Hormonal Control Of Development Research Articles

More similar than you think: Frog metamorphosis as a model of human perinatal endocrinology

Hormonal control of development during the human perinatal period is critically important and complex with multiple hormones regulating fetal growth, brain development, and organ maturation in preparation for birth. Genetic and environmental perturbations of such hormonal control may cause irreversible morphological and physiological impairments and may also predispose individuals to diseases of adulthood, including diabetes and cardiovascular disease. Endocrine and molecular mechanisms that regulate perinatal development and that underlie the connections between early life events and adult diseases are not well elucidated. Such mechanisms are difficult to study in uterus-enclosed mammalian embryos because of confounding maternal effects. To elucidate mechanisms of developmental endocrinology in the perinatal period, Xenopus laevis the African clawed frog is a valuable vertebrate model. Frogs and humans have identical hormones which peak at birth and metamorphosis, have conserved hormone receptors and mechanisms of gene regulation, and have comparable roles for hormones in many target organs. Study of molecular and endocrine mechanisms of hormone-dependent development in frogs is advantageous because an extended free-living larval period followed by metamorphosis (1) is independent of maternal endocrine influence, (2) exhibits dramatic yet conserved developmental effects induced by thyroid and glucocorticoid hormones, and (3) begins at a developmental stage with naturally undetectable hormone levels, thereby facilitating endocrine manipulation and interpretation of results. This review highlights the utility of frog metamorphosis to elucidate molecular and endocrine actions, hormone interactions, and endocrine disruption, especially with respect to thyroid hormone. Knowledge from the frog model is expected to provide fundamental insights to aid medical understanding of endocrine disease, stress, and endocrine disruption affecting the perinatal period in humans.

The role of 20-hydroxyecdysone signaling in Drosophila pupal metabolism

In holometabolous insects, the steroid hormone 20-hydroxyecdysone (20E), in coordination with juvenile hormone, regulates the major developmental events that promote larval development and the transition from the larval to the pupal stage. Intimately entwined with the hormonal control of development is the control of larval growth and the acquisition of energy stores necessary for the development of the non-feeding pupa and immature adult. Studies of the coordination of insect development and growth have suggested that the larval fat body plays a central role in monitoring animal size and nutritional status by integrating 20E signaling with the insulin signaling pathway. Previous studies have shown that tissue-specific loss of 20E signaling in the fat body causes pupal lethality (Cherbas et al., 2003). Because the fat body is the major organ responsible for nutrient homeostasis, we hypothesized that the observed pupal mortality is due to a metabolic defect. In this paper we show that disruption of 20E signaling in the fat body does not disrupt nutrient storage, animal size at pupariation, or nutrient utilization. We conclude that 20E signaling in the fat body is not necessary for normal pupal metabolism.

Cloning and characterization of an ecdysone receptor cDNA from Locusta migratoria

To facilitate studies on the hormonal control of development in the migratory locust, Locusta migratoria, we have undertaken the cloning of cDNAs for nuclear hormone receptors. Sequences obtained by polymerase chain reaction (PCR) showed homology with receptor family members including the ecdysteroid receptor (EcR). A cDNA clone corresponding to the EcR fragment includes an open reading frame of 1622 nucleotides, predicting a 59 kDa protein showing clear homology with EcRs and distinct from other classes of nuclear receptors. Northern analysis revealed a major transcript of 9.2 kb. In fifth instar fat body, the transcript was most abundant at the end of the instar when ecdysone titres are highest. There was no obvious evidence of EcR regulation by a juvenile hormone analog. Although its role in development may be similar, the locust ecdysone receptor (LmEcR) is divergent from EcRs characterized from insects belonging to the dipteran and lepidopteran orders, presumably reflecting the more ancestral sequence in the relatively primitive locust.

Insect tissue culture systems: models for study of hormonal control of development

The regulation of growth and development of insects is under endocrine control and involves both juvenile hormones and ecdysteroids. Neuropeptides are master regulators which control the secretion of these hormones. Most experiments in insect endocrinology have been conducted in vivo, but tissue culture methodology is playing an increasing role due to the great interest in simpler model systems for the study of complex processes that occur in vivo. The availability of appropriate media has allowed the culture of a variety of insect organs and cell lines of defined origin which have kept certain properties of the parent tissues. Tissue culture approaches have been useful for studying hormonal control of morphogenetic processes. Cell lines are particularly suited to the study of hormonally regulated mechanisms of macromolecular biosynthesis and gene expression. Thus, the value of in vitro analysis in studies of regulation of hormone production is now recognized. Results obtained from tissue culture allow more precise definition of the hormonal requirements of insect cells and tissues for growth and differentiation and might make possible the discovery of new growth regulators.