Optimal chemical triploid induction in geoduck clams, Panopea abrupta, by 6-dimethylaminopurine

The development of geoduck culture techniques coupled with increased market demand during the past decade led to cultured intertidal geoduck beds, over which concerns have arisen regarding the potential genetic risk posed by the reproductive contribution of hatchery outplants to wild stocks. Although an ongoing study to determine the genetic stock structure of Puget Sound geoducks has yet to yield definitive results, sterile triploids would enable geoduck culture to proceed irrespective of any genetic differences found, and may increase rate of growth. At 15 °C and salinity of 30‰, we evaluated the suitability of cytochalasin B (CB) and 6-dimethylaminopurine (6-DMAP) for triploid induction in geoducks. Parallel tests of induction agent, start time, duration, and concentration were conducted on the same gamete pool. We found optimal triploid induction (92%) and suitable survivorship (30%) resulted from a 600 μM 6-DMAP treatment. This work enables the future examination of the efficacy of triploid induction for conferring sterility and increasing growth rate in this commercially valuable species.     

Classification of cassava into ‘bitter’ and ‘cool’ in Malawi: From farmers' perception to characterisation by molecular markers

Cassava roots, a major food in Africa, contain cyanogenic glucosides that may cause toxic effects. Malawian women farmers considered fields of seemingly similar cassava plants to be mixes of both ‘cool’ and ‘bitter’ cultivars. They regard roots from ‘cool’ cultivars as non-toxic. Roots of ‘bitter’ were considered to require extensive traditional processing done by women to be safe for consumption. But curiously, these women farmers preferred ‘bitter’ cultivars since toxicity confers protection against theft, which was a serious threat to the food security of their families. We studied how well these farmers comprehend the effects of genetic variations in cassava when dealing with cyanogenesis in this complex system. Using molecular markers we show that most plants farmers identified as belonging to a particular named cultivar had a genotype typical of that cultivar. Farmers' ethno-classification into ‘cool’ and ‘bitter’ cultivars corresponded to a genetic sub-division of the typical genotypes of the most common cultivars, with four-fold higher cyanogenic glucoside levels in the bitter cultivars. Examining morphology, farmers distinguished genotypes better than did the investigators when using a standard botanical key. Undoubtedly, these women farmers grasp sufficiently the genetic diversity of cassava with regard to cyanogenesis to simultaneously benefit from it and avoid its dangers. Consequently, acyanogenic cassava – the breeding of which is an announced good of some cassava genetic improvement programmes – is not a priority to these farmers. Advances in molecular genetics can help improve food supply in Africa by rapid micropropagation, marker assisted breeding and introduction of transgenic varieties, but can also help to elucidate tropical small-scale farmers' needs and skills. This revised version was published online in August 2006 with corrections to the Cover Date.     

Estimates of minimum viable population sizes for vertebrates and factors influencing those estimates

Population size is a major determinant of extinction risk. However, controversy remains as to how large populations need to be to ensure persistence. It is generally believed that minimum viable population sizes (MVPs) would be highly specific, depending on the environmental and life history characteristics of the species. We used population viability analysis to estimate MVPs for 102 species. We define a minimum viable population size as one with a 99% probability of persistence for 40 generations. The models are comprehensive and include age-structure, catastrophes, demographic stochasticity, environmental stochasticity, and inbreeding depression. The mean and median estimates of MVP were 7316 and 5816 adults, respectively. This is slightly larger than, but in general agreement with, previous estimates of MVP. MVPs did not differ significantly among major taxa, or with latitude or trophic level, but were negatively correlated with population growth rate and positively correlated with the length of the study used to parameterize the model. A doubling of study duration increased the estimated MVP by approximately 67%. The increase in extinction risk is associated with greater temporal variation in population size for models built from longer data sets. Short-term studies consistently underestimate the true variances for demographic parameters in populations. Thus, the lack of long-term studies for endangered species leads to widespread underestimation of extinction risk. The results of our simulations suggest that conservation programs, for wild populations, need to be designed to conserve habitat capable of supporting approximately 7000 adult vertebrates in order to ensure long-term persistence.     

Hemoxygenase-2 is an oxygen sensor for a calcium-sensitive potassium channel

Modulation of calcium-sensitive potassium (BK) channels by oxygen is important in several mammalian tissues, and in the carotid body it is crucial to respiratory control. However, the identity of the oxygen sensor remains unknown. We demonstrate that hemoxygenase-2 (HO-2) is part of the BK channel complex and enhances channel activity in normoxia. Knockdown of HO-2 expression reduced channel activity, and carbon monoxide, a product of HO-2 activity, rescued this loss of function. Inhibition of BK channels by hypoxia was dependent on HO-2 expression and was augmented by HO-2 stimulation. Furthermore, carotid body cells demonstrated HO-2-dependent hypoxic BK channel inhibition, which indicates that HO-2 is an oxygen sensor that controls channel activity during oxygen deprivation.     

The mTOR-regulated phosphoproteome reveals a mechanism of mTORC1-mediated inhibition of growth factor signaling

The mammalian target of rapamycin (mTOR) protein kinase is a master growth promoter that nucleates two complexes, mTORC1 and mTORC2. Despite the diverse processes controlled by mTOR, few substrates are known. We defined the mTOR-regulated phosphoproteome by quantitative mass spectrometry and characterized the primary sequence motif specificity of mTOR using positional scanning peptide libraries. We found that the phosphorylation response to insulin is largely mTOR dependent and that mTOR exhibits a unique preference for proline, hydrophobic, and aromatic residues at the +1 position. The adaptor protein Grb10 was identified as an mTORC1 substrate that mediates the inhibition of phosphoinositide 3-kinase typical of cells lacking tuberous sclerosis complex 2 (TSC2), a tumor suppressor and negative regulator of mTORC1. Our work clarifies how mTORC1 inhibits growth factor signaling and opens new areas of investigation in mTOR biology.     

Mineralized,obstructive cardiac myxoma with chondroid differentiation in a cocker spaniel

A 12-year-old castrated male cocker spaniel dog was referred for evaluation of signs consistent with right-sided heart failure. Thoracic radiography revealed mineralization in the region of the right atrium. Echocardiography identified a mass partially filling the right atrium and right ventricle and obstructing flow through the right heart. These findings were confirmed at necropsy and histopathologic features were consistent with myxoma with chondroid differentiation.     

Nerve insensitivity resistance to cypermethrin in larvae of the tobacco budworm Heliothis virescens from USA cotton field populations

Spontaneous neuronal activity was recorded from the peripheral nerves of third-instar larvae of strains of Heliothis virescens (F.) obtained directly from cotton fields in the USA. Following a control period the preparations were exposed to increasing concentrations of cis-cypermethrin in a cumulative dose-response assay. A positive response was defined as an increase of at least five-fold in the rate of neuronal activity over that seen during the control period. Up to 35 individuals of each strain were assayed and the responses used to construct a phenotypic profile categorising the individuals from nerve-susceptible to highly nerve-insensitive. An EC₅₀ for the action of cis-cypermethrin was also obtained. There was a positive, significant correlation between non-synergisable resistance to cypermethrin and nerve insensitivity as defined in the neurophysiological assay. It was shown that nerve insensitivity to cypermethrin increased throughout the cotton-growing season.     

Congenital internal hydrocephalus in a quarter horse foal

Since the normal absorption of CSF occurs in the cerebral veins and venous sinuses, any obstruction to the normal flow and absorption of CSF will result in accumulation of CSF central to the site of obstruction. Such accumulation within the cranium is defined as hydrocephalus.A foal was presented with an enlarged and an abnormally-shaped skull, but with normal behavior. The filly's condition deteriorated. Radiographs showed a domeshaped cranial vault with compression of the frontal sinus region. Massive hydrocephalus with little normal cerebral tissue left was diagnosed with ultrasound.Surgery was attempted to relieve the pressure. Eventually the foal was euthanized. Post-mortem confirmed the radiographic and ultrasound diagnosis. Since there was a lack of demonstrable obstruction, the authors suspected the foal had suffered from the Arnold-Chiari syndrome.     

ULTRASONOGRAPHIC FINDINGS IN CHOLECYSTOKININ-INDUCED PANCREATITIS IN DOGS

Pancreatitis can be induced in dogs by intravenous infusion of supraphysiologic doses of synthetic cholecystokinin octapeptide (CCK-8). Eight anesthetized female beagles were given either CCK-8 or saline in a randomized, blinded fashion and had abdominal ultrasonography to study the development of pancreatic lesions. Pancreatic lesions were apparent 2 hours after the start of CCK-8 infusion and included swelling, interlobular and subcapsular fluid accumulation and patchy hypoechogenicity of the gland parenchyma. CCK-8 had a variable effect on gallbladder emptying. No signs of biliary obstruction or duodenal lesions were identified. Dogs given CCK-8 had severe edematous pancreatitis at necropsy six hours after the start of the infusion. Compared to the oleic acid model of pancreatitis, CCK-8 infusion induces a rapid onset of pancreatitis and an ultrasonographic appearance that reflects diffuse edema of the gland. The short time-scale of the experiment may account for the relative absence of secondary lesions affecting the biliary tract or duodenum compared to the naturally-occurring disease.