Biomedical subjects

B F Mitchell

Publications and source records attributed to B F Mitchell.

At least 19 recordsLinked to original sources

PubMed2006

Decidual activation: abundance and localization of prostaglandin F2alpha receptor (FP) mRNA and protein and uterine activation proteins in human decidua at preterm birth and term birth.

OBJECTIVE: To study how the decidua contributes to parturition, we examined prostaglandin F(2alpha) concentrations as well as prostaglandin 15-hydroxy dehydrogenase, prostaglandin F(2alpha) receptor, matrix metalloproteinases 2 and 9, oxytocin receptor, prostaglandin-H synthase-2, and the prostaglandin E(2) receptor expression in human decidua. MATERIALS AND METHODS: Decidual samples were isolated from placentas collected from patients at preterm not in labor (PTNIL), preterm labor (PTL), term not in labor (TNIL), and term labor (TL). For immunohistochemistry, fresh membranes which included chorion, amnion and decidua from term patients were collected. RESULTS: Prostaglandin F(2alpha) receptor mRNA was low in all preterm patients and then significantly increased towards term (p=0.049). Prostaglandin F(2alpha) receptor protein was identified in the amnion epithelium and mesoderm, chorion trophoblasts and decidua by immunohistochemistry, and levels were highest at TNIL (p=0.007) as measured by western blot. Prostaglandin F(2alpha) levels were higher at PTNIL than TNIL. Matrix metalloproteinases 2 and 9 protein and pro-enzyme activities were higher at TL than TNIL. There were no significant changes among the groups for any of the other factors measured. CONCLUSIONS: These results suggest that the induction of Prostaglandin F(2alpha) receptor at term may facilitate the decidua contribution to parturition, and its regulation and role should be examined further.

DNA Primers↗

PubMed2006

Phorbol ester treatment of human myometrial cells suppresses expression of oxytocin receptor through a mechanism that does not involve activator protein-1.

Oxytocin (OT) is a potent uterine agonist. Its receptor (OTR) is a G protein-coupled receptor that is downregulated by prolonged exposure to OT. We hypothesized that activation of PKC mediated this OT-induced decrease in OTR expression. Diminished PKC activity in late pregnancy could underlie the increased expression of uterine OTR preceding labor onset. Using cell cultures of transformed human uterine myocytes, we determined the effects of PKC agonists and antagonists on the expression of OTR. We also explored the effects of overexpression of activator protein-1 (AP-1, a mediator of many PKC- and phorbol ester-induced effects) using adenoviral expression vectors for the AP-1 subunits c-Jun and c-Fos. Stimulation of PKC using the phorbol ester 12-O-tetradecanoylphorbol 13-acetate caused a rapid, significant (P < or = 0.05) increase in c-Jun and c-Fos concentrations but a significant decrease in mRNA for OTR within 6 h followed by a significant decrease in OT binding by 24 h. Adenoviral infection of the cells with expression vectors for c-Jun and c-Fos increased the AP-1 subunits but had no effect on OTR expression. Furthermore, there were no changes in c-Fos or c-Jun levels in human intrauterine tissues around the time of labor onset, as measured by Western analyses. We conclude that phorbol ester treatment decreases OTR expression, likely through a mechanism that does not involve AP-1.

Blood Proteins↗

PubMed2006

Perspectives on the management of the short cervix identified by transvaginal ultrasound during pregnancy: an update for Canadian obstetrical caregivers.

A shortened cervix is often considered to be equivalent to cervical insufficiency, and a cerclage may be offered as an intervention to prolong pregnancy; however, we may not be differentiating between true cervical insufficiency and intrauterine causes of cervical shortening. A recent meta-analysis found no significant reduction in preterm birth < 35 weeks' gestation in women with cerclage compared with no cerclage in the total population of women studied. However, there was a potentially significant reduction in preterm birth < 35 weeks among women with a singleton pregnancy (relative risk [RR] 0.74; 95% confidence intervals [CI] 0.57-0.96), with a singleton pregnancy and a previous preterm birth (RR 0.61; 95% CI 0.40-0.92), and with a singleton pregnancy with a previous mid-trimester loss (RR 0.57; 95% CI 0.33-0.99). An increase was found in preterm birth among twin gestations with cerclage placed for a shortened cervix on transvaginal ultrasound (RR 2.15; 95% CI 1.15-4.01). This unexpected finding underscores the possibility of harm with this intervention. This intervention deserves further study. A national registry or database would allow us to identify women who may benefit more significantly from cerclage by collecting data on possible confounding effects such as concomitant intrauterine infection or placental disease.

Canada↗

PubMed2005

Proinflammatory cytokines inhibit human placental 11beta-hydroxysteroid dehydrogenase type 2 activity through Ca2+ and cAMP pathways.

Excessive fetal exposure to glucocorticoids has been implicated in the etiology of adult metabolic and cardiovascular disease. Placental 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) may protect the fetus from excessive glucocorticoid exposure. Maternal stress may be accompanied by elevated levels of cortisol and increased proinflammatory cytokines [interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha)]. We hypothesize that proinflammatory cytokines inhibit human placental 11beta-HSD activity. We incubated explant cultures of term human placental villi in the presence or absence of 10 ng/ml IL-1beta, IL-6, or TNF-alpha, with or without agonists or antagonists of intracellular Ca2+ and adenylyl cyclase. Activity for 11beta-HSD2 was estimated using a radioisotope assay, and mRNA was measured using quantitative RT-PCR. All cytokines significantly (P < or = 0.05) reduced 11beta-HSD2 activity (>75% suppression); maximal inhibition occurred within 2 h and was maintained for at least 24 h. The IL-1beta-induced inhibitory activity was attenuated using a Ca2+ channel blocker (nifedipine), an intracellular Ca2+ antagonist [8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate], or the adenylyl cyclase stimulant forskolin. Conversely, 11beta-HSD2 activity was diminished in the presence of the Ca2+ ionophore A-23187 or the adenylyl cyclase inhibitor SQ-22536. mRNA levels for 11beta-HSD2 were not changed by any of the treatments. Proinflammatory cytokines inhibit human placental 11beta-HSD2 activity through a mechanism that involves increased intracellular Ca2+ and inhibition of adenylyl cyclase. This could result in excessive fetal exposure to maternal cortisol. This mechanism might mediate part of the increased risk of metabolic and cardiovascular disease in adult offspring.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗

PubMed2004

Resistance exercise decreases the need for insulin in overweight women with gestational diabetes mellitus.

OBJECTIVE: This study examines the effects of circuit-type resistance training on the need for insulin in women with gestational diabetes mellitus. STUDY DESIGN: Thirty-two patients with gestational diabetes mellitus were randomly assigned either to a group that was treated with diet alone or to a group that was treated with diet plus resistance exercise. RESULTS: The number of women whose condition required insulin therapy was the same, regardless of treatment. However, a subgroup analysis that examined only overweight women (prepregnant body mass index, >25 kg/m(2)) showed a lower incidence of insulin use in the diet-plus-exercise group (P<.05). Women in the diet-plus-exercise group were prescribed less insulin (P<.05) and showed a longer delay from diagnosis to the initiation of insulin therapy (P<.05), compared with the diet-alone group. CONCLUSION: Resistance exercise training may help to avoid insulin therapy for overweight women with gestational diabetes mellitus.

Adult↗

PubMed2003

Parathyroid hormone-related protein treatment of pregnant rats delays the increase in connexin 43 and oxytocin receptor expression in the myometrium.

Myometrial quiescence during pregnancy is maintained by progesterone, which suppresses the expression of labor-associated genes such as connexin 43 (Cx43) and the oxytocin receptor (OTR). Parathyroid hormone-related protein (PTHrP) is a smooth muscle relaxant that inhibits myometrial contractions and therefore may act in synergy with progesterone to maintain myometrial quiescence during late pregnancy. We investigated the possibility that PTHrP, like progesterone, could act to suppress the expression of labor-associated genes. Pregnant rats were treated starting on Day 19 with daily i.p. injections of 100 microg/kg PTHrP (human synthetic fragment 1-34). On Day 22 of gestation, there was a significant reduction in the expression of Cx43 (mRNA and protein) and OTR (mRNA) in the myometrium of PTHrP-treated animals, whereas on Day 23 (labor) the expression of both Cx43 and OTR was unchanged by PTHrP treatment. Treatment of pregnant rats with PTHrP did not affect the time of delivery, concentrations of progesterone in maternal plasma, or levels of c-fos, fra-2, or parathyroid hormone/PTHrP receptor mRNA on any gestational day. Because PTHrP treatment delayed the dramatic increase in the expression of Cx43 and OTR, it may be an important factor in the maintenance of the quiescent state of the myometrium at a time when the concentrations of progesterone in maternal circulation decrease. PTHrP treatment did not prevent the increase in Cx43 and OTR gene expression on Day 23 or the timing of labor, suggesting that the effects of PTHrP signaling are overridden with the onset of labor.

Animals↗

PubMed2003

Myometrial activation and preterm labour: evidence supporting a role for the prostaglandin F receptor--a review.

An increase in the myometrial expression of the prostaglandin (PG) receptors, and especially the PGF(2alpha) receptor (FP), may be an important component of the process initiating preterm labour. In this review of the literature and presentation of new possibilities, evidence will be discussed that demonstrates an increase in mouse uterine FP mRNA occurs at preterm birth whereas uterine PGF(2alpha) concentrations do not increase, suggesting elevated uterine receptor expression and sensitivity is a mechanism for preterm labour initiation. The first examination of the complete human myometrial FP promoter will be described and evidence presented that demonstrates the pro-inflammatory cytokine, interleukin-1beta, stimulates FP mRNA expression. Finally new data showing that administration of a specific FP antagonist delays preterm birth in sheep will be presented.

Animals↗

PubMed2002

Messenger RNA for progesterone receptor isoforms in the late-gestation rat uterus.

The progesterone receptor (PR) has three isoforms, PR-A, PR-B, and PR-C, which have different physiological effects. PR-A may inhibit PR-B-mediated transcription. Parturition requires withdrawal of progesterone (P4). This could occur through decreased P4 concentrations and/or a change in PR isoforms to diminish the effect of P4. We measured mRNA for PR isoforms in rat uterine tissues through late gestation and investigated the effects of antagonists to estrogen (tamoxifen) and P4 (RU-486). Two specific probes were used for ribonuclease protection assays; one (PR-total) measured PR-A, PR-B, and PR-C, and the other recognized only PR-B. PR-total mRNA increased significantly through late gestation, whereas PR-B was unchanged. The ratio of PR-total to PR-B peaked on the day before parturition. Tamoxifen delayed parturition and inhibited the increase in PR-total without affecting PR-B mRNA. RU-486 caused early parturition associated with increased PR-total mRNA, with no change in PR-B. We conclude that there are significant changes in PR isoforms in late-gestation rat uterus. These changes may be regulated by estrogen and P4 and may influence the timing of parturition.

Animals↗

PubMed2002

Oxytocin does not directly affect vascular tone in vessels from nonpregnant and pregnant rats.

Recent evidence suggests oxytocin (OT) may regulate vascular tone. OT and its receptor (OTR) have been identified in the rat heart and great vessels. Expression of OT and OTR is increased in some tissues during pregnancy. We hypothesized that the OT/OTR system may be a physiological regulator of vascular tone and mediate the decreased vascular resistance noted during pregnancy. Using a wire myograph system, we measured changes in vascular tone in response to OT in small mesenteric arteries, uterine arcuate arteries, and thoracic aorta from nonpregnant and pregnant rats. Additionally, we used reverse transcriptase-polymerase chain reaction (RT-PCR) to measure mRNA for OTR in these vascular tissues. Although OTR mRNA was identified by RT-PCR, OT did not elicit a vasodilatory effect in any of the vessels studied. High concentrations of OT (>10(-8) M) caused vasoconstriction that was eliminated by a specific vasopressin V(1a) receptor antagonist. Although it may have an indirect effect in regulation of peripheral resistance, we conclude that OT is unlikely to play a direct role in the physiological regulation of vascular tone.

Animals↗

PubMed2001

In-home nursing care for women with high-risk pregnancies: outcomes and cost.

OBJECTIVE: To evaluate a program that provides in-home care to women with pregnancies threatened by preterm delivery (including preterm labor, preterm premature rupture of membranes, and multiple gestation) and women with pregnancy-related hypertension. METHODS: Data from hospital discharge summaries were used to compare birth outcomes and cost of care for women in the in-home program and a cohort of women who received in-hospital antenatal care before the new program. Birth outcomes included data for mothers and infants. The sample included 437 women with threatened preterm delivery (n = 228 in-home, n = 209 in-hospital) and 308 with hypertension (n = 155 in-home, n = 153 in-hospital). The cost per woman included all costs of services for mothers and infants. RESULTS: Women at risk of preterm delivery who received in-home care were half as likely to have their infants in the neonatal intensive care unit more than 48 hours (odds ratio 0.53, 95% confidence interval 0.36, 0.78). On average, their infants weighed more (2732 +/- 716 g versus 2330 +/- 749 g, P <.001) and were 2 weeks older at birth (36.1 +/- 3.1 weeks versus 34.0 +/- 4.0 weeks, P <.001). There was a wide range in the total cost per woman and no significant difference between cohorts. For women with hypertension, there were no significant differences between in-home and in-hospital cohorts in birth outcomes or costs of care per woman. CONCLUSION: The program with current admission criteria, staffing, and guidelines for antenatal hospital admission provides safe care to women at similar cost to that of hospitalization.

Adult↗

PubMed2001

Transcriptional regulation of oxytocin receptor by interleukin-1beta and interleukin-6.

The up-regulation of oxytocin (OT) receptors in late pregnancy results principally from increased synthesis of messenger RNA. The 5'-flanking region of the human OT receptor gene contains several putative binding sites for nuclear factor-interleukin-6 (NF-IL6), also known as CAAT/enhancer binding protein-beta. This trans-acting factor modulates the expression of genes involved in acute inflammatory responses. Proinflammatory cytokines, such as IL-1beta or IL-6, have been implicated as mediators in both preterm and term labor, particularly in association with intrauterine infection. We hypothesized that IL-1beta and IL-6 induce OT receptor gene expression in human myometrial cells, and this is mediated by NF-IL6 and cognate response elements in the 5'-flanking region of the OT receptor gene. Contrary to the hypothesis, both IL-1beta and IL-6 treatment resulted in a significant decrease in OT receptor messenger RNA measured by ribonuclease protection analysis. Using electrophoretic mobility shift assay, we have shown that NF-IL6 is present at low levels that appear to be increased after treatment with either IL-1beta or IL-6. Using deletion analysis and functional transfection studies in HeLa cells, we demonstrated that the OT receptor gene promoter displays constitutive basal activity and is negatively regulated by both IL-1beta and IL-6. This suppressive ability of IL-1beta and IL-6 depends on the -1203/-722 region of the OT receptor promoter, which contains binding sites for NF-IL6, acute phase response element, and NF-kappaB. Our findings suggest a role for IL-1beta and IL-6 in the transcriptional regulation of the human OT receptor gene.

5' Untranslated Regions↗

PubMed2000

Effects of LPS and IL-6 on oxytocin receptor in non-pregnant and pregnant rat uterus.

PROBLEM: Little is known regarding the regulation of the timing of parturition. Recent evidence suggests an interaction between the immune system and uterine contractility in late gestation. METHOD: Pregnant rats were treated with LPS in vivo in attempts to establish a model of premature parturition induced by the pro-inflammatory response. Uterine explants were incubated in vitro to determine the effects of IL-6 on uterine synthesis of oxytocin (OT) and its receptor (OTR). RESULTS: LPS injection was quite toxic to pregnant rats and gave extremely variable results. In animals that delivered, there was a marked increase in the uterine concentrations of OTR and OTR mRNA. There was no consistent effect regarding the timing of parturition. IL-6 caused a significant increase in the concentration of OTR mRNA in uterine explants from pregnant rats but not in tissues from non-pregnant animals. CONCLUSION: Rat uterine concentrations of OTR are regulated by IL-6. Pro-inflammatory cytokines may stimulate uterine contractility in late gestation rat uterine tissues through a mechanism involving stimulation of OTR.

Animals↗

PubMed1999

Morbidity assessment index for newborns: a composite tool for measuring newborn health.

OBJECTIVE: The objective was to develop, validate, and recommend a scaling model for a discriminative obstetric outcome measure named the Morbidity Assessment Index for Newborns. The purpose of this tool is to allow comparison of obstetric therapeutic strategies on neonatal morbidity, particularly in the mild to moderate morbidity range. STUDY DESIGN: A list of 66 check-mark (yes or no) items of readily available clinical and laboratory data from the early neonatal period was compiled by a panel of obstetric and neonatal experts. These data were collected on 411 neonates born at >/=28 weeks' gestation and representing all grades of morbidity. Detailed psychometric testing included dimensionality testing and item analysis with the item response theory. The scores obtained with this new assessment tool were correlated with newborn and maternal disease conditions or events and with other measures of newborn morbidity. RESULTS: The Morbidity Assessment Index for Newborns is easy to apply in prospective or retrospective studies. Detailed psychometric evaluation resulted in modification of the list to 47 items, each item with a relative scale value according to severity of morbidity. The test was demonstrated to be a reliable and generalizable scaled index that performs optimally for the mild to moderate neonatal morbidity range. CONCLUSION: The Morbidity Assessment Index for Newborns is a validated outcome measurement scale of neonatal morbidity. This new tool may facilitate the conduct of obstetric clinical trials or epidemiologic population-based studies in obstetrics.

Birth Weight↗

PubMed1998

Role of carboxy-extended forms of oxytocin in the rat uterus in the process of parturition.

The hypothalamic synthetic pathway of oxytocin (OT) involves the synthesis of carboxy-extended forms that serve as intermediate prohormones. We hypothesized that extended forms of OT are synthesized in the late-gestational rat uterus and that they compete for OT receptor binding. Parturition occurs only when the ratio of OT to its extended forms reaches a critical level. We have measured OT and its extended forms using two antisera, one recognizing OT and its extended forms, the other recognizing only mature amidated OT. Uterine tissue concentrations of extended forms of OT were 5- to 30-fold greater than those of OT, and both increased progressively and significantly through late gestation. The ratio of OT to its extended forms did not change significantly. Antagonists of estrogen or progesterone receptors reduced concentrations of extended forms by > 90% and of OT by 50%, though the estrogen antagonist significantly prolonged gestation and the progesterone antagonist induced preterm delivery. Using a muscle bath preparation, extended forms of OT were weak uterine stimulants and did not alter the OT concentration-response curves. Extended forms of OT were two to three orders of magnitude less able than OT to displace radiolabeled OT from late-gestational uterine binding sites. We conclude that uterine carboxy-extended OT prohormones are regulated in part by estrogen and progesterone. However, these extended forms of OT have little direct biological activity and do not compete with OT for receptor binding. Their role in the process of parturition may be confined to acting as substrates for OT synthesis.

Animals↗

PubMed1998

Oxytocin: a paracrine hormone in the regulation of parturition?

The role of oxytocin in parturition is controversial. When considered as an endocrine hormone, the balance of evidence suggests that oxytocin has little involvement in the initiation of labour. However, recent research has demonstrated synthesis of mRNA encoding oxytocin within the pregnant human uterus. This article reviews the hypothesis that oxytocin is an important paracrine (or autocrine) hormone with respect to the control of myometrial contractility in late gestation. Experimental data are provided from humans when possible and from studies using the rat as an experimental model. The processing of oxytocin prohormones in uterine tissues is reviewed and the presence and possible role of carboxy-extended forms of oxytocin in late gestational tissues of rats are discussed. The regulation of oxytocin and its receptor, particularly by oestrogen and progesterone, is reviewed. The inter-relationship between oxytocin and prostaglandins is discussed. Finally, the metabolism of oxytocin within intrauterine tissues and the recent development of specific antagonistic analogues to oxytocin are considered. It is concluded that further clarification of this paracrine system within intrauterine tissues during late gestation could lead to more successful strategies for preventing or arresting preterm labour in women.

Animals↗

PubMed1997

Metabolism of oxytocin in rat uterus and placenta in late gestation.

Concentrations of oxytocin (OT) peptide increase in rat uterine tissues at the time of parturition. We have measured the rate of OT metabolism in these tissues in late gestation to determine whether a decrease in OT catabolism is responsible for the increase in OT concentrations. Uterine and placental tissues were obtained from groups of rats at Days 16, 19, 21, 21.5, 22, and after delivery of the first pup. Delivery usually occurs in the early afternoon of Day 22. Some animals were treated with the estrogen receptor blocker tamoxifen, which will delay parturition by approximately 24 h. Cytosolic and microsomal preparations obtained using ultracentrifugation were incubated with radiolabeled OT. Metabolites were separated using HPLC, and enzyme kinetic parameters were calculated. OT was actively metabolized in both uterine and placental tissues. Total oxytocinase activity was similar in the two tissues. In uterine tissues, activity was greater in the cytosolic fractions. In placenta, activity was evenly distributed between the cytosolic and microsomal fractions. The cytosolic fractions of each tissue contained predominantly post-proline endopeptidase activity, whereas the microsomes contained predominantly aminopeptidase activity. There was a slight trend to decreasing oxytocinase activity with advancing gestation in both subcellular fractions, but this was statistically significant only in the microsomal fraction. The maximal decline in activity was only 25-50%. Tamoxifen treatment had no effect on oxytocinase activity. We conclude that rat uterine and placental tissues contain post-proline endopeptidase and aminopeptidase activities that metabolize OT. It is doubtful that changes in these activities are major factors in regulating the increase in OT concentrations measured in rat intrauterine tissues at the time of parturition.

Aminopeptidases↗

PubMed1997

Effects of RU486 on estrogen, progesterone, oxytocin, and their receptors in the rat uterus during late gestation.

Oxytocin (OT) and its receptor (OTR) are synthesized in the endometrium and myometrium of the pregnant rat during late gestation. Both are regulated by estrogen and progesterone (P4), and tissue concentrations of both increase markedly before parturition. The P4 antagonist RU486 will induce parturition in the rat. The purpose of the present studies was to investigate changes in OT and OTR messenger RNA (mRNA) and peptide synthesis within the pregnant rat uterus during RU486-induced parturition. Pregnant rats were given a single injection of RU486 (2.5 mg/rat in oil) on day 15 of pregnancy (normal delivery occurs on day 22). Control animals received injections of oil only. Groups of animals (n = 5 in each group) were euthanized at 0, 6, 12, 24, and 48 h after injection and during labor (immediately after delivery of the first pup). Maternal serum estradiol (E2), P4 and uterine OT, and PGE2 concentrations were measured by RIA. Prostaglandin F2alpha and estrogen receptor levels were measured by enzyme immunoassay (EIA). OTR and P4 receptor (PR) were measured using radioligand-binding assays. OT, OTR, and estrogen receptor mRNAs were measured with ribonuclease protection assays. The average time to delivery, after RU486 injection, was 27.0 +/- 1.2 h. Serum E2 and P4 levels were increased slightly, but significantly, at 24 h after RU486. In controls, OT mRNA increased significantly, and this increase was blocked in the RU486 treatment group. OTR mRNA levels increased within 6 h of RU486 and remained elevated until delivery. OTR peptide was increased by 12 h. PGE2 and PGF2alpha were increased 3-fold and 16-fold, respectively, but not until after the increase in OTR had occurred. We conclude that the mechanism of action of RU486 is to inhibit the P4 suppression of OTR synthesis, allowing increased expression of OTR, which may directly stimulate myometrial contractions or act indirectly through increased synthesis of PGs.

Animals↗

PubMed1996

The sup-pf-2 mutations of Chlamydomonas alter the activity of the outer dynein arms by modification of the gamma-dynein heavy chain.

The sup-pf-2 mutation is a member of a group of dynein regulatory mutations that are capable of restoring motility to paralyzed central pair or radial spoke defective strains. Previous work has shown that the flagellar beat frequency is reduced in sup-pf-2, but little else was known about the sup-pf-2 phenotype (Huang, B., Z. Ramanis, and D.J.L. Luck. 1982. Cell. 28:115-125; Brokaw, C.J., and D.J.L. Luck. 1985. Cell Motil. 5:195-208). We have reexamined sup-pf-2 using improved biochemical and structural techniques and by the analysis of additional sup-pf-2 alleles. We have found that the sup-pf-2 mutations are associated with defects in the outer dynein arms. Biochemical analysis of sup-pf-2-1 axonemes indicates that both axonemal ATPase activity and outer arm polypeptides are reduced by 40-50% when compared with wild type. By thin-section EM, these defects correlate with an approximately 45% loss of outer dynein arm structures. Interestingly, this loss is biased toward a subset of outer doublets, resulting in a radial asymmetry that may reflect some aspect of outer arm assembly. The defects in outer arm assembly do not appear to result from defects in either the outer doublet microtubules or the outer arm docking structures, but rather appear to result from defects in outer dynein arm components. Analysis of new sup-pf-2 mutations indicates that the severity of the outer arm assembly defects varies with different alleles. Complementation tests and linkage analysis reveal that the sup-pf-2 mutations are alleles of the PF28/ODA2 locus, which is thought to encode the gamma-dynein heavy chain subunit of the outer arm. The sup-pf-2 mutations therefore appear to alter the activity of the outer dynein arms by modification of the gamma-dynein heavy chain.

Alleles↗