The association between food desert severity, socioeconomic status, and metabolic state during pregnancy in a prospective longitudinal cohort

Poor metabolic health during pregnancy is associated with health concerns for pregnant individuals and their offspring. Lower socioeconomic status (SES) is one risk factor for poor metabolic health, and may be related to limited access to healthful and affordable foods (e.g., living in a food desert). This study evaluates the respective contributions of SES and food desert severity on metabolic health during pregnancy. The food desert severity of 302 pregnant individuals was determined using the United States Department of Agriculture Food Access Research Atlas. SES was measured using total household income adjusted for household size, years of education, and amount of reserve savings. Information about participants' glucose concentrations one hour following an oral glucose tolerance test during the second trimester was extracted from medical records and percent adiposity during the second trimester was assessed using air displacement plethysmography. Information about participants' nutritional intake during the second trimester was obtained by trained nutritionists via three unannounced 24-h dietary recalls. Structural equation models showed that lower SES predicted higher food desert severity (β = - 0.20, p = 0.008) and higher adiposity (β = - 0.27, p = 0.016) and consumption of a more pro-inflammatory diet (β = - 0.25, p = 0.003) during the second trimester of pregnancy. Higher food desert severity also predicted higher percent adiposity during the second trimester (β = 0.17, p = 0.013). Food desert severity significantly mediated the relationship between lower SES and higher percent adiposity during the second trimester (βindirect = - 0.03, 95% CI [- 0.079, - 0.004]). These findings indicate that access to healthful and affordable foods is a mechanism by which SES contributes to adiposity during pregnancy and may inform interventions intended to improve metabolic health during pregnancy.

Self-selected meal composition alters the relationship between same-day caloric intake and appetite scores in humans during a long-term ad-libitum feeding study

PURPOSE

To determine the effect of an off-protocol meal during a long-term ad libitum feeding study on changes in total caloric consumption and ratings of hunger and satiety.

METHODS

During the ad libitum portion of a 16 weeks research high-protein feeding study, 19 participants were allowed to eat up to one self-selected meal (SSM) a week instead of an intervention diet meal. The SSM was assessed for total caloric and macronutrient composition and compared to the intervention diet for 3 days before and after the SSM day. Visual analog scores rating daily hunger and fullness were collected and compared as well.

RESULTS

On the SSM day, the mean ± SD daily caloric intake increased by 262 ± 332 kcal compared to the previous study days (P < 0.001), with no changes in subjective appetite scores. The following day there was a slight but significant reduction in intake (- 58 ± 85 kcal, P = 0.008) compared to the average pre-SSM day with no change in appetite scores. On the SSM day, percent protein intake was inversely associated mean daily caloric intake (r² = 0.22, P = 0.03).

CONCLUSIONS

During a long-term, ad-libitum high-protein feeding study, one SSM lower in protein increased daily total caloric consumption with no impact on appetite ratings and incomplete caloric consumption during subsequent days. These data suggest that during ad-libitum feeding, a single meal change in protein content impacts the relationships between daily level of hunger, satiety and calorie intake.

CLINICALTRIALS

GOV ID

NCT05002491 (retrospectively registered 07/20/2021).

Case Report: Thrombotic-Thrombocytopenic Purpura Following Ipilimumab and Nivolumab Combination Immunotherapy for Metastatic Melanoma

A man in his early 50s presented with small bowel obstruction, requiring emergency laparoscopic small bowel resection for the metastatic melanoma of the jejunum with no identifiable primary lesion. One week after his first treatment with ipilimumab and nivolumab, he presented with diffuse abdominal pain, constipation, and fatigue. A computerized tomography scan did not identify a cause for his symptoms. This was rapidly followed by thrombocytopenia on day 11 and then anemia. He commenced intravenous corticosteroids for a suspected diagnosis of immune-related thrombocytopenia. On day 15, a generalized onset motor seizure occurred, and despite plasmapheresis later that day, the patient died from fatal immune-related thrombotic thrombocytopenic purpura (TTP). This was confirmed with suppressed ADAMTS13 (<5%) testing on day 14. Immune-related TTP is a rare and, in this case, fatal immune- related adverse event. Further studies are required to identify additional immunosuppressive management for immune-related TTP.

Adjuvant sunitinib following chemoradiotherapy and surgery for locally advanced esophageal cancer: a phase II trial

The prognosis for locally advanced esophageal cancer is poor despite the use of trimodality therapy. In this phase II study, we report the feasibility, tolerability and efficacy of adjuvant sunitinib. Included were patients with stage IIa, IIB or III cancer of the thoracic esophagus or gastroesophageal junction. Neoadjuvant therapy involved Irinotecan (65 mg/m² ) + Cisplatin (30 mg/m² ) on weeks 1 and 2, 4 and 5, 7 and 8 with concurrent radiation (50Gy/25 fractions) on weeks 4-8. Sunitinib was commenced 4-13 weeks after surgery and continued for one year. Sixty-one patients were included in the final analysis, 36 patients commenced adjuvant sunitinib. Fourteen patients discontinued sunitinib due to disease recurrence (39%) within the 12-month period, 12 (33%) discontinued due to toxicity, and 3 (8%) requested cessation of therapy. In the overall population, median survival was 26 months with a 2 and 3-year survival rate of 52% and 35%, respectively. The median survival for the 36 patients treated with sunitinib was 35 months and 2-year survival probability of 68%. In a historical control, a prior phase II study with the same trimodality therapy (n = 43), median survival was 36 months, with a 2-year survival of 67%. Initiation of adjuvant sunitinib is feasible, but poorly tolerated, with no signal of additional benefit over trimodality therapy for locally advanced esophageal cancer.

Degree of tumor shrinkage following neoadjuvant chemoradiotherapy: a potential predictor for complete pathological response in esophageal cancer?

Neoadjuvant chemoradiotherapy (CRT) before surgery results in a pathological complete response (pCR) rate in about 1/3 of the patients, which is correlated with survival. It was hypothesized that volumetric tumor response to CRT would correlate with outcomes. Patients who completed trimodality therapy, where planning, pre-, and post-CRT computed tomography scans were available, and pathology was reviewed by a central pathologist, were eligible for analysis. Absolute and relative tumor volume change pretreatment and post-treatment were correlated with pCR, locoregional recurrence (LRR), disease-free survival, and overall survival. Fifty-six patients were analyzed. pCR was observed in 30% of patients. Median follow up was 20.3 (range 4-89) months. The 2- and 4-year overall survival was 61.3% (95% confidence interval [CI]: 45-74) and 25.0% (95%CI: 11-41); proportion disease free was 32.1% (95% CI: 19-46) and 20.6% (9-36) at 2 and 4 years, respectively. The median relative volume reduction was 17% (95% CI: -24, -3%). Using 20% as the criteria, the proportion of patients with pCR of ≥20% versus <20% was 13/25 (52%) versus 4/31 (13%) for those who did not (odds ratio 7.3; 95% CI: 2-27). The LRR at 2 and 4 years were 29.5% (95% CI: 16-43) and 36.2% (95% CI: 23-50). The relative tumor reduction ≥20% was significantly correlated with LRR (hazard ratio 0.24; 95% CI: 0.07-0.8; p 0.02) at 2 and 4 years, respectively. Relative tumor volume reduction following CRT is correlated with pCR and LRR. Further investigations are warranted to examine the effect of volume change, alone or in conjunction with other factors as potential predictors for pathological response.

Neutrophil/lymphocyte ratio as a prognostic factor in biliary tract cancer

BACKGROUND

Biliary tract cancers (BTCs) include intrahepatic (IHC), hilar, distal bile duct (DBD) and gallbladder carcinoma (GBC). Neutrophil/lymphocyte ratio (NLR), a marker of host inflammation, is prognostic in several cancers but has not been reviewed in large BTC series, or advanced BTC (ABTC) at diagnosis.

PATIENTS AND METHODS

Baseline demographics and NLR at diagnosis were retrospectively evaluated in 864 consecutive patients with BTC treated from January 1987 to December 2012. The association between NLR and overall survival (OS) was determined using a multivariable Cox proportional hazards model.

RESULTS

Eight hundred and sixty-four patients were included in the analysis, of which 62% had ABTC and 38% had surgery with curative intent. Median age was 65 years, 444 (51%) were male and 727 (84%) had performance status (PS) ⩽ 2. A NLR ⩾ 3.0, PS >2, IHC primary, stage, lack of surgery, haemoglobin <110 g/L and albumin <40 g/L were associated with significantly worse OS on multivariable analysis. A NLR ⩾ 3.0 was an independent prognostic factor for OS for the entire cohort; median OS was 21.6 months versus 12.0 months for patients with NLR <3.0 versus NLR ⩾ 3.0 respectively (adjusted hazard ratio (HR)-1.26, 95% confidence interval (CI); 1.06-1.50, P = 0.01). NLR was also prognostic in patients with ABTC (HR-1.26, 95% CI; 1.02-1.56, P = 0.035) and hilar cancer: overall group (N = 149) (HR-1.70, 95% CI; 1.10-2.50, P = 0.01) and advanced group (N = 111) (HR-1.57, 95% CI; 1.04-2.44, P = 0.048).

CONCLUSION

Baseline NLR is a readily available and inexpensive prognostic biomarker in patients with BTC and likely warrants validation in large prospective clinical trials.

Effects of a high-protein diet on regulation of phosphorus homeostasis

CONTEXT

High-protein diets, which are popular for weight loss, contain large quantities of phosphorus. Phosphorus excess and consequent changes in phosphorus regulatory hormones are implicated in vascular calcification and cardiovascular disease.

OBJECTIVE

We tested the hypothesis that a moderate increase in dietary phosphorus during a high-protein diet leads to changes in phosphorus-responsive hormones.

DESIGN, PARTICIPANTS, AND SETTING

We conducted a post hoc analysis of a sequential dietary modification trial in 19 healthy volunteers in the general community.

INTERVENTION

Participants received 2 weeks of a weight-maintaining, low-protein (15%) diet, followed by 2 weeks of an isocaloric, high-protein (30%) diet, followed by 12 weeks of an ad libitum high-protein (30%) diet.

MAIN OUTCOME MEASURES

Using previously collected samples, plasma concentrations of fibroblast growth factor-23 (FGF-23), PTH, 1,25-dihydroxyvitamin D, and 24,25-dihydroxyvitamin D were measured at 8 time points to assess 24-hour variability and in 24-hour pooled samples to delineate changes at the end of each diet period.

RESULTS

Mean dietary phosphorus intake during each study period was 1556, 2071, and 1622 mg/d, respectively. Plasma concentrations of FGF-23 and vitamin D metabolites varied in a diurnal pattern; plasma PTH concentrations varied in a bimodal pattern. After changing from a low- to high-protein isocaloric diet, plasma FGF-23 concentrations decreased slightly (mean -4.48 pg/mL, 95% confidence interval 1.88-7.07). There were no other statistically significant changes in phosphorus regulatory hormones in response to diet modifications.

CONCLUSIONS

Among healthy people, an approximate 33% increase in dietary phosphorus after institution of a high-protein diet does not cause large changes in measured concentrations of phosphorus regulatory hormones.

Rapid duplex immunoassay for wound biomarkers at the point-of-care

In this study we describe a novel method of sampling and quantifying wound biomarkers for clinical settings. We believe the chosen format will allow rapid assessments of wound healing and provide biomarker evidence-based decision points for treatment of the wound at the time of presentation. The wound monitoring principle uses a proprietary sample collection tool (a thermally reversible hydrogel) to sample and isolate biomarkers within a wound environment without further sample extraction/preparation steps. We show how gel samples can be analysed in a lateral flow assay format utilising fluorescent microspheres with optically discrete emission characteristics and demonstrate quantitative detection of two analytes (duplexing) achieved in a single test line. As a model assay, the chronic wound biomarkers interleukin 6 (IL6) and tumour necrosis factor alpha (TNFα) are used. Limits of detection of 48.5 pg/mL and 55.5 pg/mL respectively in hydrogel samples and 7.15 pg/mL and 10.7 pg/mL respectively in plasma are reported. We believe this is the first literature example of quantitative detection of multiple analytes within a single test line using spectral separation to distinguish the analytes.

Capecitabine or infusional 5-fluorouracil for gastroesophageal cancer: a cost-consequence analysis

BACKGROUND

In patients with advanced gastroesophageal cancer, the phase iii Randomized ECF for Advanced and Locally Advanced Esophagogastric Cancer 2 (real-2) trial demonstrated equivalent clinical efficacy when capecitabine (x) was substituted for 5-fluorouracil (5fu) in the epirubicin-cisplatin-5fu (ecf) regimen. The present analysis compares the direct medical costs associated with both regimens.

METHODS

This cost-consequence analysis of direct medical costs took resource utilization data from the real-2 trial where available. Direct medical costs were derived from the perspective of the Canadian public health care system in 2008 Canadian dollars. Mean cost per patient on each treatment arm was calculated.

RESULTS

Drug costs from start of treatment until first progression, including pre- and post-chemotherapy medications and administration costs, totalled $5,344 for ecx as compared with $3,187 for ecf. Costs for treatment of adverse events were estimated at $2,621 for ecx as compared with $3,397 for ecf. An additional cost of $873 was associated with insertion of an implanted venous access. Total incremental cost of ecx over ecf was $508.

CONCLUSIONS

In advanced gastroesophageal cancer, capecitabine is an attractive alternative to 5fu. Although the drug cost per se is greater, use of capecitabine is associated with decreased consumption of hospital resources. Not only does capecitabine fit with patient preference for oral therapy, it also avoids the inconvenience and complications of central venous access.

The requirement of Ras and Rap1 for the activation of ERKs by cAMP, PACAP, and KCl in cerebellar granule cells

In cerebellar granule cells, the mitogen-activated protein kinase (MAPK) or extracellular signal-regulated kinase (ERK) cascade mediates multiple functions, including proliferation, differentiation, and survival. In these cells, ERKs are activated by diverse stimuli, including cyclic adenosine monophosphate (cAMP), pituitary adenylate cyclase activating protein (PACAP), depolarization induced by elevated extracellular potassium (KCl), and the neurotrophin brain-derived neurotrophic factor. Extensive studies in neuronal cell lines have implicated the small G proteins Ras and Rap1 in the activation of ERKs by cAMP, PACAP, and KCl. However, the requirement of Ras and Rap1 in these pathways in cerebellar granule cells has not been addressed. In this study, we utilize multiple biochemical assays to determine the mechanisms of action and requirement of Ras and Rap1 in cultured cerebellar granule cells. We show that both Ras and Rap1 can be activated by cAMP or PACAP via protein kinase (PKA)-dependent mechanisms. KCl activation of Ras also required PKA. Using both adenoviral and transgenic approaches, we show that Ras plays a major role in ERK activation by cAMP, PACAP, and KCl, while Rap1 also mediates activation of a selective membrane-associated pool of ERKs. Furthermore, Rap1, but not Ras, activation by PKA appears to require the action of Src family kinases.

Taxane-resistant lymphoepithelial-like carcinoma: Excellent response to VIP chemotherapy

BACKGROUND

Lymphoepithelial-like carcinoma is a rare tumour type. The optimal treatment for this disease is not known. No effective therapies are described in the literature.

AIMS

This report describes a case of lymphoepithelial-like carcinoma and documents a therapeutic strategy which has proved effective.

RESULTS

The patient was initially treated with a common platinum-based chemotherapy regimen incorporating a taxane (Carbplatin and Docetaxel). Disease stabilization initially occurred but the patient soon progressed. The patient was then treated with VIP chemotherapy and had a complete response.

CONCLUSION

VIP chemotherapy appears to be an effective therapeutic strategy in lymphoepithelial-like carcinoma.

Examining the mechanism of Erk nuclear translocation using green fluorescent protein

In neuronal cells, the mitogen-activated protein kinase (MAP kinase) cascade is an important mediator of neurotrophin signaling from cell surface receptors to the nucleus, resulting in changes in gene expression. Nuclear localization of Erk is thought to be required for these effects. To examine the mechanism and regulation of Erk nuclear translocation, we have created a green fluorescent protein (GFP)-labeled Erk2 construct, which provides a sensitive means to follow the movement of Erk from the cytoplasm to the nucleus following receptor-mediated MAP kinase activation. Using this system in PC12 cells, we have examined a number of mechanisms that have been implicated in regulating the translocation of Erk. In PC12 cells, NGF and EGF induce a rapid translocation of GFP-Erk that requires Ras and Mek. We have found that prolonged phosphorylation of Erk is not required for the rapid and early influx of Erk into the nucleus following growth factor stimulation. Furthermore, following influx, GFP-Erk rapidly returned to the cytoplasm regardless of its phosphorylation state. The release of Erk from its cytoplasmic activator, Mek, followed by the dimerization of Erk, was sufficient to stimulate nuclear uptake, whereas Erk kinase activity was dispensable. PKA activity has been reported to be required for Erk translocation in PC12 cells. However, PKA activity was also not necessary for the early translocation of Erk into the nucleus by NGF or Ras, but it was able to induce a small influx of Erk that could be measured with GFP-Erk2.

Neuronal calcium activates a Rap1 and B-Raf signaling pathway via the cyclic adenosine monophosphate-dependent protein kinase

Activity-dependent regulation of neuronal events such as cell survival and synaptic plasticity is controlled by increases in neuronal calcium levels. These actions often involve stimulation of intracellular kinase signaling pathways. For example, the mitogen-activated protein kinase, or extracellular signal-regulated kinase (ERK), signaling cascade has increasingly been shown to be important for the induction of gene expression and long term potentiation. However, the mechanisms leading to ERK activation by neuronal calcium are still unclear. In the present study, we describe a protein kinase A (PKA)-dependent signaling pathway that may link neuronal calcium influx to ERKs via the small G-protein, Rap1, and the neuronal Raf isoform, B-Raf. Thus, in PC12 cells, depolarization-mediated calcium influx led to the activation of B-Raf, but not Raf-1, via PKA. Furthermore, depolarization also induced the PKA-dependent stimulation of Rap1 and led to the formation of a Rap1/B-Raf signaling complex. In contrast, depolarization did not lead to the association of Ras with B-Raf. The major action of PKA-dependent Rap1/B-Raf signaling in neuronal cells is the activation of ERKs. Thus, we further show that, in both PC12 cells and hippocampal neurons, depolarization-induced calcium influx stimulates ERK activity in a PKA-dependent manner. Given the fact that both Rap1 and B-Raf are highly expressed in the central nervous system, we suggest that this signaling pathway may regulate a number of activity-dependent neuronal functions.

G protein-mediated inhibition of neuronal migration requires calcium influx

Neuronal migration is an essential feature of the developing nervous system, but the intracellular signaling mechanisms that regulate this process are poorly understood. During the formation of the enteric nervous system (ENS) in the moth Manduca sexta, the migration of an identified set of neurons (the EP cells) is regulated in part by the heterotrimeric guanyl-nucleotide binding protein (G protein) Goalpha. Using an in vivo culture preparation for developing embryos that allows direct access to the ENS, we have shown that EP cell migration is similarly regulated by intracellular Ca2+; treatments that increased intracellular Ca2+ inhibited the migratory process, whereas buffering intracellular Ca2+ induced aberrant migration onto inappropriate pathways. Imaging the spontaneous changes in intracellular Ca2+ within individual EP cells showed that actively migrating neurons exhibited only small fluctuations in intracellular Ca2+. In contrast, neurons that had reached the end of migration displayed large, transient Ca2+ spikes. Similar Ca2+ spikes were induced in the EP cells by G protein stimulation, an effect that was reversed by removal of external Ca2+. Stimulation of Go in individual EP cells (by injection of either activated Goalpha subunits or mastoparan) also inhibited migration in a Ca2+-dependent manner. These results suggest that the regulation of neuronal migration by G proteins involves a Ca2+-dependent process requiring Ca2+ influx.

An identified set of visceral muscle bands is essential for the guidance of migratory neurons in the enteric nervous system of Manduca sexta

During the formation of the enteric nervous system (ENS) in Manduca, a population of approximately 300 enteric neurons (the EP cells) become distributed along the foregut and midgut by migrating onto specific sets of visceral muscle bands. Only after their migration is complete do the neurons express a variety of position-specific phenotypes, including a peptidergic phenotype that is usually restricted to a subset of EP cells on the midgut. To investigate whether direct interactions between the EP cells and these pathways are necessary for either neuronal migration or differentiation, we have investigated the developmental origins and functional role of the muscle bands in embryonic culture. Using scanning electron microscopy, immunohistochemistry, and mitotic labeling with bromodeoxyuridine, we found that the eight major muscle bands of the midgut form by the coalescence of longitudinal muscle fibers on the midgut surface, apparently in response to regional cues associated with the underlying epithelium. These bands then serve as migratory pathways for the EP cells, which travel rapidly along the bands (but not onto adjacent interband musculature) and then complete their differentiation. Dye labeling of individual EP cells revealed that prior to migration onset, each neuron extended widely distributed filopodia onto both the band and interband regions of the midgut surface. As the muscle bands coalesced, however, the leading process of each EP cell became increasingly confined to a specific band, onto which it subsequently migrated. In a series of surgical manipulations of both the muscle bands and the migratory neurons, we demonstrated that these pathways are both necessary and sufficient to support the migratory behavior of the EP cells. Surgical interventions that prevented the neurons from contacting the muscle bands inhibited migration, while contact between isolated EP cells and a muscle band supported both their migration and differentiation. However, the acquisition of mature phenotypes by the EP cells was not strictly dependent on the migration of these neurons to their expected positions. In particular, the onset of neuropeptide expression could be detected in at least some of the neurons whose migration onto the midgut had been blocked. Thus, in the embryonic ENS, the migration and delayed differentiation of the EP cells represent precisely coordinated aspects of development that are nevertheless regulated in an independent manner.

A developmental role for the heterotrimeric G protein Go alpha in a migratory population of embryonic neurons

The heterotrimeric G proteins are an extended family of guanyl nucleotide-binding proteins that serve essential functions in the mature nervous system but whose contributions to neuronal development remain poorly understood. We have investigated the potential role of one specific G protein, Go(alpha), in the control of neuronal migration. During embryogenesis of the moth, Manduca sexta, an identified population of undifferentiated neurons (the EP cells) migrate along sets of visceral muscle bands to form part of the enteric nervous system. Previously, immunohistochemical studies indicated the presence of Go(alpha)-related proteins in the EP cells during migration. We have now verified this result, using probes derived from the Go(alpha) gene in Manduca. A clone containing the full-length coding domain for Go(alpha) was sequenced from a Manduca cDNA library; digoxigenin-labeled probes were then made from this clone and used to examine the developmental expression of the Go(alpha) gene during embryogenesis. Go(alpha)-specific transcripts could first be detected in the EP cells several hours before the onset of their migration. The level of Go(alpha) expression in all of the EP cells continued to increase during migration, but subsequently was down-regulated in a subset of the postmigratory neurons at the time of their terminal differentiation. This pattern of regulated expression is consistent with the distribution of Go(alpha)-related protein in the EP cells. We also used a semi-intact culture preparation of staged embryos to investigate the effects of G protein-specific toxins on the migratory process. Intracellular injections of the wasp toxin mastoparan, a specific activator of Go(alpha)-and Gi(alpha)-related proteins, inhibited the migration of individual EP cells. Injections of pertussis toxin (an inhibitor of Go(alpha) and Gi(alpha)) or cholera toxin (a selective activator of Gs(alpha)) had no effect on migration, although pertussis toxin treatments did cause a measurable increase in the subsequent outgrowth of axonal processes. However, co-injection of mastoparan with pertussis toxin blocked the inhibitory effects of mastoparan alone. These results suggest that Go(alpha)-coupled signaling events within the EP cells may down-regulate their migratory behavior, possibly in response to inhibitory cues that normally guide migration in the developing embryo.

Developmental expression of heterotrimeric G proteins in the nervous system of Manduca sexta

The heterotrimeric G proteins are a conserved family of guanyl nucleotide-binding proteins that appear in all eukaryotic cells but whose developmental functions are largely unknown. We have examined the developmental expression of representative G proteins in the developing nervous system of the moth Manduca sexta. Using affinity-purified antisera against different G alpha subunits, we found that each of the G proteins exhibited distinctive patterns of expression within the developing central nervous system (CNS), and that these patterns underwent progressive phases of spatial and temporal regulation that corresponded to specific aspects of neuronal differentiation. Several of the G proteins examined (including Gs alpha and G(o) alpha) were expressed in an apparently ubiquitous manner in all neurons, but other proteins (including Gi alpha) were ultimately confined to a more restricted subset of cells in the mature CNS. Although most of the G proteins examined could be detected within the central ganglia, only G(o) alpha-related proteins were seen in the developing peripheral nerves; manipulations of G protein activity in cultured embryos suggested that this class of G protein may contribute to the regulation of neuronal motility during axonal outgrowth. G(o) alpha-related proteins were also localized to the developing axons and terminals of the developing adult limb during metamorphosis. These intracellular signaling molecules may, therefore, play similar developmental roles in both the embryonic and postembryonic nervous system.

Developmental expression of G proteins in a migratory population of embryonic neurons

Directed neuronal migration contributes to the formation of many developing systems, but the molecular mechanisms that control the migratory process are still poorly understood. We have examined the role of heterotrimeric G proteins (guanyl nucleotide binding proteins) in regulating the migratory behavior of embryonic neurons in the enteric nervous system of the moth, Manduca sexta. During the formation of the enteric nervous system, a group of approx. 300 enteric neurons (the EP cells) participate in a precise migratory sequence, during which the undifferentiated cells populate a branching nerve plexus that lies superficially on the visceral musculature. Once migration is complete, the cells then acquire a variety of position-specific neuronal phenotypes. Using affinity-purified antisera against different G protein subtypes, we found no apparent staining for any G protein in the EP cells prior to their migration. Coincident with the onset of migration, however, the EP cells commenced the expression of one particular G protein, Go alpha. The intensity of immunostaining continued to increase as migration progressed, with Go alpha immunoreactivity being detectable in the leading processes of the neurons as well as their somata. The identity of the Go alpha-related proteins was confirmed by protein immunoblot analysis and by comparison with previously described forms of Go alpha from Drosophila. When cultured embryos were treated briefly with aluminium fluoride, a compound known to stimulate the activity of heterotrimeric G proteins, both EP cell migration and process outgrowth were inhibited. The effects of aluminium fluoride were potentiated by alpha toxin, a pore-forming compound that by itself caused no significant perturbations of migration. In preliminary experiments, intracellular injections of the non-hydrolyzable nucleotide GTP gamma-S also inhibited the migration of individual EP cells, supporting the hypothesis that G proteins play a key role in the control of neuronal motility in this system. In addition, once migration was complete, the expression of Go alpha-related proteins in the EP cells underwent a subsequent phase of regulation, so that only certain phenotypic classes among the differentiated EP cells retained detectable levels of Go alpha immunoreactivity. Thus Go may perform multiple functions within the same population of migratory neurons in the course of embryonic development.