Barbara Stay

Structure and regulation of the corpus allatum

Publisher Summary This chapter discusses the structure and regulation of the corpus allatum. The corpora allata (CA) are endocrine glands in the posterior regions of the head, or in rare instances in the thorax, which are closely associated with the stomatogastric nervous system. This chapter focuses on the regulation of the CA. It also describes the embryology, innervations, and the relationships of the structure, particularly the ultrastructure, to its synthetic activity. The characteristic shape of the CA is ovoid to round but they may be elongate as in large larvae and adults of Libellula depressa. The size of the glands is frequently about the diameter of the aorta or smaller; however, there is much variation among species and even within a species, size differs with age, sex, polymorphism, and the activity cycle of the glands. Although only one type of glandular cell occurs in the CA, there are a variety of types of CA with respect to the number of cells per gland and the relative size of the cells. The CA are surrounded by a continuous noncellular basal lamina, roughly 0.1-1 μ m thick. This material occasionally projects between two glandular cells into the interior of the gland, forming trabeculae that may accompany nerves and trachea.

Allatostatins: Identification, Primary Structures, Functions and Distribution

Publisher Summary This chapter focuses on the neuropeptides of known amino acid sequence that inhibit juvenile hormone (JH) production by the corpora allata (CA). During insect development, juvenile hormone (JH) maintains the juvenile form and metamorphosis to the adult form appears to require a reduced titre of JH. The regulation of JH production involves many factors, both extrinsic and intrinsic. With the discovery of at least 30 different Diploptera punctata allatostatin-like peptides in several species of insect, most showing the characteristic pentapeptide Tyr-Xaa-Phe-Gly-Leu-NH2 carboxyl (C)-terminus, it is now clear that these allatostatins represent a unique family of neuropeptides that probably serve several different functions in insects and related arthropods. The occurrence of multiple allatostatin peptides has prompted the search for receptors of important peptides. The neurosecretory cells producing allatostatins are identified immunohistochemically with antibodies produced against synthetic allatostatins. The immunocytochemical localization of allatostatin-like peptides in interneurons of the central nervous system; in neurons that innervate visceral muscle and glands other than the corpora allata, neurohaernal organs; and in midgut cells suggests that allatostatins are multifunctional neuropeptides even though inhibition of JH synthesis by corpora allata in vitro was the only bioassay utilized in their isolations. The coding region that specifies an allatostatin gene in Diploptera punctata was identified and isolated by polymerase chain reaction (PCR). Study of the regulation of allatostatin release is possible now, because the peptides have been identified and sensitive methods have been developed to quantitate them. The search for neuropeptide regulators of JH synthesis by the CA has led to the identification of a peptide from the moth Munducu sexfa and quite a different family of peptides from the cockroaches, Diploptera punctata and Periplaneta americana.

Control of juvenile hormone biosynthesis during the reproductive cycle of a viviparous cockroach: I. Activation and inhibition of corpora allata

Abstract An in vitro radiochemical assay has been used to determine the juvenile hormone (JH) synthetic capacity of denervated and transplanted corpora allata (CA) of female Diploptera punctata . CA maintained in vitro over a 24-hr period do not increase their rate of JH synthesis whether taken from females in which they would undergo a dramatic increase in vivo (just before vitellogenesis) or from females in which CA synthesize JH at a low rate for an extended period (as in pregnancy). However, when CA are denervated and allowed to remain in vivo , a normal cycle of JH synthesis is observed in mated females. In virgin females, which do not normally mature eggs, the denervation mimics mating in that the CA undergo a synthetic cycle and oocytes are matured. Denervation of CA of young pregnant females (16% gestation) does not result in an immediate cycle of synthesis similar to that of mated females, nor do 0-day CA transplanted to allatectomized pregnant females exhibit such a cycle. However, inactive CA from the pregnant females transplanted to allatectomized 0-day animals promptly undergo a cycle of JH synthesis with an associated maturation of oocytes. From these results it is concluded that the integrity of the nerves of CA is required for inhibition of synthetic activity, whereas some factor in the hemolymph, not present in pregnant females, is responsible for activation and maintenance of the JH synthetic cycle.

Corpus allatum activity in vitro during the reproductive cycle of the viviparous cockroach, Diploptera punctata (Eschscholtz).

Isolated pairs of corpora allata (CA) from the viviparous cockroach, Diploptera punctata have been shown to synthesize and release C16JH at a linear rate for at least 5 hr. No storage of C16JH has been observed at any time during the first oviposition cycle. It is suggested that rate limitation in JH biosynthesis does not occur at the terminal enzymic stage because the immediate precursor, methyl farnesoate, does not accumulate at any level of CA activity. It is concluded that the short-term incubation procedures employed represent an accurate assessment of CA activity in vivo. The synthesis and release of C16JH by CA has been followed during the first oviposition cycle. High rates of release of JH were observed during rapid oocyte growth—CA became highly active over a 24 hr period as the oocytes were entering vitellogenesis. An analysis of CA activity relative to oocyte length revealed that the release rate of C16JH was highest when oocyte length was in the range 1.0–1.6 mm. However, it was not possible to ascertain if vitellogenesis was initiated before or after the increase in the JH release rate. C16JH synthesis of 40 pmol hr−1 is the highest mean rate yet reported for an insect.

Hormonal regulation of behavioural development in the honey bee is based on changes in the rate of juvenile hormone biosynthesis

Abstract In the adult worker honey bee (Apis mellifera L.), increases in the haemolymph titre of juvenile hormone underlie behavioural development, from nest duties to foraging. However, the physiological basis of juvenile hormone titre regulation was unknown. Using a radiochemical assay for juvenile hormone biosynthesis in vitro, we demonstrate that differences in juvenile hormone titres among bees performing different age-dependent tasks are a consequence of changes in rates of hormone synthesis by the corpora allata. Rates of juvenile hormone biosynthesis were low in newly emerged bees, 7–9-day-old nurse bees, and 14–15-day-old bees collected from the nest periphery, and high in foragers. Rates of biosynthesis were highly correlated with haemolymph titres of juvenile hormone measured in the same individuals. Corpora allata contained mostly methyl farnesoate, the immediate precursor of juvenile hormone, and released principally juvenile hormone III into the incubation medium, indicating no appreciable hormone storage. We also report similarities and differences in parameters of juvenile hormone biosynthesis between nurse bees and foragers that were found during the course of a detailed characterization of the radiochemical assay for adult worker honey bees. These results, coupled with the fact that it is possible to measure rates of juvenile hormone biosynthesis from individual bees, indicate that the radiochemical assay will be useful in further studies of hormonal regulation of bee behaviour.

Allatostatin-immunoreactive neurons projecting to the corpora allata of adult Diploptera punctata

SummaryA monoclonal antibody against allatostatin I was used to demonstrate the allatostatin-immunoreactive pathways between the brain and the corpus cardiacum-corpus allatum complex in the adult cockroach Diploptera punctata. The antibody was two to three orders of magnitude more sensitive to allatostatin I than to the other four known members of the allatostatin family. Whole and sectioned brains in which immunoreactivity was localized with horseradish peroxidase-H2O2-diaminobenzidine reaction showed strongly immunoreactive cells in the pars lateralis of the brain with axons leading to and arborizing in the corpus cardiacum and the corpus allatum. Although many neurosecretory cells of the pars intercerebralis project to the corpora allata only, four strongly immunoreactive cells were evident here (two pairs on either side), and these did not project to the corpus cardiacum and corpus allatum but rather terminated within the protocerebrum in areas in which lateral cells also formed arborizations. Immunoreactivity was found in many other cells in the brain, especially in the tritocerebrum.

A review of the role of neurosecretion in the control of juvenile hormone synthesis: a tribute to Berta Scharrer

In the 1950s, Berta Scharrer predicted that neurosecretions from the brain regulated corpus allatum activity based upon the observation of the change in localization of neurosecretory material in the brain and change in gland activity after severance of nerves between the brain and corpus allatum. Isolation and characterization of neuropeptide regulators of juvenile hormone production by the corpora allata in the late 1980s has confirmed this prediction. Both a stimulatory allatotropin and an inhibitory allatostatin have been isolated from moth brains. Two families of allatostatins, both quite different from each other and that of moths, have been isolated from cockroaches and crickets. The wide distribution of these peptides in the nervous system, in nerves to visceral muscle, in endocrine cells of the midgut and in blood cells, indicate multifunctions in the insects in which they are allatoregulatory. Some of these other functions have been demonstrated in these insects and in insects in which these neuropeptides occur but do not act as corpus allatum regulators. For the latter group, the neuropeptide regulators of the corpora allata have yet to be isolated. The families of neurosecretory regulators will continue to grow.

Feedback control of juvenile hormone synthesis in cockroaches: possible role for ecdysterone.

Inactive female corpora allata implanted into adult males become active and continue to synthesize juvenile hormone at high rates. However, when an ovary is implanted together with the corpora allata, rates of juvenile hormone synthesis decline as the oocytes complete maturation. Injections of ecdysterone mimic the effect of an implanted ovary.

Two new allatostatins from the brains of Diploptera punctata

Allatostatins VI and VII have been isolated from saline extracts of the brain of the viviparous cockroach Diploptera punctata. Active fractions, obtained by successive reverse-phase high pressure liquid chromatography separations, inhibited juvenile hormone (JH) III production by corpora allata (CA) in vitro. The primary structures, Y-P-Q-E-H-R-F-S-F-G-L-amide (VI) and D-G-R-M-Y-S-F-G-L-amide (VII), clearly identify them as members of a family of D. punctata allatostatins, five of which have been identified previously and shown to have F-G-L-amide at the C terminus. Synthetic allatostatins VI and VII coeluted with the native allatostatins on two successive high pressure liquid chromatography separations. Allatostatins VI and VII have the same capacity to inhibit JH production by CA of 2 day virgin females as does allatostatin I, previously shown to be a potent inhibitor similar in activity to allatostatin V. Allatostatins VI and VII also resemble the other allatostatins in their ability to affect both larval and adult CA, in the reversibility of their effect, and in the abolition of their effect by addition of farnesoic acid (a late precursor of JH) to CA in vitro.

Control of juvenile hormone biosynthesis during the reproductive cycle of a viviparous cockroach II. Effects of unilateral allatectomy, implantation of supernumerary corpora allata, and ovariectomy

Using a direct radiochemical assay, the effects of implantation of supernumerary corpora allata (CA), unilateral allatectomy, and ovariectomy on rates of juvenile hormone (JH) biosynthesis by the CA and on the duration of the gonotrophic cycle have been investigated during the first gonotrophic cycle of the viviparous cockroach Diploptera punctata. Implantation of supernumerary CA decreased the duration of the gonotrophic cycle and had no effect on JH biosynthesis by denervated host CA or by implanted glands. Thus, there appears to be no evidence for a compensatory response reducing JH synthesis under these conditions of high JH titers. Unilateral allatectomy, however, resulted in compensation by the remaining CA: a single CA synthesized the same quantity of JH during the gonotrophic cycle as a pair of CA although maximum rates of synthesis were delayed by 1 day. Accordingly, the gonotrophic cycle is slightly longer in duration in unilaterally allatectomized animals. Ovariectomy either as nymphs or young adults depressed the rate of JH synthesis by the CA. A model for the regulation of JH biosynthesis by the corpora allata in cockroaches is proposed.