Isolation of temperature sensitive mutations blocking clone development inDrosophila melanogaster, and the effects of a temperature sensitive cell lethal mutation on pattern formation in imaginal discs

Genotoxic action of bifenthrin nanoparticles and its effect on the development, productivity, and behavior of Drosophila melanogaster

Rapid development of nanotechnology, particularly nanoparticles of pesticides, has facilitated the transformation of traditional agriculture. However, testing their effectiveness is essential for avoiding any environmental or adverse human health risk attributed to nanoparticle-based formulations, especially insecticides. Recently, organic nanoparticles of bifenthrin, a pyrethroid insecticide, were successfully synthesized by laser ablation of solids in liquid technique, with the most probable size of 5 nm. The aim of the present study was to examine the effects of acute exposure to bifenthrin (BIF) or bifenthrin nanoparticles (BIFNP) on larval-adult viability, developmental time, olfactory capacity, longevity, productivity defined as the number of eggs per couple, and genotoxicity in Drosophila melanogaster. Data demonstrated that BIFNP produced a marked delay in developmental time, significant reduction in viability and olfactory ability compared to BIF. No marked differences were detected between BIF and BIFNP on longevity and productivity. Genotoxicity findings indicated that only BIF, at longer exposure duration increased genetic damage.

Intrinsic and damage-induced JAK/STAT signaling regulate developmental timing by the Drosophila prothoracic gland

Development involves tightly paced, reproducible sequences of events, yet it must adjust to conditions external to it, such as resource availability and organismal damage. A major mediator of damage-induced immune responses in vertebrates and insects is JAK/STAT signaling. At the same time, JAK/STAT activation by the Drosophila Upd cytokines is pleiotropically involved in normal development of multiple organs. Whether inflammatory and developmental JAK/STAT roles intersect is unknown. Here, we show that JAK/STAT is active during development of the prothoracic gland (PG), which controls metamorphosis onset through ecdysone production. Reducing JAK/STAT signaling decreased PG size and advanced metamorphosis. Conversely, JAK/STAT hyperactivation by overexpression of pathway components or SUMOylation loss caused PG hypertrophy and metamorphosis delay. Tissue damage and tumors, known to secrete Upd cytokines, also activated JAK/STAT in the PG and delayed metamorphosis, at least in part by inducing expression of the JAK/STAT target Apontic. JAK/STAT damage signaling, therefore, regulates metamorphosis onset by co-opting its developmental role in the PG. Our findings in Drosophila provide insights on how systemic effects of damage and cancer can interfere with hormonally controlled development and developmental transitions.

Summary: Damage signaling from tumors mediated by JAK/STAT-activating Upd cytokines delays the Drosophila larva–pupa transition through co-option of a JAK/STAT developmental role in the prothoracic gland.

The steroid-hormone ecdysone coordinates parallel pupariation neuromotor and morphogenetic subprograms via epidermis-to-neuron Dilp8-Lgr3 signal induction

Innate behaviors consist of a succession of genetically-hardwired motor and physiological subprograms that can be coupled to drastic morphogenetic changes. How these integrative responses are orchestrated is not completely understood. Here, we provide insight into these mechanisms by studying pupariation, a multi-step innate behavior of Drosophila larvae that is critical for survival during metamorphosis. We find that the steroid-hormone ecdysone triggers parallel pupariation neuromotor and morphogenetic subprograms, which include the induction of the relaxin-peptide hormone, Dilp8, in the epidermis. Dilp8 acts on six Lgr3-positive thoracic interneurons to couple both subprograms in time and to instruct neuromotor subprogram switching during behavior. Our work reveals that interorgan feedback gates progression between subunits of an innate behavior and points to an ancestral neuromodulatory function of relaxin signaling.

Regulation of Body Size and Growth Control

The control of body and organ growth is essential for the development of adults with proper size and proportions, which is important for survival and reproduction. In animals, adult body size is determined by the rate and duration of juvenile growth, which are influenced by the environment. In nutrient-scarce environments in which more time is needed for growth, the juvenile growth period can be extended by delaying maturation, whereas juvenile development is rapidly completed in nutrient-rich conditions. This flexibility requires the integration of environmental cues with developmental signals that govern internal checkpoints to ensure that maturation does not begin until sufficient tissue growth has occurred to reach a proper adult size. The Target of Rapamycin (TOR) pathway is the primary cell-autonomous nutrient sensor, while circulating hormones such as steroids and insulin-like growth factors are the main systemic regulators of growth and maturation in animals. We discuss recent findings in Drosophila melanogaster showing that cell-autonomous environment and growth-sensing mechanisms, involving TOR and other growth-regulatory pathways, that converge on insulin and steroid relay centers are responsible for adjusting systemic growth, and development, in response to external and internal conditions. In addition to this, proper organ growth is also monitored and coordinated with whole-body growth and the timing of maturation through modulation of steroid signaling. This coordination involves interorgan communication mediated by Drosophila insulin-like peptide 8 in response to tissue growth status. Together, these multiple nutritional and developmental cues feed into neuroendocrine hubs controlling insulin and steroid signaling, serving as checkpoints at which developmental progression toward maturation can be delayed. This review focuses on these mechanisms by which external and internal conditions can modulate developmental growth and ensure proper adult body size, and highlights the conserved architecture of this system, which has made Drosophila a prime model for understanding the coordination of growth and maturation in animals.

Network-regulated organ allometry: The developmental regulation of morphological scaling

Morphological scaling relationships, or allometries, describe how traits grow coordinately and covary among individuals in a population. The developmental regulation of scaling is essential to generate correctly proportioned adults across a range of body sizes, while the mis-regulation of scaling may result in congenital birth defects. Research over several decades has identified the developmental mechanisms that regulate the size of individual traits. Nevertheless, we still have poor understanding of how these mechanisms work together to generate correlated size variation among traits in response to environmental and genetic variation. Conceptually, morphological scaling can be generated by size-regulatory factors that act directly on multiple growing traits (trait-autonomous scaling), or indirectly via hormones produced by central endocrine organs (systemically regulated scaling), and there are a number of well-established examples of such mechanisms. There is much less evidence, however, that genetic and environmental variation actually acts on these mechanisms to generate morphological scaling in natural populations. More recent studies indicate that growing organs can themselves regulate the growth of other organs in the body. This suggests that covariation in trait size can be generated by network-regulated scaling mechanisms that respond to changes in the growth of individual traits. Testing this hypothesis, and one of the main challenges of understanding morphological scaling, requires connecting mechanisms elucidated in the laboratory with patterns of scaling observed in the natural world. This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Comparative Development and Evolution > Organ System Comparisons Between Species.

Body Size and Tissue-Scaling Is Regulated by Motoneuron-Derived Activinß in Drosophila melanogaster

Correct scaling of body and organ size is crucial for proper development, and the survival of all organisms. Perturbations in circulating hormones, including insulins and steroids, are largely responsible for changing body size in response to both genetic and environmental factors. Such perturbations typically produce adults whose organs and appendages scale proportionately with final size. The identity of additional factors that might contribute to scaling of organs and appendages with body size is unknown. Here, we report that loss-of-function mutations in DrosophilaActivinβ (Actβ), a member of the TGF-β superfamily, lead to the production of small larvae/pupae and undersized rare adult escapers. Morphometric measurements of escaper adult appendage size (wings and legs), as well as heads, thoraxes, and abdomens, reveal a disproportional reduction in abdominal size compared to other tissues. Similar size measurements of selected Actβ mutant larval tissues demonstrate that somatic muscle size is disproportionately smaller when compared to the fat body, salivary glands, prothoracic glands, imaginal discs, and brain. We also show that Actβ control of body size is dependent on canonical signaling through the transcription-factor dSmad2 and that it modulates the growth rate, but not feeding behavior, during the third-instar period. Tissue- and cell-specific knockdown, and overexpression studies, reveal that motoneuron-derived Actβ is essential for regulating proper body size and tissue scaling. These studies suggest that, unlike in vertebrates, where Myostatin and certain other Activin-like factors act as systemic negative regulators of muscle mass, in Drosophila, Actβ is a positive regulator of muscle mass that is directly delivered to muscles by motoneurons. We discuss the importance of these findings in coordinating proportional scaling of insect muscle mass to appendage size.

Developmental cost of leg-regenerated Coccinella septempunctata (Coleoptera: Coccinellidae)

As larval cannibalism is common under intensive rearing conditions, leg regeneration can help ladybugs adapt to the competitive environment, but whether the leg regeneration leads to side effects on development remains unclear. To analyze the potentially developmental cost of leg regeneration, the developmental period and weight of leg-regenerated Coccinella septempunctata were studied in the laboratory. The results showed that, when the time intervals between the emergency of 4th-instar larva and leg amputation increased, the developmental period of leg-regenerated 4th-instar larvae was gradually prolonged. Significantly developmental delay were also examined at prepupal and pupal stages, and various timings of leg amputation affected the periods of leg-regenerated prepupae/pupae similarly. After the leg was amputated at different larval instars, the developmental delay only occurred at the larval instar when the leg was amputated, whereas other larval instars failed to be extended, and the developmental periods of leg-regenerated prepupae/pupae were affected similarly by the instars of leg amputation. Developmental delays possibly resulted in more consumption by leg-regenerated larvae, and then weight gains at prepupal/pupal stages, but different larval instars of leg amputation affected the weight gain similarly. Both the developmental delay (at 4th-instar larval, prepupal and pupal stages) and weight gain (at pupal and adult stages) in complete/bilateral amputation were longer or greater than those in half/unilateral amputation. However, the thoracic locations of leg amputation impacted the developmental delay and weight gain similarly. Our study indicates that although leg regeneration triggers the developmental cost decreasing the competitive superiority or agility, C. septempunctata larvae still choose to completely regenerate the leg to adapt to complex environments. Thus, in order to remain competitive at adult stages, leg-impaired larvae may make an investment tradeoff between leg regeneration and developmental cost.

The (ongoing) problem of relative growth

Differential growth, the phenomenon where parts of the body grow at different rates, is necessary to generate the complex morphologies of most multicellular organisms. Despite this central importance, how differential growth is regulated remains largely unknown. Recent discoveries, particularly in insects, have started to uncover the molecular-genetic and physiological mechanisms that coordinate growth among different tissues throughout the body and regulate relative growth. These discoveries suggest that growth is coordinated by a network of signals that emanate from growing tissues and central endocrine organs. Here we review these findings and discuss their implications for understanding the regulation of relative growth and the evolution of morphology.

The Systemic Control of Growth

Growth is a complex process that is intimately linked to the developmental program to form adults with proper size and proportions. Genetics is an important determinant of growth, as exemplified by the role of local diffusible molecules setting up organ proportions. In addition, organisms use adaptive responses allowing modulating the size of individuals according to environmental cues, for example, nutrition. Here, we describe some of the physiological principles participating in the determination of final individual size.

Injury response checkpoint and developmental timing in insects

In insects, localized tissue injury often leads to global (organism-wide) delays in development and retarded metamorphosis. In Drosophila, for example, injuries to the larval imaginal discs can retard pupariation and prolong metamorphosis. Injuries induced by treatments such as radiation, mechanical damage and induction of localized cell death can trigger similar delays. In most cases, the duration of the developmental delay appears to be correlated with the extent of damage, but the effect is also sensitive to the developmental stage of the treated animal. The proximate cause of the delays is likely a disruption of the ecdysone signaling pathway, but the intermediate steps leading from tissue injury and/or regeneration to that disruption remain unknown. Here, we review the evidence for injury-induced developmental delays, and for a checkpoint or checkpoints associated with the temporal progression of development and the on-going efforts to define the mechanisms involved.

Developmental checkpoints and feedback circuits time insect maturation

The transition from juvenile to adult is a fundamental process that allows animals to allocate resource toward reproduction after completing a certain amount of growth. In insects, growth to a species-specific target size induces pulses of the steroid hormone ecdysone that triggers metamorphosis and reproductive maturation. The past few years have seen significant progress in understanding the interplay of mechanisms that coordinate timing of ecdysone production and release. These studies show that the neuroendocrine system monitors complex size-related and nutritional signals, as well as external cues, to time production and release of ecdysone. Based on results discussed here, we suggest that developmental progression to adulthood is controlled by checkpoints that regulate the genetic timing program enabling it to adapt to different environmental conditions. These checkpoints utilize a number of signaling pathways to modulate ecdysone production in the prothoracic gland. Release of ecdysone activates an autonomous cascade of both feedforward and feedback signals that determine the duration of the ecdysone pulse at each developmental transitions. Conservation of the genetic mechanisms that coordinate the juvenile-adult transition suggests that insights from the fruit fly Drosophila will provide a framework for future investigation of developmental timing in metazoans.

Tissue damage disrupts developmental progression and ecdysteroid biosynthesis in Drosophila

In humans, chronic inflammation, severe injury, infection and disease can result in changes in steroid hormone titers and delayed onset of puberty; however the pathway by which this occurs remains largely unknown. Similarly, in insects injury to specific tissues can result in a global developmental delay (e.g. prolonged larval/pupal stages) often associated with decreased levels of ecdysone – a steroid hormone that regulates developmental transitions in insects. We use Drosophila melanogaster as a model to examine the pathway by which tissue injury disrupts developmental progression. Imaginal disc damage inflicted early in larval development triggers developmental delays while the effects are minimized in older larvae. We find that the switch in injury response (e.g. delay/no delay) is coincident with the mid-3rd instar transition – a developmental time-point that is characterized by widespread changes in gene expression and marks the initial steps of metamorphosis. Finally, we show that developmental delays induced by tissue damage are associated with decreased expression of genes involved in ecdysteroid synthesis and signaling.

The regulation of organ size in Drosophila: physiology, plasticity, patterning and physical force

The correct regulation of organ size is a fundamental developmental process, the failure of which can compromise organ function and organismal integrity. Consequently, the mechanisms that regulate organ size have been subject to intense research. This research has highlighted four classes of mechanism that are involved in organ size regulation: physiology, plasticity, patterning and physical force. Nevertheless, how these mechanisms are integrated and converge on the cellular process that regulate organ growth is unknown. One group of animals where this integration is beginning to be achieved is in the insects. Here, I review the different mechanisms that regulate organ size in insects, and describe our current understanding of how these mechanisms interact. The genes and hormones involved are remarkably conserved in all animals, so these studies in insects provide a precedent for future research on organ size regulation in mammals.

The coordination of growth among Drosophila organs in response to localized growth-perturbation

The developmental mechanisms by which growth is coordinated among developing organs are largely unknown and yet are essential to generate a correctly proportioned adult. In particular, such coordinating mechanisms must be able to accommodate perturbations in the growth of individual organs caused by environmental or developmental stress. By autonomously slowing the growth of the developing wing discs within Drosophila larvae, we show that growing organs are able to signal localized growth perturbation to the other organs in the body and slow their growth also. Growth rate is so tightly coordinated among organs that they all show approximately the same reduction in growth rate as the developing wings, thereby maintaining their correct size relationship relative to one another throughout development. Further, we show that the systemic growth effects of localized growth-perturbation are mediated by ecdysone. Application of ecdysone to larvae with growth-perturbed wing discs rescues the growth rate of other organs in the body, indicating that ecdysone is limiting for their growth, and disrupts the coordination of their growth with growth of the wing discs. Collectively our data demonstrate the existence of a novel growth-coordinating mechanism in Drosophila that synchronizes growth among organs in response to localized growth perturbation.

Cell autonomy of two DNA-repair mutations inDrosophila melanogaster

By means of genetic mosaics we have studied the cell autonomy ofmei-41andmei-9, two loci involved in DNA metabolism. The frequency of spontaneous somatic spots resulting from unrepaired chromosome damage and the sensitivity of mutant cells to killing by X-irradiation - two traits indicative of deficient DNA repair - have been analysed at the cellular level. The results show that: (1) The effect of both mutations on chromosome stability is cell autonomous. (2) After 1000 r of X-irradiation practically all the cells homozygous formei-41disappear while about one-third of the cells homozygous formei-9asurvive the irradiation. The possibility of using these mutants as tools to approach developmental problems is discussed.

Imaginal discs regulate developmental timing in Drosophila melanogaster

The regulation of body size in animals involves mechanisms that terminate growth. In holometabolous insects growth ends at the onset of metamorphosis and is contingent on their reaching a critical size in the final larval instar. Despite the importance of critical size in regulating final body size, the developmental mechanisms regulating critical size are poorly understood. Here we demonstrate that the developing adult organs, called imaginal discs, are a regulator of critical size in larval Drosophila. We show that damage to, or slow growth of, the imaginal discs is sufficient to retard metamorphosis both by increasing critical size and extending the period between attainment of critical size and metamorphosis. Nevertheless, larvae with damaged and slow growing discs metamorphose at the same size as wild-type larvae. In contrast, complete removal of all imaginal tissue has no effect on critical size. These data indicate that both attainment of critical size and the timely onset of metamorphosis are regulated by the imaginal discs in Drosophila, and suggest that the termination of growth is coordinated among growing tissues to ensure that all organs attain a characteristic final size.

Size and shape: the developmental regulation of static allometry in insects

Among all organisms, the size of each body part or organ scales with overall body size, a phenomenon called allometry. The study of shape and form has attracted enormous interest from biologists, but the genetic, developmental and physiological mechanisms that control allometry and the proportional growth of parts have remained elusive. Recent progress in our understanding of body-size regulation provides a new synthetic framework for thinking about the mechanisms and the evolution of allometric scaling. In particular, insulin/IGF signaling, which plays major roles in longevity, diabetes and the regulation of cell, organ and body size, might also be centrally involved in regulating organismal shape. Here we review recent advances in the fields of growth regulation and endocrinology and use them to construct a developmental model of static allometry expression in insects. This model serves as the foundation for a research program that will result in a deeper understanding of the relationship between growth and form, a question that has fascinated biologists for centuries.

The control of body size in insects

Control mechanisms that regulate body size and tissue size have been sought at both the cellular and organismal level. Cell-level studies have revealed much about the control of cell growth and cell division, and how these processes are regulated by nutrition. Insulin signaling is the key mediator between nutrition and the growth of internal organs, such as imaginal disks, and is required for the normal proportional growth of the body and its various parts. The insulin-related peptides of insects do not appear to control growth by themselves, but act in conjunction with other hormones and signaling molecules, such as ecdysone and IDGFs. Size regulation cannot be understood solely on the basis of the mechanisms that control cell size and cell number. Size regulation requires mechanisms that gather information on a scale appropriate to the tissue or organ being regulated. A new model mechanism, using autocrine signaling, is outlined by which tissue and organ size regulation can be achieved. Body size regulation likewise requires a mechanism that integrates information at an appropriate scale. In insects, this mechanism operates by controlling the secretion of ecdysone, which is the signal that terminates the growth phase of development. The mechanisms for size assessment and the pathways by which they trigger ecdysone secretion are diverse and can be complex. The ways in which these higher-level regulatory mechanisms interact with cell- and molecular- level mechanisms are beginning to be elucidated.

The Drosophila homeotic gene moira regulates expression of engrailed and HOM genes in imaginal tissues

moira is a member of the trithorax group of homeotic gene regulators in Drosophila melanogaster. We show that moira is required for the function of multiple homeotic genes of the Antennapedia and bithorax complexes (HOM genes) in most imaginal tissues and that the requirement for moira function is at the level of transcription. moira is also required for transcription of the engrailed segmentation gene in the imaginal wing disc. The abnormalities caused by the loss of moira function in germ cells suggests that at least one other target gene requires moira for normal oogenesis.

Developmental consequences of awdb3, a cell-autonomous lethal mutation of Drosophila induced by hybrid dysgenesis

In order to recover mutations affecting imaginal discs in a way which would allow the relevant genes to be readily cloned, a hybrid dysgenic screen was performed for mutations causing late larval/early pupal lethality. This paper describes that mutagenesis procedure and the phenotypes caused by the mutations that were recovered. Of 81 late larval/pupal lethal mutations that were recovered, 20 cause imaginal disc defects. These 20 mutations define 12 different genes. This paper also includes a description of the developmental defects caused by a mutation in one of those 12 genes which we have named abnormal wing discs (awd); the following paper (C. Dearolf, N. Tripoulas, J. Biggs, and A. Shearn, 1988, Dev. Biol. 129, 169-178) describes the cloning of the awd gene and an analysis of its pattern of transcription. awdb3 homozygotes develop at a normal rate until the end of the second larval instar, when their rate of development is reduced. After an extended third larval instar, they form puparia and die. Mutant wing discs have an abnormal morphology and extensive cell death. These abnormal wing discs, and also the leg and eye-antenna discs which appear to be morphologically normal, differentiate poorly or not at all when injected into metamorphosing larvae. Analysis of genetic mosaics indicates that the awdb3 mutation is expressed in a cell-autonomous manner in wing, leg, and eye-antenna discs. The larval brain and proventriculus in awdb3 homozygous third-instar larvae appear to be vacuolated due to the accumulation of lipid droplets. Mutant ovaries are unable to develop when injected into wild-type larvae, although mutant germ cells are capable of producing normal eggs.

The segment polarity gene costal-2 in Drosophila. II. The origin of imaginal pattern duplications

Imaginal pattern duplications caused by hypomorphic expression of the segment polarity gene costal-2 are described. These affect the anteroposterior coordinate of the imaginal disc. A very small part of the pattern is deleted and a large number of additional pattern elements arise in a progressive order, anterior-most first followed by more and more posterior structures. Mosaic analyses show that the duplications arise nonautonomously in the larval stages but that the costal-2 gene is not required after early embryogenesis. Arguments that the duplications are the result of cell interactions and intercalary growth that themselves arise from an abnormal polarity of the embryonic segment are presented.

Clonal analysis of two mutations in the large subunit of RNA polymerase II of Drosophila

Two mutations in the gene, RpII215, were analyzed to determine their effects on cell differentiation and proliferation. The mutations differ in that one, RpII215ts (ts), only displays a conditional recessive lethality, while the other, RpII215Ubl (Ubl), is a recessive lethal mutation that also displays a dominant mutant phenotype similar to that caused by the mutation Ultrabithorax (Ubx). Ubl causes a partial transformation of the haltere into a wing; however, this transformation is more complete in flies carrying both Ubl and Ubx. The present study shows that patches of Ubl/-tissue in gynandromorphs are morphologically normal. cuticle that has lost the wild-type copy of the RpII215 locus fails to show a haltere to wing transformation, nor does it show the synergistic enhancement of Ubx by Ubl. We conclude that an interaction between the two RpII215 alleles, Ubl and RpII215+, is responsible for the mutant phenotype. Gynandromorphs carrying the ts allele, when raised at permissive temperature, display larger patches of ts/-cuticle than expected, possibly indicating that the proliferation of ts/+ cells is reduced. This might result from an antagonistic interaction between different RpII215 alleles. Classical negative complementation does not appear to be the cause of the antagonistic interactions described above, as only one RpII215 subunit is thought to be present in an active multimeric polymerase enzyme. We have therefore coined the term 'negative heterosis' to describe the aforementioned interactions. We also observed that the effects of mutationally altered RNA polymerase II on somatic cells are different from its effects on germ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of deficiencies in the engrailed region of Drosophila melanogaster

The engrailed gene of Drosophila melanogaster is believed to be involved in control of determination and differentiation of posterior compartments. en1/en1 causes a partial transformation of the posterior compartment of wing and first leg to mirror-image anterior, which prompted the hypothesis that engrailed + is a "selector gene" required for the posterior pathway decision. The incomplete transformation was thought due to residual en+ activity in en1; a deletion of engrailed (en28) was constructed to determine if a complete transformation can occur. en28 is homozygous lethal and cell lethal. en28/en1 survives to adult stage, but causes a weaker transformation than en1/en1, indicating that en1 is not a simple hypomorph. A more distal deletion, en30, survives over en-lethal alleles. Both en30/en1 and en28/en30 survive to adult stage, but do not cause a stronger posterior to anterior transformation than en1/en1; thus this effect may be allele specific. New abnormalities included (1) transformation of the posterior wing blade to haltere, an effect dependent on the bx+ (but not pbx+) pseudoallele of the bithorax complex; (2) abnormal bristle pattern, tarsal fusion, and degenerate posterior claws of all legs. Although these abnormalities are posterior compartment specific, they are not expected of a "selector gene." Thus the function of engrailed may be more complex than originally believed.

Distal into proximal (Dipr): a homoeotic mutation of Drosophila melanogaster

The morphology and genetical characteristics of a new dominant homoeotic mutation, called Distal into proximal (Dipr), are described. Dipr causes two main abnormalities, both of which are specific to distal regions of the adult appendages (i.e. the wing, haltere, legs, antenna, and proboscis); first that distal parts are reduced in size and second that the patterns found distally resemble those normally localised in more proximal parts. The mutation maps to the right arm of chromosome 3 and is associated with an inversion with breakpoints in 84D and 84F. Analysis of revertants of Dipr show that the right breakpoint of In(3R)Dipr is the one responsible for the mutant phenotype. Complementation analyses of Dipr revertants and dosage studies of Dipr with different doses of Dipr+ indicate that the mutant is a hypermorph affecting the normal expression of a gene localised in 84F. The developmental significance of the mutation is discussed.

Distal regeneration and symmetry

A revision of the "polar coordinate model" shows how pattern formation in diverse regenerating systems can be understood in terms of strictly local cell interactions.

Chemical impurity produces extra compound eyes and heads in crickets

A chemical impurity isolated from commercially purchased acridine causes cricket embryos to develop extra compound eyes, branched antennae, extra antennae, and extra heads. Purified acridine does not produce similar duplications of cricket heads or head structures nor do the substituted acridines proflavine, acriflavine, or acridine orange. A dose-response relation exists such that the number and severity of abnormalities increase with increasing concentration of the teratogen.