembryonic events by translational repression of target genes, permitting progression from early to late developmental programs. To identify Drosophila melanogaster miRNAs that could play similar roles in the control of developmental timing, we characterized the developmental expression profile of 24 miRNAs in Drosophila, and found 7 miRNAs that are either upregulated or downregulated in conjunction with metamorphosis. The upregulation of three of these miRNAs (mir-100, mir-125, and let-7), and the downregulation of a fourth (mir-34) requires the hormone ecdysone (Ecd) and the activity of the Ecd-inducible gene Broad-Complex. Interestingly, mir-125 is a putative homologue of lin-4. mir-100, -125, and let-7 are clustered within an 800-bp region on chromosome 2L, suggesting that these three miRNAs may be coordinately regulated via common cis-acting elements during metamorphosis. In S2 cells, Ecd and the juvenile hormone analog methoprene exert opposite effects on the expression of these four miRNAs, indicating the participation of both these hormones in the temporal regulation of mir-34, -100, -125, and let-7 expression in vivo.

Animals↗
PubMed1995

Perinatal development of action potential propagation in cat rubrospinal axons.

1. The development of action potential conduction was studied by intracellular recording of antidromic spikes in cat rubrospinal cells. 2. The distance between the C1 and L1 spinal segments increased linearly from 5.6 cm at embryonic day (E) 59 to 9.8 cm at postnatal day (P) 30. 3. The conduction time from the C1 segment to the rubrospinal neuron soma, estimated from antidromic spike latency evoked by stimulation of the C1 segment, decreased rapidly prior to birth and then slowly thereafter. This coincided with a reduction in conduction time variation between cells. 4. The conduction time from the red nucleus to the L1 segment followed a similar time course during development. The conduction time reached the adult value by P30, at which time the spinal cord is only half the adult length. 5. The conduction velocity between the C1 and L1 segments increased monotonically between E59 and P30, from a low of 1 m s-1 to a maximum of 34 m s-1. 6. The rise time of rubrospinal neuron somadendritic spikes followed a developmental time course similar to that for conduction time. 7. Myelination of rubrospinal axons, as judged by the presence of myelinated segment spikes, began to occur prior to E59. 8. These findings suggest that development of action potential propagation in rubrospinal cells can be divided into an early and a late stage: conduction time reaches the adult value during the early stage, i.e. by the first postnatal month, and is maintained during the late stage. We propose that myelination, axon diameter increase and maturation of membrane properties act to reduce conduction time to adult values during the early stage, while a proportional increase in fibre diameter with axonal length results in a constant conduction time during the late stage.

Action Potentials↗
PubMed1998

Ethanol-induced neural crest apoptosis is coincident with their endogenous death, but is mechanistically distinct.

The ability of both acute and chronic ethanol exposures to elicit cell death within specific embryonic and adult tissues is believed to partly underlie ethanol's pathogenicity; however, the mechanism underlying this cell death is unknown. This study partially characterized the mechanism of ethanol-induced neural crest cell death in a chick embryo model of fetal alcohol syndrome. In situ DNA end-labeling demonstrated this cell death was apoptotic and occurred at embryonic ethanol levels as low as 42 mM. Regardless of the initial exposure time, this apoptosis always appeared at a distinct developmental time point simultaneous with the normal deletion of a cranial neural crest subset. This suggested that ethanol might act through aberrant activation of the endogenous death pathway; however, ethanol exposure failed to induce two components of this pathway, the homeotic transcription factor msx-2 and the growth factor bone morphogenetic protein 4. Both endogenous and ethanol-induced death were blocked by local application of an interleukin-1beta converting enzyme/CED-3 protease (caspase) inhibitor, showing that the two paths converge mechanistically and suggesting the potential to prevent this aspect of ethanol's teratogenicity. Ethanol exposure did not significantly alter cell proliferation within neural crest-populated regions, suggesting that susceptibility to ethanol-induced death did not involve exit from the cell cycle. Apoptotic deletion of cranial neural crest could partially explain the craniofacial deficits characteristic of the fetal alcohol syndrome.

Adult↗
PubMed1984

Early programming of maturation competence in mouse oogenesis.

Growing mouse oocytes incompetent to mature were freed of attached granulosa cells at different stages of growth, and cultured in vitro in the presence of fibroblast monolayers and/or their products. In these culture conditions, although growth was arrested, isolated oocytes survived in vitro for several days, and finally resumed meiosis spontaneously, progressing up to metaphase I. The culture time length needed for in vitro acquisition of the capacity to mature was inversely related to the initial oocyte size at the time of isolation from granulosa cells, and closely corresponded to developmental timing of acquisition of such ability in vivo. We conclude that the acquisition of mouse oocyte competence to mature follows a definite time program, which is independent of the presence of granulosa cells and of heterologous cell contacts, at least within the developmental stages studied.

Animals↗
PubMed1973

The acquisition of specificity in cutaneous sensory neurons: a reconsideration of the integumental specification hypothesis.

Neuronal specificity in cutaneous sensory nerve cells has been postulated to arise from "inductive interactions" between the cell's randomly outgrown peripheral neurite and local biochemical markers in the skin. Here was apply this integumental specification hypothesis to data recently obtained on the wiping-reflex behavior of frogs skin-grafted at various times during larval life. Deductions are generated about the developmental time course of the postulated nerve-skin interactions and two predictions are formulated and tested. Because the results of serial skin rotation experiments contradict the predictions, we conclude that the currently held hypothesis must be seriously questioned.

Animals↗
PubMed2003

Intra- and interspecific interactions between Lysiphlebus testaceipes and Lipolexis scutellaris (Hymenoptera: Aphidiidae) reared on Toxoptera citricida (Homoptera: Aphididae).

Classical biological control of the brown citrus aphid Toxoptera citricida Kirkaldy in Florida has involved the release of Lipolexis scutellaris Mackauer. Lysiphlebus testaceipes Cresson is already present in Florida and also parasitizes T. citricida. Because parasitoid-parasitoid interactions may affect the establishment of a newly introduced parasitoid species, intra- and interspecific larval interactions of both parasitoids were studied in the laboratory using T. citricida reared on citrus. Five time intervals were allowed between successive oviposition opportunities. Early developmental times were determined for both parasitoids: eggs of L. testaceipes and L. scutellaris hatched after 54.3 and 61.7 h, while molt to second instar occurred after 73.3 and 87.1 h, respectively, after oviposition at 22 degrees C. At intervals <12 h, both parasitoids had a greater tendency to multiparasitize than to superparasitize, and the tendency to superparasitize or multiparasitize decreased with an increase in time between successive oviposition opportunities. Of the 10 interspecific interactions studied, 5 produced a winning wasp species, 3 of which could be explained by the hypothesis of physical conflict. A combination of development time, age of competing larvae, and oviposition sequence were responsible for the outcomes observed. Neither parasitoid proved to be intrinsically superior when interspecific competition occurs in second- and third-instar T. citricida, indicating there is no reason to suggest that they cannot coexist in Florida citrus groves.

Animals↗
PubMed1983

Development of sensory-motor synapses in the spinal cord of the frog.

The development and specificity of monosynaptic sensory-motor synapses were studied in the brachial spinal cord of bullfrog tadpoles. Intracellular and extracellular recordings were made from motoneurones innervating several different muscles of the forelimb. Excitatory synaptic potentials (e.p.s.p.s) were elicited by stimulation of various peripheral muscle nerves. Sensory and motor axons in the triceps brachii muscle nerves were electrically excitable at stage XIII, the earliest stage studied. Their conduction velocities were 0.2-0.4 m/s. These velocities increased during subsequent development so that by stage XXII they were approximately 5 m/s. Before stage XVII, synaptic potentials evoked in motoneurones by stimulation of the triceps sensory fibres had a long central latency and fatigued easily. These potentials were probably mediated polysynaptically. At stage XVII, the first short-latency triceps synaptic potentials appeared. They had central latencies of less than 3 ms and represented the direct, monosynaptic input from muscle sensory cells on to motoneurones. During subsequent development the percentage of triceps motoneurones innervated by triceps sensory fibres increased, while the number of long-latency polysynaptic inputs decreased. Both the electrical and chemical components, characteristic of these monosynaptic e.p.s.p.s in adult frogs, were prominent from the time the e.p.s.p.s first appeared. The pattern of innervation of brachial motoneurones by triceps sensory afferents was specific from the beginning. Triceps sensory fibres innervated most triceps motoneurones but very few subscapular or pectoralis motoneurones, just as in adult frogs. At no time were there appreciable numbers of 'aberrant' connexions. The developmental time course of several different classes of sensory-motor connexions was similar. Thus the synaptic specificity of this system cannot be explained by a differential timing of synaptogenesis.

Animals↗
PubMed2003

Time and the après-coup.

The author explores the different temporalities of developmental time, après-coup and what she calls 'reverberation time'. She considers the paradoxical temporality of the 'here and now', showing that it is not pure present, and describes at the micro-level of sessional material how progressive and retrospective time go inherently together, one being a requisite for the other.

Freudian Theory↗
PubMed1995

Dominant negative mutants of the Cdc2 kinase uncouple cell division from iterative plant development.

Because plant cells do not move and are surrounded by a rigid cell wall, cell division rates and patterns are believed to be directly responsible for generating new structures throughout development. To study the relationship between cell division and morphogenesis, transgenic tobacco and Arabidopsis plants were constructed expressing dominant mutations in a key regulator of the Arabidopsis cell cycle, the Cdc2a kinase. Plants constitutively overproducing the wild-type Cdc2a or the mutant form predicted to accelerate the cell cycle did not exhibit a significantly altered development. In contrast, a mutation expected to arrest the cell cycle abolished cell division when expressed in Arabidopsis, whereas some tobacco plants constitutively producing this mutant protein were recovered. These plants had a reduced histone H1 kinase activity and contained considerably fewer cells. These cells were, however, much larger and underwent normal differentiation. Morphogenesis, histogenesis and developmental timing were unaffected. The results indicate that, in plants, the developmental controls defining shape can act independently from cell division rates.

Amino Acid Sequence↗
PubMed2001

Protein kinase C isoform expression and activity in the mouse heart.

The expression of protein kinase C (PKC) isoforms in the developing murine ventricle was studied using Western blotting, assays of PKC activity, and immunoprecipitations. The abundance of two Ca2+-dependent isoforms, PKCalpha and PKCbetaII, as well as two Ca2+-independent isoforms, PKCdelta and PKCepsilon, decreased during postnatal development to <15% of the levels detected at embryonic day 18. The analysis of the subcellular distribution of the four isoforms showed that PKCdelta and PKCepsilon were associated preferentially with the particulate fraction in fetal ventricles, indicating a high intrinsic activation state of these isoforms at this developmental time point. The expression of PKCalpha in cardiomyocytes underwent a developmental change. Although preferentially expressed in neonatal cardiomyocytes, this isoform was downregulated in adult cardiomyocytes. In fast-performance liquid chromatography-purified ventricular extracts, the majority of PKC activity was Ca2+-independent in both fetal and adult ventricles. Immunoprecipitation assays indicated that PKCdelta and PKCepsilon were responsible for the majority of the Ca2+-independent activity. These studies indicate a prominent role for Ca2+-independent PKC isoforms in the mouse heart.

Age Factors↗
PubMed2006

Development of Pseudacteon nocens (Diptera: Phoridae) on Solenopsis invicta and Solenopsis richteri fire ants (Hymenoptera: Formicidae).

We studied the developmental performance of the large morph of Pseudacteon nocens Borgmeier (Diptera: Phoridae), a prospective biological control agent of imported fire ants (Hymenoptera: Formicidae). We measured selected life history traits of this parasitoid as a function of 1) host species (Solenopsis invicta Buren versus Solenopsis richteri Forel), 2) temperature (22 versus 28 degrees C), 3) source population of the fly (Corrientes and Santiago del Estero, Argentina), and 4) varied size distributions of offered host ants. Developmental periods were influenced by host species, although the populations responded in opposing manners. Developmental times, however, were most strongly influenced by temperature with total developmental periods lengthened by 17-32% at 22 degrees C. Pupal mortality was also significantly lower at this temperature. Although numbers of progeny per female were significantly higher for the Corrientes population, we found no significant differences in progeny per female according to host species. Interestingly, we found that females were larger than males, and flies from Corrientes were larger than those from Santiago del Estero, even after statistical adjustments for host size. The modal frequency of host size elected in all treatment combinations tested was identical (0.6 mm), a size that represented the apparent threshold for producing female progeny. These laboratory and additional field observations demonstrate considerable interpopulational variation in P. nocens and lend further support to the applied approach focusing at the population, as opposed to the species level, with respect to both source and target areas for classical biological control introductions of Pseudacteon flies.

Animals↗
PubMed1984

Development profile of the heat shock response in early embryos of Drosophila.

Drosophila melanogaster embryos reared at 22 degrees C were subjected to a mild heat shock (40 min at 37 degrees C) at various ages in order to determine whether there are changes in the heat shock response during embryogenesis. The effects of the heat shock were measured by assaying (1), subsequent developmental abnormalities (2), developmental time (3), hatchability, and (4), the ability to synthesize the heat shock proteins as assayed by 35S-methionine pulse labeling followed by protein separations using both one-and two-dimensional polyacrylamide gel electrophoresis. Our data show that, first, proteins with molecular weights similar to those of six of the seven major heat shock proteins are normally found in the embryo at control temperatures (22 degrees C); second, that the pregastrula embryo (stages 2-6) is not capable of displaying any aspect of the heat shock response upon treatment, although it may possess all of the so-called heat shock proteins; third, that the complete heat shock response is acquired very rapidly by early gastrula embryos; and fourth, that the heat shock treatment brings about developmental delays and/or abnormalities, depending on the developmental stage of the embryo at the time of the treatment. These developmental abnormalities appear to stem from the failure of early embryos to completely inhibit their synthesis of non-heat-shock proteins. In the light of these findings, it becomes important not to base conclusions about the putative presence of a heat shock response in a particular tissue or developmental stage solely on the presence or absence of the heat shock proteins.

Animals↗