@article {6883, title = {The developmental control of size in insects.}, journal = {Wiley Interdisciplinary Reviews: Developmental Biology}, volume = {3}, year = {2014}, month = {2014 Jan/Feb}, pages = {113-34}, abstract = {

The mechanisms that control the sizes of a body and its many parts remain among the great puzzles in developmental biology. Why do animals grow to a species-specific body size, and how is the relative growth of their body parts controlled to so they grow to the right size, and in the correct proportion with body size, giving an animal its species-characteristic shape? Control of size must involve mechanisms that somehow assess some aspect of size and are upstream of mechanisms that regulate growth. These mechanisms are now beginning to be understood in the insects, in particular in Manduca sexta and Drosophila melanogaster. The control of size requires control of the rate of growth and control of the cessation of growth. Growth is controlled by genetic and environmental factors. Insulin and ecdysone, their receptors, and intracellular signaling pathways are the principal genetic regulators of growth. The secretion of these growth hormones, in turn, is controlled by complex interactions of other endocrine and molecular mechanisms, by environmental factors such as nutrition, and by the physiological mechanisms that sense body size. Although the general mechanisms of growth regulation appear to be widely shared, the mechanisms that regulate final size can be quite diverse. WIREs Dev Biol 2014, 3:113{\textendash}134. doi: 10.1002/wdev.124

}, issn = {1759-7684}, doi = {10.1002/wdev.124}, author = {Nijhout, H. Frederik and Riddiford, Lynn M and Mirth, Christen and Shingleton, Alexander W and Suzuki, Yuichiro and Callier, Viviane} } @article {6383, title = {A molt timer is involved in the metamorphic molt in Manduca sexta larvae.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {110}, year = {2013}, month = {2013 Jul 30}, pages = {12518-25}, abstract = {

Manduca sexta larvae are a model for growth control in insects, particularly for the demonstration of critical weight, a threshold weight that the larva must surpass before it can enter metamorphosis on a normal schedule, and the inhibitory action of juvenile hormone on this checkpoint. We examined the effects of nutrition on allatectomized (CAX) larvae that lack juvenile hormone to impose the critical weight checkpoint. Normal larvae respond to prolonged starvation at the start of the last larval stage, by extending their subsequent feeding period to ensure that they begin metamorphosis above critical weight. CAX larvae, by contrast, show no homeostatic adjustment to starvation but start metamorphosis 4 d after feeding onset, regardless of larval size or the state of development of their imaginal discs. By feeding starved CAX larvae for various durations, we found that feeding for only 12-24 h was sufficient to result in metamorphosis on day 4, regardless of further feeding or body size. Manipulation of diet composition showed that protein was the critical macronutrient to initiate this timing. This constant period between the start of feeding and the onset of metamorphosis suggests that larvae possess a molt timer that establishes a minimal time to metamorphosis. Ligation experiments indicate that a portion of the timing may occur in the prothoracic glands. This positive system that promotes molting and the negative control via the critical weight checkpoint provide antagonistic pathways that evolution can modify to adapt growth to the ecological needs of different insects.

}, issn = {1091-6490}, doi = {10.1073/pnas.1311405110}, author = {Suzuki, Yuichiro and Koyama, Takashi and Hiruma, Kiyoshi and Riddiford, Lynn M and Truman, James W} } @article {2502, title = {Larval leg integrity is maintained by distal-less and is required for proper timing of metamorphosis in the flour beetle, tribolium castaneum.}, journal = {Developmental Biology}, volume = {326}, year = {2009}, month = {2009 Feb 1}, pages = {60-7}, abstract = {

The dramatic transformation from a larva to an adult must be accompanied by a coordinated activity of genes and hormones that enable an orchestrated transformation from larval to pupal/adult tissues. The maintenance of larval appendages and their subsequent transformation to appendages in holometabolous insects remains elusive at the developmental genetic level. Here the role of a key appendage patterning gene Distal-less (Dll) was examined in mid- to late-larval stages of the flour beetle, Tribolium castaneum. During late larval development, Dll was expressed in appendages in a similar manner as previously reported for the tobacco hornworm, Manduca sexta. Removal of this late Dll expression resulted in disruption of adult appendage patterning. Intriguingly, earlier removal resulted in dramatic loss of structural integrity and identity of larval appendages. A large amount of variability in appendage morphology was observed following Dll dsRNA injection, unlike larvae injected with dachshund dsRNA. These Dll dsRNA-injected larvae underwent numerous supernumerary molts, which could be terminated with injection of either JH methyltransferase or Methoprene-tolerant dsRNA. Apparently, the partial dedifferentiation of the appendages in these larvae acts to maintain high JH and, hence, prevents metamorphosis.

}, keywords = {Animals, Biological, Double-Stranded, Extremities, Homeodomain Proteins, Larva, Metamorphosis, Methoprene, RNA, Transcription Factors, Tribolium}, issn = {1095-564X}, doi = {10.1016/j.ydbio.2008.10.022}, author = {Suzuki, Yuichiro and Squires, Diego C and Riddiford, Lynn M} } @article {2505, title = {The role of Broad in the development of Tribolium castaneum: implications for the evolution of the holometabolous insect pupa.}, journal = {Development (Cambridge, England)}, volume = {135}, year = {2008}, month = {2008 Feb}, pages = {569-77}, abstract = {

The evolution of complete metamorphosis in insects is a key innovation that has led to the successful diversification of holometabolous insects, yet the origin of the pupa remains an enigma. Here, we analyzed the expression of the pupal specifier gene broad (br), and the effect on br of isoform-specific, double-stranded RNA-mediated silencing, in a basal holometabolous insect, the beetle Tribolium castaneum. All five isoforms are weakly expressed during the penultimate instar and highly expressed during the prepupal period of the final instar. Application of hydroprene, a juvenile hormone analog, during the penultimate instar caused a repeat of the penultimate br expression patterns, and the formation of supernumerary larvae. Use of dsRNA against the br core region, or against a pair of either the br-Z2 or br-Z3 isoform with the br-Z1 or br-Z4 isoform, produced mobile animals with well-differentiated adult-like appendages, but which retained larval-like urogomphi and epidermis. Disruption of either the br-Z2 or the br-Z3 isoform caused the formation of shorter wings. Disruption of both br-Z1 and br-Z4 caused the appearance of pupal traits in the adults, but disruption of br-Z5 had no morphological effect. Our findings show that the br isoform functions are broadly conserved within the Holometabola and suggest that evolution of br isoform expression may have played an important role in the evolution of the pupa in holometabolous insects.

}, keywords = {Animals, Biological Evolution, Developmental, Double-Stranded, Fatty Acids, Gene Expression Profiling, Gene Expression Regulation, Genes, Insect, Insect Proteins, Larva, Phenotype, Protein Isoforms, Pupa, RNA, RNA Interference, Tribolium, Unsaturated}, issn = {0950-1991}, doi = {10.1242/dev.015263}, author = {Suzuki, Yuichiro and Truman, James W and Riddiford, Lynn M} }