Correction: Haegeman et al. Looking beyond Virus Detection in RNA Sequencing Data: Lessons Learned from a Community-Based Effort to Detect Cellular Plant Pathogens and Pests. Plants 2023, 12, 2139.

In the original publication [...].

Looking beyond Virus Detection in RNA Sequencing Data: Lessons Learned from a Community-Based Effort to Detect Cellular Plant Pathogens and Pests.

High-throughput sequencing (HTS), more specifically RNA sequencing of plant tissues, has become an indispensable tool for plant virologists to detect and identify plant viruses. During the data analysis step, plant virologists typically compare the obtained sequences to reference virus databases. In this way, they are neglecting sequences without homologies to viruses, which usually represent the majority of sequencing reads. We hypothesized that traces of other pathogens might be detected in this unused sequence data. In the present study, our goal was to investigate whether total RNA-seq data, as generated for plant virus detection, is also suitable for the detection of other plant pathogens and pests. As proof of concept, we first analyzed RNA-seq datasets of plant materials with confirmed infections by cellular pathogens in order to check whether these non-viral pathogens could be easily detected in the data. Next, we set up a community effort to re-analyze existing Illumina RNA-seq datasets used for virus detection to check for the potential presence of non-viral pathogens or pests. In total, 101 datasets from 15 participants derived from 51 different plant species were re-analyzed, of which 37 were selected for subsequent in-depth analyses. In 29 of the 37 selected samples (78%), we found convincing traces of non-viral plant pathogens or pests. The organisms most frequently detected in this way were fungi (15/37 datasets), followed by insects (13/37) and mites (9/37). The presence of some of the detected pathogens was confirmed by independent (q)PCRs analyses. After communicating the results, 6 out of the 15 participants indicated that they were unaware of the possible presence of these pathogens in their sample(s). All participants indicated that they would broaden the scope of their bioinformatic analyses in future studies and thus check for the presence of non-viral pathogens. In conclusion, we show that it is possible to detect non-viral pathogens or pests from total RNA-seq datasets, in this case primarily fungi, insects, and mites. With this study, we hope to raise awareness among plant virologists that their data might be useful for fellow plant pathologists in other disciplines (mycology, entomology, bacteriology) as well.

Identification of Volatile Organic Compounds Produced by Xenorhabdus indica Strain AB and Investigation of Their Antifungal Activities.

Xenorhabdus spp. are symbiotic bacteria associated with entomopathogenic nematodes to form a model complex that is used for the biological control of insect pests. These bacteria also produce secondary metabolites that have commercial potential in the pharmaceutical and agroforestry industries. Volatile organic compounds (VOCs) produced by the Xenorhabdus indica "strain AB" have been shown to have significant antifungal activity against Fusarium oxysporum f. sp. cucumerinum. Using gas chromatography-mass spectrometry, we identified 61 volatiles in the mixture of VOCs emitted by strain AB compared to a control strain, 6 of which were investigated for their antifungal activities. Of these, methyl anthranilate exhibited the highest mycelial growth suppression toward F. oxysporum, with a minimum inhibitory volume (MIV) of 50 µL/plate. Fluorescence assays, scanning electron microscopy, and measurements of the leakage of intracellular components revealed that the use of methyl anthranilate changed cell wall and cell membrane integrity as well as the permeability of the plasma membrane. Furthermore, methyl anthranilate treatment upregulated the transcription level of target genes related to redox reactions and the cell wall integrity pathway. The results suggest a novel mechanism used by Xenorhabdus spp. to overcome competitors during its life cycle and open up a new approach to using these bacteria in biological control. IMPORTANCE Fungal phytopathogens, particularly Fusarium oxysporum, are a major problem worldwide, especially in the postharvest of vital economic crops. Concerns about negative effects on the environment and human health have led to increasing restrictions on the use of chemical fungicides, and therefore, biological control agents are now being considered alternatives. It is in this context that we investigated the antifungal activity of VOCs produced by X. indica strain AB against F. oxysporum. We found that AB VOCs have a strong effect on the growth of the fungal phytopathogen. In addition, 85% of the identified volatile compounds were determined to be new compounds, opening up new lines of research to discover their properties, effects, and potential for pharmaceutical and agricultural applications. Antifungal assays proved that four of the six compounds with a high concentration in the GC-MS profile had a significant inhibitory effect on pathogen growth. Accordingly, this study opens up a new approach for the use of these bacteria in biocontrol.

Biological and Genetic Characterization of Physostegia Chlorotic Mottle Virus in Europe Based on Host Range, Location, and Time.

Application of high throughput sequencing (HTS) technologies enabled the first identification of Physostegia chlorotic mottle virus (PhCMoV) in 2018 in Austria. Subsequently, PhCMoV was detected in Germany and Serbia on tomatoes showing severe fruit mottling and ripening anomalies. We report here how prepublication data-sharing resulted in an international collaboration across eight laboratories in five countries, enabling an in-depth characterization of PhCMoV. The independent studies converged toward its recent identification in eight additional European countries and confirmed its presence in samples collected 20 years ago (2002). The natural plant host range was expanded from two to nine species across seven families, and we confirmed the association of PhCMoV presence with severe fruit symptoms on economically important crops such as tomato, eggplant, and cucumber. Mechanical inoculations of selected isolates in the greenhouse established the causality of the symptoms on a new indexing host range. In addition, phylogenetic analysis showed a low genomic variation across the 29 near-complete genome sequences available. Furthermore, a strong selection pressure within a specific ecosystem was suggested by nearly identical sequences recovered from different host plants through time. Overall, this study describes the European distribution of PhCMoV on multiple plant hosts, including economically important crops on which the virus can cause severe fruit symptoms. This work demonstrates how to efficiently improve knowledge on an emergent pathogen by sharing HTS data and provides a solid knowledge foundation for further studies on plant rhabdoviruses.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Interlaboratory Comparison Study on Ribodepleted Total RNA High-Throughput Sequencing for Plant Virus Diagnostics and Bioinformatic Competence.

High-throughput sequencing (HTS) technologies and bioinformatic analyses are of growing interest to be used as a routine diagnostic tool in the field of plant viruses. The reliability of HTS workflows from sample preparation to data analysis and results interpretation for plant virus detection and identification must be evaluated (verified and validated) to approve this tool for diagnostics. Many different extraction methods, library preparation protocols, and sequence and bioinformatic pipelines are available for virus sequence detection. To assess the performance of plant virology diagnostic laboratories in using the HTS of ribosomal RNA depleted total RNA (ribodepleted totRNA) as a diagnostic tool, we carried out an interlaboratory comparison study in which eight participants were required to use the same samples, (RNA) extraction kit, ribosomal RNA depletion kit, and commercial sequencing provider, but also their own bioinformatics pipeline, for analysis. The accuracy of virus detection ranged from 65% to 100%. The false-positive detection rate was very low and was related to the misinterpretation of results as well as to possible cross-contaminations in the lab or sequencing provider. The bioinformatic pipeline used by each laboratory influenced the correct detection of the viruses of this study. The main difficulty was the detection of a novel virus as its sequence was not available in a publicly accessible database at the time. The raw data were reanalysed using Virtool to assess its ability for virus detection. All virus sequences were detected using Virtool in the different pools. This study revealed that the ribodepletion target enrichment for sample preparation is a reliable approach for the detection of plant viruses with different genomes. A significant level of virology expertise is needed to correctly interpret the results. It is also important to improve and complete the reference data.

Molecular characterisation of a new tenuivirus from Festuca sp.

A novel virus with a quadruple genome of negative-sense, single-stranded RNA was identified by high-throughput sequencing (HTS) in a grass sample from Saxony-Anhalt, Germany, and tentatively called Festuca stripe-associated virus (FSaV). The genome of FSaV consists of four segments and a total of 16,535 nucleotides (nt) which encode seven open reading frames (ORF). FSaV shares highest nt identity (between 72.84% to 80.74%) to Iranian wheat stripe virus (IWSV) and rice hoja blanca virus (RHBV). Additionally, pairwise comparisons between the amino acid sequences of the ORFs on the genome of FSaV and the corresponding ones on the genomes of the members of the Tenuvirus genus showed that FSaV shared 83.17% and 90.85% (amino acid) aa identity to IWSV. Moreover, the non-coding intergenic regions (ncIR) shared only between 49.5% to 60.87% nt identity to the corresponding regions on the IWSV genome. Based on the ICTV species demarcation, the results suggest that FSaV may represent a new species of the genus Tenuivirus. Plastid sequence analysis of the HTS data showed that the original host is a member of the genus Festuca most likely the species Festuca pratensis.

Investigating the Pea Virome in Germany-Old Friends and New Players in the Field(s).

Peas are an important legume for human and animal consumption and are also being used as green manure or intermediate crops to sustain and improve soil condition. Pea production faces constraints from fungal, bacterial, and viral diseases. We investigated the virome of German pea crops over the course of three successive seasons in different regions of pea production to gain an overview of the existing viruses. Pools from 540 plants, randomly selected from symptomatic and asymptomatic peas, and non-crop plants surrounding the pea fields were used for ribosomal RNA-depleted total RNA extraction followed by high-throughput sequencing (HTS) and RT-PCR confirmation. Thirty-five different viruses were detected in addition to nine associated nucleic acids. From these viruses, 25 are classified as either new viruses, novel strains or viruses that have not been reported previously from Germany. Pea enation mosaic virus 1 and 2 were the most prevalent viruses detected in the pea crops, followed by pea necrotic yellow dwarf virus (PNYDV) and turnip yellows virus which was also found also in the surrounding non-legume weeds. Moreover, a new emaravirus was detected in symptomatic peas in one region for two successive seasons. Most of the identified viruses are known to be aphid transmissible. The results revealed a high virodiversity in the German pea fields that poses new challenges to diagnosticians, researchers, risk assessors and policy makers, as the impact of the new findings are currently unknown.

Complete Genome Sequence of a Soybean Dwarf Virus Isolate from White Clover in Germany.

In this study, we present the complete genome of a new isolate of soybean dwarf virus (SbDV) (genus Luteovirus, family Luteoviridae) from white clover in Germany. The complete genome of the isolate (JKI ID 23556) consists of 5,858 nucleotides and displays 94.98% nucleotide identity to its most similar SbDV relative (GenBank accession number MN412736).

Aphid transmission of nanoviruses.

The genus Nanovirus consists of plant viruses that predominantly infect legumes leading to devastating crop losses. Nanoviruses are transmitted by various aphid species. The transmission occurs in a circulative nonpropagative manner. It was long suspected that a virus-encoded helper factor would be needed for successful transmission by aphids. Recently, a helper factor was identified as the nanovirus-encoded nuclear shuttle protein (NSP). The mode of action of NSP is currently unknown in contrast to helper factors from other plant viruses that, for example, facilitate binding of virus particles to receptors within the aphids' stylets. In this review, we are summarizing the current knowledge about nanovirus-aphid vector interactions.

Chlorhexidine-alcohol versus povidone-iodine for skin preparation before elective cesarean section: a prospective observational study.

Introduction: The ideal antiseptic agent for skin preparation before elective cesarean section (CS) is not yet determined. The aim of the study was to assess the impact of skin preparation by chlorhexidine-alcohol compared with povidone-iodine before elective CS on the rate of surgical site infection (SSI).Materials and methods: This prospective observational study included a total of 1424 pregnant women at term who were candidates for the elective CS and were divided into two equal groups of 712 patients in each, group 1 (chlorhexidine-alcohol group) and group 2 (povidone-iodine group). Patients were followed up at 1 week and 1 month postoperative to determine the rate of SSI.Results: The rate of SSI was 3.7% (26 patients) in the chlorhexidine-alcohol group compared with 4.6% (33 patients) in the povidone-iodine group (odds ratio: 0.7798, 95% CI: 0.46-1.3, p = .35), nine patients in the chlorhexidine-alcohol group, and 10 patients in the povidone-iodine group required resuturing (odds ratio: 0.9, 95% CI: 0.36-2.2, p = .82). Four patients (0.56%) in the chlorhexidine-alcohol group and five patients (0.7%) in the povidone-iodine group developed endometritis (p = .74). The rate or readmission because of SSI was 2.7% (19 patients) in the chlorhexidine-alcohol group and 2.9% (21 patients) in the povidone-iodine group (p = .75).Conclusions: Skin preparation with either chlorhexidine-alcohol or povidone-iodine resulted in comparable rates of SSIs. Accordingly, both are suitable antiseptic agents for skin preparation before elective CS.

A divergent strain of melon chlorotic spot virus isolated from black medic (Medicago lupulina) in Austria.

A tenuivirus, referred to here as JKI 29327, was isolated from a black medic (Medicago lupulina) plant collected in Austria. The virus was mechanically transmitted to Nicotiana benthamiana, M. lupulina, M. sativa, Pisum sativum and Vicia faba. The complete genome was determined by high throughput sequencing. The genome of JKI 29327 consists of eight RNA segments closely related to those of melon chlorotic spot virus (MeCSV) isolate E11-018 from France. Since segments RNA 7 and 8 of JKI 29327 are shorter, its genome is slightly smaller (by 247 nts) than that of E11-018. Pairwise comparisons between the predicted virus proteins of JKI 29327 and their homologues in E11-018 showed aa identities ranging from 80.6 to 97.2%. Plants infected with E11-081 gave intermediate DAS-ELISA reactions with polyclonal antibodies to JKI 29327. Since JKI 29327 and E11-018 appear to be closely related both serologically and genetically, we propose to regard JKI 29327 as the black medic strain of MeCSV. To our knowledge, JKI 29327 represents the second tenuivirus identified from a dicotyledonous plant. Serological and molecular diagnostic methods were developed for future detection.

Characterisation of a novel nucleorhabdovirus infecting alfalfa (Medicago sativa).

BACKGROUND: Nucleorhabdoviruses possess bacilliform particles which contain a single-stranded negative-sense RNA genome. They replicate and mature in the nucleus of infected cells. Together with viruses of three other genera of the family Rhabdoviridae, they are known to infect plants and can be transmitted by arthropod vectors, during vegetative propagation, or by mechanical means. In 2010, an alfalfa (Medicago sativa) plant showing virus-like symptoms was collected from Stadl-Paura, Austria and sent to Julius Kühn Institute for analysis. METHODS: Electron microscopy (EM) of leaf extracts from infected plants revealed the presence of rhabdovirus-like particles and was further used for ultrastructural analyses of infected plant tissue. Partially-purified preparations of rhabdovirus nucleocapsids were used for raising an antiserum. To determine the virus genome sequence, high throughput sequencing (HTS) was performed. RT-PCR primers were designed to confirm virus infection and to be used as a diagnostic tool. RESULTS: EM revealed bacilliform virions resembling those of plant-infecting rhabdoviruses. HTS of ribosomal RNA-depleted total RNA extracts revealed a consensus sequence consisting of 13,875 nucleotides (nt) and containing seven open reading frames (ORFs). Homology and phylogenetic analyses suggest that this virus isolate represents a new species of the genus Nucleorhabdovirus (family Rhabdoviridae). Since the virus originated from an alfalfa plant in Austria, the name alfalfa-associated nucleorhabdovirus (AaNV) is proposed. Viroplasms (Vp) and budding virions were observed in the nuclei of infected cells by EM, thus confirming its taxonomic assignment based on sequence data. CONCLUSIONS: In this study, we identified and characterised a new nucleorhabdovirus from alfalfa. It shared only 39.8% nucleotide sequence identity with its closest known relative, black currant-associated rhabdovirus 1. The virus contains an additional open reading frame (accessory gene) with unknown function, located between the matrix protein and the glycoprotein genes. Serological and molecular diagnostic assays were designed for future screening of field samples. Further studies are needed to identify other natural hosts and potential vectors.

Complete genome sequence of a highly divergent carrot torradovirus 1 strain from Apium graveolens.

A new virus was identified in a celery plant showing chlorotic rings, mosaic and strong yellowing symptoms, and its complete genome sequence was determined. The genomic organization of this novel virus is analogous to that of known members of the genus Torradovirus, consisting of two single-stranded RNAs of 6,823 (RNA1) and 4,263 nucleotides (RNA2), excluding the poly(A) tails. BLAST searches against the nucleotide and protein databases showed that this virus is closely related to but different from carrot torradovirus 1 (CaTV1). Comparisons between the two viruses demonstrated relatively low levels of nucleotide and amino acid similarity in different parts of their genomes, as well as considerable differences in the sizes of their two genomic RNAs. However, the protease-polymerase (Pro-Pol) and capsid protein (CP) regions of this virus share >80% amino acid identity with the corresponding regions of CaTV1. Therefore, based on the current ICTV species demarcation criteria for the family Secoviridae, the virus from celery is a divergent strain of CaTV1, named "CaTV1-celery". Nevertheless, differences between CaTV1 and CaTV1-celery in genome size, as well as in biological and epidemiological features, may warrant their separation into two distinct species in the future.

Caraway yellows virus, a novel nepovirus from Carum carvi.

A novel nepovirus was identified and characterised from caraway, and tentatively named caraway yellows virus (CawYV). Tubular structures with isomeric virus particles typical for nepoviruses were observed in infected tissues by electron microscopy. The whole genome of CawYV was identified by high throughput sequencing (HTS). It consists of two segments with 8026 nt for RNA1 and 6405 nt for RNA2, excluding the poly(A) tails. CawYV-RNA1 shared closest nt identity to peach rosette mosaic virus (PRMV) with 63%, while RNA2 shared 41.5% with blueberry latent spherical virus (BLSV). The amino acid sequences of the CawYV protease-polymerase (Pro-Pol) and capsid protein (CP) regions share the highest identities with those of the subgroup C nepoviruses. The Pro-Pol region shared highest aa identity with PRMV (80.1%), while the CP region shared 39.6% to soybean latent spherical virus. Phylogenetic analysis of the CawYV-Pro-Pol and -CP aa sequences provided additional evidence of their association with nepoviruses subgroup C. Based on particle morphology, genomic organization and phylogenetic analyses, we propose CawYV as a novel species within the genus Nepovirus subgroup C.

Two Divergent Isolates of Turnip Yellows Virus from Pea and Rapeseed and First Report of Turnip Yellows Virus-Associated RNA in Germany.

Two divergent isolates of turnip yellows virus (TuYV) were identified in pea and rapeseed. The nearly complete genome sequences of the virus isolates share 93.3% nucleotide identity with each other and 89.7% and 92.9% with their closest isolate from South Africa. Additionally, a turnip yellows virus-associated RNA was identified.

Influence of dietary protein, energy and corticosteroids on protein turnover, proteoglycan sulphation and growth of long bone and skeletal muscle in the rat.

1. We report here the extent to which changes in protein turnover contribute to the previously described inhibition of growth of rat tibial length and skeletal muscle mass in response to protein deficiency [1], energy restriction and corticosterone treatment [2]. Measurements of 35S uptake in vivo also enabled the qualitative pattern of changes in proteoglycan synthesis in bone and muscle to be established. 2. Protein deficiency was examined by ad libitum feeding of 20%, 7%, 3.5% and 0.5% protein diets with measurements at 1, 3 and 7 days (all diets), and 14 and 21 days (0.5% protein). In bone this induced delayed inhibition of tibial growth with parallel inhibition of protein synthesis, as measured by the phenylalanine flooding dose method. This was mediated by reductions in both ribosomal capacity (RNA/protein ratio) and activity (protein synthesis/RNA) in the 0.5% protein group. The pattern of inhibition of proteoglycan sulphation, measured as 35S uptake 60 min after injection of a tracer dose of labelled sulphate, was similar to that of protein synthesis. 3. In muscle there was an intermediate graded inhibition of protein synthesis by protein deficiency, mediated by reductions in both ribosomal capacity and activity in the 0.5% protein group, which preceded growth inhibition in the 7% and 3.5% groups, and which was progressive with time. Transient increases in proteolysis contributed to the growth inhibition is some groups, but the rate fell eventually in the 0.5% group. The pattern of response of proteoglycan sulphation differed from protein synthesis with a delayed inhibition, but with subsequent marked reduction. 4. Energy restriction was induced by diets fed for 4 or 8 days at 75%, 50% and 25% ad libitum intakes with protein intakes held constant, and corticosterone treatment involved a dose of 10 mg day-1 100-1 g (subcutaneous) with ad libitum feeding. In bone this induced a pattern of length growth inhibition which was dissociated from inhibition of protein synthesis in the moderately restricted (75% and 50%) groups. Only in the 25% group and in the 8 day corticosterone group was protein synthesis inhibited, through reductions in ribosomal capacity and activity. 35S uptake was also dissociated from growth inhibition, with reduced 35S uptake observed only after corticosterone treatment or 8 days of the 50% or 25% diets. 5. In muscle the energy restriction and corticosterone treatment induced parallel inhibitions of growth and protein synthesis, mediated by similar graded reductions in the RNA/protein ratios and in the 25% group in the KRNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Dietary energy, glucocorticoids and the regulation of long bone and muscle growth in the rat.

1. The influence of dietary energy restriction and corticosterone on long bone and muscle growth, and their interrelationships, was studied in rats fed a range of restricted amounts of diets containing increasing concentrations of protein, thus maintaining constant protein intakes. Tibial length and epiphyseal cartilage width were measured radiographically. 2. In experiment 1, tibial length and gastrocnemius muscle growth were examined in ad libitum fed rats and during 4 days of severe energy restriction (25% ad libitum intake), starvation and ad libitum feeding with corticosterone treatment (10 mg/100 g), a mediator of the response to energy restriction. Weight loss occurred in all groups. Tibial growth continued in the 25% and starvation groups albeit at reduced rates with the inhibition of starvation > 25% group (P < 0.05), but was arrested after 2 days of corticosterone treatment. 3. Muscle growth inhibition was proportional to tibial growth inhibition of the 25% group, insofar as the muscle/bone ratio (W/L), was maintained. This inter-relationship between muscle and bone growth previously reported for ad libitum high-protein-fed rats, is likely to reflect the anabolic influence of bone on muscle via passive muscle stretching induced by length growth. For both starvation and corticosterone groups the muscle/bone ratio fell (P < 0.05 compared with the ad libitum group), suggesting that muscle growth inhibition included an additional direct catabolic influence of starvation and corticosterone treatment. 4. In experiment 2, measurements of bone, muscle and liver growth were made in rats fed 75%, or 50% and 25% ad libitum intakes with corticosterone treatment for 8 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary protein and the regulation of long-bone and muscle growth in the rat.

1. We report here studies of the interrelationship of bone and muscle growth in the rat and the regulatory role of dietary protein. Two experiments were undertaken. In experiment 1, growth inhibition was induced by ad libitum feeding of low protein diets containing 7%, 3.5% or 0.5% protein, with a control group fed a 20% protein diet. Measurements were made at 1, 3 and 7 days. In experiment 2, complete growth inhibition was induced by ad libitum feeding of a 0.5% protein diet with measurements at 7, 14 and 21 days followed by refeeding diets of 3%, 6%, 9%, 12% and 20% protein, with measurements after 3, 7, 10 and 14 days of refeeding (experimental days 24, 28, 31 and 35). Controls fed a 20% protein diet were studied at 0, 14, 21, 24, 28, 31 and 35 days. 2. Body weight growth stopped immediately in all reduced protein groups, with subsequent weight maintenance on the 7% protein diet, slight loss on the 3.5% protein diet or marked weight loss on the 0.5% protein diet, although food intake was maintained for 3 days, falling in all groups after this time. Inhibition of muscle growth was delayed in the 7% and 3.5% protein fed groups, with 12-15% increases in muscle weight after 7 days, but prompt growth inhibition occurred with the 0.5% protein diet with subsequent weight loss. In animals fed the control 20% protein diet, muscle weight (W) reflected tibial length (L) as W = L3.85/10(2.93) (r = 0.98, n = 98). Calculation of the muscle weight/bone length ratio (micrograms/mm3.85) indicated that a significant muscle deficit was apparent on day 3 and subsequently in the 0.5% protein fed rats, but not until day 7 in the 3.5% and 7% protein fed animals. 3. Total tibial length, epiphysis length and epiphyseal cartilage width were measured radiographically. In all groups there was no significant reduction in bone length growth during the first 3 days. After 3 days there were graded reductions on reduced protein intakes with complete inhibition on the 0.5% protein diet. Epiphyseal cartilage width responded sensitively, with a reduction within 24h of the 0.5% and the 3.5% protein diets, and within 3 days of the 7% protein diet. The epiphysis length was only minimally affected. 4. In experiment 2, food intake increased immediately on refeeding in all except the 3% protein fed group.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses to protein deficiency of plasma and tissue insulin-like growth factor-I levels and proteoglycan synthesis rates in rat skeletal muscle and bone.

The relative biological importance of plasma levels of insulin-like growth factors (IGFs) is uncertain since the IGFs may act through endocrine mechanisms involving circulating IGFs secreted by the liver, or by autocrine/paracrine mechanisms with IGF production in or close to their target cells. We report here studies in rats designed to examine this problem with an investigation of the changes in plasma and tissue concentrations of IGF-I in relation to the inhibition of bone and muscle growth and proteoglycan synthesis, a putative IGF-I-sensitive process, by protein deficiency. Over a 3-week period in young well-fed growing rats, there were marked increases in plasma IGF-I, whereas in the protein-deficient animals in which growth was inhibited concentrations fell markedly. In bone, concentrations of IGF-I were initially 20% of plasma, did not increase with age and were minimally influenced by protein deficiency. In skeletal muscle, concentrations of IGF-I were initially 3% of plasma, did not increase with age, but did fall with protein deficiency. In bone, the inhibition of proteoglycan synthesis by the protein deficiency was not correlated with changes in tissue IGF-I concentrations and was poorly correlated with changes in plasma hormone concentrations, although in the latter case an exponential relationship could be fitted to the data from the initial control and subsequent protein-deficient animals. In muscle, the changes in proteoglycan synthesis were significantly linearly correlated with changes in tissue IGF-I compared with an exponential relationship with plasma concentrations from the initial control and subsequent protein-deficient animals.(ABSTRACT TRUNCATED AT 250 WORDS)