Stephen S. Tobe

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.

A rapid partition assay for routine analysis of juvenile hormone release by insect corpora allata

A partition assay is described which allows a rapid determination of juvenile hormone release by insect corpora allata. Newly synthesized and released methyl-labeled C16 juvenile hormone is quantitatively extracted into an isooctane phase, whereas precursor methyl-labeled l-methionine remains in the incubation medium. When used in conjunction with appropriate blank assays, this method offers both accuracy and speed necessary for routine analysis of corpora allata activity.

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.

Allatostatins: A Growing Family of Neuropeptides with Structural and Functional Diversity

Abstract: The high degree of conservation of the core sequence of the “cockroach‐types” of AST and their widespread distribution suggest that they should be considered a ubiquitous family of peptides within the invertebrates, regulating a range of important physiological processes. These functional processes, by either neural or humoral routes of action, include the inhibition of endocrine function, interneuronal functions, neuromodulatory roles, myotropic and myoendocrine roles, and direct action on biosynthetic pathways. The myomodulatory function appears to be conserved through evolutionary time, whereas the JH inhibitory activity appears to be confined to specific orders. This suggests that the myomodulatory role was the more ancestral of these two particular functions. Certainly, further purification and gene cloning as a means to precursor identification and functional analysis will be a prerequisite to understanding the diverse functions of this peptide family.

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.

The effect of the thirteen Dip-allatostatins on myogenic and induced contractions of the cockroach (Diploptera punctata) hindgut

Abstract The Dip-allatostatins are a group of 13 neuropeptides, ranging in size from 6 to 18 amino acids, identified from a cloned cDNA sequence of Diploptera punctata . All 13 Dip-allatostatins inhibited both myogenic and proctolin-induced contractions of the hindgut of D. punctata . Dip-allatostatins were capable of reducing a 5 × 10 −6 M proctolin-induced contraction in a dose-dependent manner, with ED 50 values ranging from 1.7 × 10 −7 M for Dip-allatostatin 7 to greater than 1.3 × 10 −5 M for Dip-allatostatin 12. The effects of the Dip-allatostatins were reversible upon washing with saline. The free carboxylic acid (non-amidated) form of Dip-allatostatin 11, callatostatin 3 and callatostatin 5 showed a loss of inhibitory activity. In contrast to the inhibitory actions of the Dip-allatostatins on hindgut contractions, selected Dip-allatostatins (Dip-allatostatins 4, 6, 7, 10, 12), at concentrations ranging from 10 −7 M to 2 × 10 −5 M, did not alter the frequency or amplitude of myogenic contractions or inhibit proctolin-induced contractions of the cockroach oviduct muscle. Dip-allatostatins (Dip-allatostatins 1, 2, 4, 5, 6, 7) also had no effect on either myogenic or proctolin-induced contractions of the oviduct of Locusta migratoria .

Effects of an allatostatin and a myosuppressin on midgut carbohydrate enzyme activity in the cockroach Diploptera punctata

Neuropeptides of the cockroach allatostatin (AST) family are known for their ability to inhibit the production of juvenile hormone by the corpora allata of cockroaches. Since their discovery, they have also been shown to modulate myotropic activity in a range of insect species as well as to act as neurotransmitters in Crustaceans and possibly in insects. The midgut of cockroaches contains numerous endocrine cells, some of which produce AST whereas others produce the FMRFamide-related peptide, leucomyosuppressin (LMS). We have determined if ASTs and LMS are also able to influence carbohydrate-metabolizing enzyme activity in the midgut of the cockroach, Diploptera punctata. Dippu-AST 7 stimulates activity of both invertase and alpha-amylase in a dose-dependent fashion in the lumen contents of ligatured midguts in vitro, but not in midgut tissue, whereas the AST analog AST(b)phi2, a cyclopropyl-ala, hydrocinnamic acid analog of Dippu-AST 6, has no effect. Leucomyosuppressin also stimulates enzyme activity in lumen contents only, although the EC50 is considerably greater than for Dippu-AST. Dippu-AST is also able to inhibit proctolin-induced contractions of midgut muscle, and this action had already been described for LMS [18]. Thus, in this organ, AST and LMS have at least two distinct physiological effects.

Crustacean neuropeptide genes of the CHH/MIH/GIH family: implications from molecular studies.

The crustacean eyestalk CHH/MIH/GIH gene family represents a unique group of neuropeptide originally identified in crustaceans. These neuropeptides shared a high degree of amino acid identity, and the conservation of cysteine residues at the same relative positions. Based on their biological, biochemical, and molecular properties, they can be divided into the CHH and MIH subtypes with two major members in each subtype. In the shrimp, the CHH-subtypes can be divided into two forms (CHH-A and CHH-B). The CHH-A gene also comprises several isoforms which shared a high overall sequence identity. Although the MIH subtypes are postulated to have evolved from the CHH subtypes, the number of major MIH subtypes in each species has yet to be confirmed. While most of the genes consist of the basic plan of three exons and two introns, other alternative spliced variants have recently been described. Moreover, these alternative forms are usually expressed in non-eyestalk tissues. These findings suggest that these neuropeptides may have a broader spectrum of functions in crustaceans. The results from phylogenetic analysis suggest that the evolution of this group of neuropeptides occurs in a manner similar is to the gene duplication and mutation events hypothesized for the origin of the prolactin and growth hormone gene family of the vertebrate pituitary system.