Two pleiotropic classes of daf-2 mutation affect larval arrest, adult behavior, reproduction and longevity in Caenorhabditis elegans

The nematode Caenorhabditis elegans responds to overcrowding and scarcity of food by arresting development as a dauer larva, a nonfeeding, long-lived, stress-resistant, alternative third-larval stage. Previous work has shown that mutations in the genes daf-2 (encoding a member of the insulin receptor family) and age-1 (encoding a PI 3-kinase) result in constitutive formation of dauer larvae (Daf-c), increased adult longevity (Age), and increased intrinsic thermotolerance (Itt). Some daf-2 mutants have additional developmental, behavioral, and reproductive defects. We have characterized in detail 15 temperature-sensitive and 1 nonconditional daf-2 allele to investigate the extent of daf-2 mutant defects and to examine whether specific mutant traits correlate with each other. The greatest longevity seen in daf-2 mutant adults was approximately three times that of wild type. The temperature-sensitive daf-2 mutants fell into two overlapping classes, including eight class 1 mutants, which are Daf-c, Age, and Itt, and exhibit low levels of L1 arrest at 25.5 degrees. Seven class 2 mutants also exhibit the class 1 defects as well as some or all of the following: reduced adult motility, abnormal adult body and gonad morphology, high levels of embryonic and L1 arrest, production of progeny late in life, and reduced brood size. The strengths of the Daf-c, Age, and Itt phenotypes largely correlated with each other but not with the strength of class 2-specific defects. This suggests that the DAF-2 receptor is bifunctional. Examination of the null phenotype revealed a maternally rescued egg, L1 lethal component, and a nonconditional Daf-c component. With respect to the Daf-c phenotype, the dauer-defective (Daf-d) mutation daf-12(m20) was epistatic to daf-2 class 1 alleles but not the severe class 2 alleles tested. All daf-2 mutant defects were suppressed by the daf-d mutation daf-16(m26). Our findings suggest a new model for daf-2, age-1, daf-12, and daf-16 interactions.

Genes that regulate both development and longevity in Caenorhabditis elegans

The nematode Caenorhabditis elegans responds to conditions of overcrowding and limited food by arresting development as a dauer larva. Genetic analysis of mutations that alter dauer larva formation (daf mutations) is presented along with an updated genetic pathway for dauer vs. nondauer development. Mutations in the daf-2 and daf-23 genes double adult life span, whereas mutations in four other dauer-constitutive genes positioned in a separate branch of this pathway (daf-1, daf-4, daf-7 and daf-8) do not. The increased life spans are suppressed completely by a daf-16 mutation and partially in a daf-2; daf-18 double mutant. A genetic pathway for determination of adult life span is presented based on the same strains and growth conditions used to characterize Daf phenotypes. Both dauer larva formation and adult life span are affected in daf-2; daf-12 double mutants in an allele-specific manner. Mutations in daf-12 do not extend adult life span, but certain combinations of daf-2 and daf-12 mutant alleles nearly quadruple it. This synergistic effect, which does not equivalently extend the fertile period, is the largest genetic extension of life span yet observed in a metazoan.

The Caenorhabditis elegans dauer larva: developmental effects of pheromone, food, and temperature

Three environmental cues influence both the entry into and exit from the developmentally arrested dispersal stage called the dauer larva: a dauer-inducing pheromone, food, and temperature. The pheromone, which is a measure of population density, induces dauer larva formation at the second (L2) molt and inhibits recovery in a dose-dependent manner. Food acts competitively to reduce the frequency of dauer larva formation and to enhance recovery. The pheromone causes a specific extension of the second larval stage, coupled with a transient decrease in the growth rate of the L2. Second-stage larvae grown in the presence of added pheromone are morphologically distinguishable from L2 larvae grown without pheromone. We have named the pre-dauer L2 larva the L2d. Commitment to dauer larva formation can occur at the L2d molt. When L2d larvae are shifted out of pheromone to a lawn of E. coli just before the L2d molt, a few worms complete development into dauer larvae. In contrast, worms are essentially committed to the non-dauer life cycle by the first larval molt if the L1 larvae are not grown in appropriately high levels of pheromone. In the presence of pheromone, the percentage of dauer larva formation is enhanced at higher temperatures within the normal growth range. Temperature down-shifts induce dauer larva recovery. Temperature-shift experiments show that the enhancement of dauer larva formation requires exposure to the higher temperature around the L1 molt. Two sensory mutants defective in thermotaxis are altered in their sensitivity to the dauer-inducing pheromone, but their pheromone response retains temperature dependence. Response of dauer larvae to environmental cues is highly age dependent, with older dauer larvae exhibiting an increased tendency to recover.

Control of C. elegans larval development by neuronal expression of a TGF-beta homolog

The Caenorhabditis elegans dauer larva is specialized for dispersal without growth and is formed under conditions of overcrowding and limited food. The daf-7 gene, required for transducing environmental cues that support continuous development with plentiful food, encodes a transforming growth factor-beta (TGF-beta) superfamily member. A daf-7 reporter construct is expressed in the ASI chemosensory neurons. Dauer-inducing pheromone inhibits daf-7 expression and promotes dauer formation, whereas food reactivates daf-7 expression and promotes recovery from the dauer state. When the food/pheromone ratio is high, the level of daf-7 mRNA peaks during the L1 larval stage, when commitment to non-dauer development is made.

Interacting genes in nematode dauer larva formation

The dauer larva of Caenorhabditis elegans is a developmentally arrested stage induced by starvation or overcrowding. Mutant genes controlling the ability to form dauer larvae interact in a way which allows them to be ordered in a pathway. Mutant phenotypes suggest that the pathway corresponds to neural processing of environmental stimuli.

Sensitivity to change of the Roland-Morris Back Pain Questionnaire: part 1

BACKGROUND AND PURPOSE

This study estimated the Roland-Morris Back Pain Questionnaire's (RMQ) change score that best classified patients as those who had achieved an important change and those who had not achieved an important change. The study also investigated whether the estimate of change was dependent on patients' initial scores.

SUBJECTS AND METHODS

The RMQ was administered to 226 patients with low back pain of less than 6 weeks' duration during their initial visit for physical therapy and following 3 to 6 weeks of treatment. A global rating of change was used to classify patients as those who had changed an important amount and those who had not changed. Receiver operating characteristic curves were used to identify the RMQ change score that most accurately classified patients with respect to important change. This analysis was repeated for 5 overlapping subsamples of patients with initial scores 0 to 8, 5 to 12, 9 to 16, 13 to 20, and 17 to 24.

RESULTS

The area under the receiver operating characteristic curves increased when patients' initial scores were taken into account. Estimates of important change were 2, 4, 5, 8, and 8 for the initial score intervals mentioned above.

CONCLUSION AND DISCUSSION

Important change appears to be dependent on patients' initial RMQ scores. Subsequent inquiry using different hypotheses would add support to the estimates of important change found in this study.

Health status measures: strategies and analytic methods for assessing change scores

Over the last 15 years, numerous self-report health status measures have appeared in the literature. An important parallel development has been the development of numerous strategies for assessing change in health status over time. The purpose of this article is to summarize and critique the more common design and analytic strategies for assessing the meaningfulness of change over time. Five commonly reported designs are presented, critiqued, and depicted using examples from the literature. Methods for analyzing results are reviewed and illustrated using two data sets. Insights into comparing competing health status measures are provided. In summary, the article suggests that some designs and analytic strategies are more adept than others at assessing change and that these methods should be considered when planning sensitivity-to-change studies.

A pheromone influences larval development in the nematode Caenorhabditis elegans

A Caenorhabditis-specific pheromone and the food supply influence both entry into and exit from a developmentally arrested juvenile stage called the dauer larva. The pheromone increases the frequency of dauer larva formation and inhibits recovery but does not affect adult behavior such as chemotaxis and egg laying. The fatty acid--like pheromone has been partially purified and characterized by a new bioassay. If similar developmental control mechanisms are used by parasitic nematodes, such mechanisms might be exploited to develop highly selective anthelmintic agents.

The daf-4 gene encodes a bone morphogenetic protein receptor controlling C. elegans dauer larva development

The bone morphogenetic protein (BMP) family is a conserved group of signalling molecules within the transforming growth factor-beta (TGF-beta) superfamily. This group, including the Drosophila decapentaplegic (dpp) protein and the mammalian BMPs, mediates cellular interactions and tissue differentiation during development. Here we show that a homologue of human BMPs controls a developmental switch in the life cycle of the free-living soil nematode Caenorhabditis elegans. Starvation and overcrowding induce C. elegans to form a developmentally arrested, third-stage dauer larva. The daf-4 gene, which acts to inhibit dauer larva formation and promote growth, encodes a receptor protein kinase similar to the daf-1, activin and TGF-beta receptor serine/threonine kinases. When expressed in monkey COS cells, the daf-4 receptor binds human BMP-2 and BMP-4. The daf-4 receptor is the first to be identified for any growth factor in the BMP family.

Goniometric reliability in a clinical setting. Shoulder measurements

The purpose of this study was to examine the intratester and intertester reliabilities for clinical goniometric measurements of shoulder passive range of motion (PROM) using two different sizes of universal goniometers. Patients were measured without controlling therapist goniometric placement technique or patient position during measurements. Repeated PROM measurements of shoulder flexion, extension, abduction, shoulder horizontal abduction, horizontal adduction, lateral (external) rotation, and medial (internal) rotation were taken of two groups of 50 subjects each. The intratester intraclass correlation coefficients (ICCs) for all motions ranged from .87 to .99. The ICCs for the intertester reliability of PROM measurements of horizontal abduction, horizontal adduction, extension, and medial rotation ranged from .26 to .55. The intertester ICCs for PROM measurements of flexion, abduction, and lateral rotation ranged from .84 to .90. Goniometric PROM measurements for the shoulder appear to be highly reliable when taken by the same physical therapist, regardless of the size of the goniometer used. The degree of intertester reliability for these measurements appears to be range-of-motion specific.

Reliability of goniometric measurements and visual estimates of knee range of motion obtained in a clinical setting

The purpose of this study was to examine the intratester and intertester reliability for goniometric measurements of knee flexion and extension passive range of motion (PROM). In addition, parallel-forms reliability for PROM measurements of the knee obtained by use of a goniometer and by visual estimation was examined. The intertester reliability for visual estimates of the PROM of the knee was also examined. Repeated measurements were obtained on 43 patients in a clinical setting. The intraclass correlation coefficients (ICCs) for intratester reliability of measurements obtained with a goniometer were .99 for flexion and .98 for extension. Intertester reliability for measurements obtained with a goniometer was .90 for flexion and .86 for extension. The ICCs for parallel-forms reliability for measurements obtained with a goniometer and by visual estimation ranged from .82 to .94. The intertester reliability for measurements obtained by visual estimation was .83 for flexion and .82 for extension. Results suggest clinicians should use a goniometer to take repeated PROM measurements of a patient's knee to minimize the error associated with these measurements.

daf-1, a C. elegans gene controlling dauer larva development, encodes a novel receptor protein kinase

The dauer larva is a developmentally arrested, non-feeding dispersal stage normally formed in response to overcrowding and limited food. The daf-1 gene specifies an intermediate step in a hierarchy of genes thought to specify a pathway for neural transduction of environmental cues. Mutations in daf-1 result in constitutive formation of dauer larvae even in abundant food. This gene has been cloned by Tc1-transposon tagging, and it appears to encode a new class of serine/threonine kinase. A daf-1 probe detects a 2.5 kb mRNA of low abundance, and the DNA sequence indicates that the gene encodes a 669 amino acid protein, with a putative transmembrane domain and a C-terminal protein kinase domain most closely related to the cytosolic, raf proto-oncogene family. Hence, the daf-1 product appears to be a cell-surface receptor required for transduction of environmental signals into an appropriate developmental response.

Mutations affecting the chemosensory neurons of Caenorhabditis elegans

We have identified and characterized 95 mutations that reduce or abolish dye filling of amphid and phasmid neurons and that have little effect on viability, fertility or movement. Twenty-seven mutations occurred spontaneously in strains with a high frequency of transposon insertion. Sixty-eight were isolated after treatment with EMS. All of the mutations result in defects in one or more chemosensory responses, such as chemotaxis to ammonium chloride or formation of dauer larvae under conditions of starvation and overcrowding. Seventy-five of the mutations are alleles of 12 previously defined genes, mutations which were previously shown to lead to defects in amphid ultrastructure. We have assigned 20 mutations to 13 new genes, called dyf-1 through dyf-13. We expect that the genes represented by dye-filing defective mutants are important for the differentiation of amphid and phasmid chemosensilla.

Genetic, behavioral and environmental determinants of male longevity in Caenorhabditis elegans

Males of the nematode Caenorhabditis elegans are shorter lived than hermaphrodites when maintained in single-sex groups. We observed that groups of young males form clumps and that solitary males live longer, indicating that male-male interactions reduce life span. By contrast, grouped or isolated hermaphrodites exhibited the same longevity. In one wild isolate of C. elegans, AB2, there was evidence of copulation between males. Nine uncoordinated (unc) mutations were used to block clumping behavior. These mutations had little effect on hermaphrodite life span in most cases, yet many increased male longevity even beyond that of solitary wild-type males. In one case, the neuronal function mutant unc-64(e246), hermaphrodite life span was also increased by up to 60%. The longevity of unc-4(e120), unc-13(e51), and unc-32(e189) males exceeded that of hermaphrodites by 70-120%. This difference appears to reflect a difference in sex-specific life span potential revealed in the absence of male behavior that is detrimental to survival. The greater longevity of males appears not to be affected by daf-2, but is influenced by daf-16. In the absence of male-male interactions, median (but not maximum) male life span was variable. This variability was reduced when dead bacteria were used as food. Maintenance on dead bacteria extended both male and hermaphrodite longevity.

Changes in gene expression associated with developmental arrest and longevity in Caenorhabditis elegans

Gene expression in a developmentally arrested, long-lived dauer population of Caenorhabditis elegans was compared with a nondauer (mixed-stage) population by using serial analysis of gene expression (SAGE). Dauer (152,314) and nondauer (148,324) SAGE tags identified 11,130 of the predicted 19,100 C. elegans genes. Genes implicated previously in longevity were expressed abundantly in the dauer library, and new genes potentially important in dauer biology were discovered. Two thousand six hundred eighteen genes were detected only in the nondauer population, whereas 2016 genes were detected only in the dauer, showing that dauer larvae show a surprisingly complex gene expression profile. Evidence for differentially expressed gene transcript isoforms was obtained for 162 genes. H1 histones were differentially expressed, raising the possibility of alternative chromatin packaging. The most abundant tag from dauer larvae (20-fold more abundant than in the nondauer profile) corresponds to a new, unpredicted gene we have named tts-1 (transcribed telomere-like sequence), which may interact with telomeres or telomere-associated proteins. Abundant antisense mitochondrial transcripts (2% of all tags), suggest the existence of an antisense-mediated regulatory mechanism in C. elegans mitochondria. In addition to providing a robust tool for gene expression studies, the SAGE approach already has provided the advantage of new gene/transcript discovery in a metazoan.

Longevity in Caenorhabditis elegans reduced by mating but not gamete production

Theories of life-history evolution propose that trade-offs occur between fitness components, including longevity and maximal reproduction. In Drosophila, female lifespan is shortened by increased egg production, receipt of male accessory fluid and courting. Male lifespan is also reduced by courting and/or mating. Here we show that in the nematode Caenorhabditis elegans, mating with males reduces the lifespan of hermaphrodites by a mechanism independent of egg production or receipt of sperm. Conversely, males appear unaffected by mating. Thus, in C. elegans there is no apparent trade-off between longevity and increased egg or sperm production, but there is a substantial cost to hermaphrodites associated with copulation.

A pheromone-induced developmental switch in Caenorhabditis elegans: Temperature-sensitive mutants reveal a wild-type temperature-dependent process

Formation of a developmentally arrested dispersal stage called the dauer larva is enhanced by a Caenorhabditis-specific pheromone and is inhibited by increasing amounts of food. Pheromone-induced dauer larva formation of three tested wild-type strains is temperature-dependent, so that an increased percentage of the population forms dauer larvae at 25 degrees C compared to lower temperatures. Dauer-defective mutants fail to respond to added pheromone, and some behavioral mutants affected in thermotaxis or egg-laying also exhibit abnormal responses. Temperature-sensitive (ts) dauer-constitutive mutants form dauer larvae at a restrictive temperature regardless of environmental stimuli. At the permissive temperature (17.5 degrees C), alleles of six out of seven dauer-constitutive genes tested overrespond to the dauer-inducing pheromone. All known mutations in daf-4 (eight alleles) and daf-7 (five alleles) produce a ts dauer-constitutive phenotype. One daf-4 and one daf-7 allele are suppressed by the amber nonsense suppressor, sup-7(st5). At least these two dauer-constitutive mutations are likely to cause production of nonfunctional rather than ts gene products. These mutations appear to indirectly result in a ts phenotype by enhancing the expression of a wild-type ts developmental process.

Functional study of the Caenorhabditis elegans secretory-excretory system using laser microsurgery

Individual cells of the Caenorhabditis elegans secretory-excretory system were ablated by laser microbeam in various larval stages. Effects on growth, molting, osmoregulation, fertility, longevity, and dauer larva formation were tested. Single-cell ablations did not prevent subsequent molting, but ablation of the pore cell or the duct cell resulted in the absence of the normal cuticular lining of the excretory duct following a molt. When the pore cell, duct cell, or excretory cell was ablated, the animals filled with fluid within 12-24 hr and died within a few days, producing very few progeny. Ablation of the excretory gland cell, on the other hand, had no obvious developmental or behavioral effects. Excretory activity was monitored in dauer larvae by observing pulsation of the excretory duct in conditions of differing osmolarity. The rate of pulsation was quite variable over time in conditions of low osmotic strength, but average five- to six-fold higher than that observed in buffered saline. These observations, combined with the effects of laser ablation, lead to the conclusion that one function of the excretory system is osmoregulation.

Sensory control of dauer larva formation in Caenorhabditis elegans

As a sensory response to starvation or overcrowding, Caenorhabditis elegans second-stage larvae may molt into a developmentally arrested state called the dauer larva. When environmental conditions become favorable for growth, dauer larvae mold and resume development. Some mutants unable to form dauer larvae are simultaneously affected in a number of sensory functions, including chemotaxis and mating. The behavior and sensory neuroanatomy of three such mutants, representing three distinct genetic loci, have been determined and compared with wild-type strain. Morphological abnormalities in afferent nerve endings were detected in each mutant. Both amphid and outer labial sensilla are affected in the mutant CB1377 (daf-6)X, while another mutant, CB1387 (daf-10)IV, is abnormal in amphidial cells and in the tips of the cephalic neurons. The most pleitropic mutant, CB1379 (che-3)I, exhibits gross abnormalities in the tips of virtually all anterior and posterior sensory neurons. The primary structural defect in CB1377 appears to be in the nonneuronal amphidial sheath cells. The disruption of neural organization in CB1377 is much greater in the adult than in the L2 stage. Of all the anterior sense organs examined, only the amphids are morphologically affected in all three mutants. Thus, one or more of the amphidial neurons may mediate the sensory signals for entry into the dauer larva stage in normal animals. Using temperature-sensitive mutants we determined that the same defects which block entry into the dauer stage also prevent recovery of dauer larvae.

Sensitivity to change of the Roland-Morris Back Pain Questionnaire: part 2

BACKGROUND AND PURPOSE

One purpose of this study was to determine whether the Roland-Morris Back Pain Questionnaire (RMQ) could be used to detect clinically meaningful change in individual patients. The construct that served as the basis for this study was that RMQ change scores should be greater for patients meeting their treatment goals than for patients who did not meet their goals. The second purpose of the study was to determine whether sensitivity to change (STC) varies depending on the magnitude of the initial RMQ score.

SUBJECTS AND METHODS

Of the 143 patients with low back pain who completed the study, 104 patients achieved their goals and 39 patients did not achieve their goals. Receiver operating characteristic (ROC) curve analysis and likelihood ratios were used to determine the RMQ change scores that best classify patients as having met or not met their goals.

RESULTS

The area under the ROC curve for the entire RMQ scale was 0.68, while the curve areas for smaller RMQ intervals varied from 0.80 to 0.97.

CONCLUSION AND DISCUSSION

The STC for the entire RMQ scale was poor for the construct examined in this study. The likelihood ratios for smaller RMQ intervals support the construct validity of the RMQ for assessing change in disability. Initial RMQ score magnitudes must be taken into account to improve the rate of making correct predictions about whether meaningful change in disability will occur following treatment.

Fine structure of the Caenorhabditis elegans secretory-excretory system

The secretory-excretory system of C. elegans, reconstructed from serial-section electron micrographs of larvae, is composed of four cells, the nuclei of which are located on the ventral side of the pharynx and adjacent intestine. (1) The pore cell encloses the terminal one-third of the excretory duct which leads to an excretory pore at the ventral midline. (2) The duct cell surrounds the excretory duct with a lamellar membrane from the origin of the duct at the excretory sinus to the pore cell boundary. (3) A large H-shaped excretory cell extends bilateral canals anteriorly and posteriorly nearly the entire length of the worm. The excretory sinus within the cell body joins the lumena of the canals with the origin of the duct. (4) A binucleate, A-shaped gland cell extends bilateral processes anteriorly from cell bodies located just behind the pharynx. These processes are fused at the anterior tip of the cell, where the cell enters the circumpharyngeal nerve ring. The processes are also joined at the anterior edge of the excretory cell body, where the excretory cell and gland are joined to the duct cell at the origin of the duct. Secretory granules may be concentrated in the gland near this secretory-excretory junction. Although the gland cells of all growing developmental stages stain positively with paraldehyde-fuchsin, the gland of the dauer larva stage (a developmentally arrested third-stage larva) does not stain, nor do glands of starved worms of other stages. Dauer larvae uniquely lack secretory granules, and the gland cytoplasm is displaced by a labyrinth of large, transparent spaces. Exit from the dauer stage results in the return of active secretory morphology in fourth-stage larvae.

Use of generic versus region-specific functional status measures on patients with cervical spine disorders

BACKGROUND AND PURPOSE

Few data exist to support the use of functional status measures on patients with disorders of the cervical spine. This study was designed to compare the construct validity and sensitivity to change of the Neck Disability Index (NDI) and the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36).

SUBJECTS AND METHODS

Patients (N = 146) with a variety of disorders of the cervical spine completed the NDI and the SF-36 prior to treatment. Following discharge from treatment, 69 of these patients completed a second NDI and SF-36.

RESULTS

There was evidence for the construct validity and sensitivity to change of the NDI and the physical and mental component scores of the SF-36. The ability of the NDI and SF-36 to detect change varied, depending on the construct tested. The SF-36 was superior in some instances, and the NDI was superior in other instances. The NDI appears to measure both mental and physical health-related factors.

CONCLUSION AND DISCUSSION

There appears to be substantial overlap between the 2 measures. The use of both measures, therefore, is probably not necessary. [Riddle DL, Stratford PW. Use of generic versus region-specific functional measures on patients with cervical spine disorders.

The shoulder pain and disability index: the construct validity and responsiveness of a region-specific disability measure

BACKGROUND AND PURPOSE

The purposes of this study were (1) to assess the construct validity of the Shoulder Pain and Disability Index (SPADI) and (2) to determine whether the SPADI is more responsive than the Sickness Impact Profile (SIP), a generic health status measure.

SUBJECTS

The sample consisted of 94 patients who were diagnosed with a shoulder problem and referred to six outpatient physical therapy clinics.

METHODS

Clinically meaningful change was determined by use of an ordinal rating scale designed to determine whether the patient's shoulder function was improved, the same, or worse following treatment. Spearman rho correlations were calculated for the initial visit SPADI and SIP scores. The standardized response mean (SRM) was used to measure responsiveness for the patients who were judged to be improved. One-tailed paired t tests (alpha = .01) were used to determine whether differences existed among SRM values.

RESULTS

Correlations between the SPADI and SIP scores ranged from r = .01 to r = .57. The SRM value was higher for the SPADI total score (SRM = 1.38) than for the SIP total score (SRM = 0.79).

CONCLUSION AND DISCUSSION

Most correlations between SPADI and SIP scores provided support for the construct validity of the SPADI. The SPADI does not appear to strongly reflect occupational and recreational disability and is more responsive than the SIP.