Current evidence indicates that methyl farnesoate is the crustacean equivalent of the juvenile hormones of insects. This putative hormone is produced by the mandibular organs and is negatively regulated by a neuropeptide produced and secreted by the X-organ-sinus gland complex of the eyestalk. To identify this neuropeptide, a bioassay was developed which measures the inhibition of methyl farnesoate synthesis by mandibular organs exposed to fractionated sinus gland extracts from the crab, Cancer pagurus. Two neuropeptides, named mandibular organ-inhibiting hormones (MOIH-1 and -2) repressed methyl farnesoate synthesis. MOIH-1 was fully sequenced by automated Edman degradation of endoproteinase-derived fragments and further characterized by mass spectrometry. This peptide consisted of 78 residues (M r 9235.6), with unblocked termini and three intrachain disulfide bridges. MOIH-2 appeared to be almost identical to MOIH-1 with the exception of a Gln for Lys substitution at position 33. Comparison with previously sequenced crustacean neuropeptides shows that these MOIHs are members of the ever expanding crustacean hyperglycemic hormone family, with significant sequence similarity to molt-inhibiting hormones (MIHs). It is possible that these two structurally similar peptides (MIH, MOIH) may control mutually exclusive physiological phenomena (somatic and gonadal growth), suggesting a complex hormonal integration of these processes in crustaceans.

The Shaugh Moor project is concerned with an area of moorland in south Dartmoor north-east and north respectively of the villages of Shaugh Prior and Wotter (fig. 1). The physical threat to the evidence for settlement and land-use caused by the operations of the China Clay industry involved the Central Excavation Unit of the Department of the Environment from 1976 in a programme of survey, excavation and environmental studies related to the settlements, land boundaries, burial mounds and ceremonial structures that are to be found on this piece of moorland. The background to the project and its preliminary research strategy have been outlined in Paper I (Wainwright et al. 1979) and this publication describes the investigation of a stone-walled enclosure surrounding houses and other structures that was totally excavated in 1977 and 1978. Subsequent papers will describe the related archaeological and scientific investigations into the past environment and land-use of this block of moorland and its adjacent region.

Viewed from the south Devon littoral with its series of good harbours the dark bulk of Dartmoor is clearly visible across the flat coastal plain. It is the largest of the five granite masses that provide a spine to the south-west English peninsula (Dartmoor, Bodmin Moor, Hensbarrow, Carnmenellis and Penwith) that were formed by the consolidation of molten material. The 500 square kilometres of the Moor form an undulating upland up to 600 m OD on the north-east side, where the greatest elevations occur. In the southern parts of the Moor the rolling tableland is 300 m to 420 m high—modern cultivation tends to cease at the 300 m contour, that is broken by numerous upland valleys and the eroded remains of tors. Today this expanse of moorland is bleak and treeless except in river valleys at the rim of the granite escarpment, although patches of contorted oak woodland survive at Piles' Wood on the River Erme, Wistman's Wood on the West Dart and Black Tor Beare on the West Okement. Pollen analyses have shown, however, that up to a height of about 360 m Dartmoor was probably covered by a deciduous forest dominated by oak that was gradually eroded by climatic trends and human activity (e.g. Simmons, 1969). It is from this central mass that the rivers of south Devon diverge. The wide upland valleys of the Tavy, Plym, Yealm, Erme, Avon and Dart plunge through characteristic deep wooded gorges near the southern granite escarpment into the South Hams and around this border modern settlement—numerous villages and a few towns are situated.

No abstract

The neuropeptide mandibular organ (MO)-inhibiting hormone (MO-IH), synthesized and secreted from the X-organ-sinus-gland complex of the eyestalk, regulates the biosynthesis of the putative crustacean juvenile hormone, methyl farnesoate (MF). Using radiolabelled acetate as a precursor for isoprenoid biosynthesis, farnesoic acid (FA), farnesol, farnesal, MF and geranyl geraniol were detected in MOs cultured for 24 h. Treatment of MOs with extract of sinus gland inhibited the final step of biosynthesis of MF, catalysed by FA O-methyltransferase. Additionally, treatment of MOs with purified MO-IH exhibited a dose-dependent inhibition of this final step of MF synthesis. The extent of this inhibition was dependent on the ovary stage of the MO-donor animal, being maximal in MOs from animals in the early stages of ovarian development. Assay of FA O-methyltransferase activity, using [3H]FA in the presence of S-adenosyl-l-methionine, demonstrated that the enzyme was located in the cytosolic fraction of MOs and was inhibited by incubation of MOs with MO-IH prior to preparation of subcellular fractions. For cytosolic preparations taken from vitellogenic animals, both Vmax and Km were appreciably lower than for those taken from non-vitellogenic animals. Conversely, eyestalk ablation of early-vitellogenic animals, which removes the source of MO-IH in vivo, resulted in enhancement of the cytosolic FA O-methyltransferase activity. Although both Vmax and Km show an appreciable increase upon eyestalk ablation, the increased enzyme activity is probably reflected by the fact that Vmax/Km (an approximate indication of kcat) has increased 5-fold. The combined evidence demonstrates that MO-IH inhibits FA O-methyltransferase, the enzyme which catalyses the final step of MF biosynthesis in MOs.