RESUMEN
Vertical migration as well as horizontal dispersion is important in the ecological strategy of planktonic larvae of sedentary corals. We report in this paper unique vertical swimming behavior of planulae of the reef-building coral Acropora tenuis. Several days after fertilization, most of the planulae stayed exclusively at either the top or the bottom of the rearing tank. A good proportion of the planulae migrated almost vertically between top and bottom with fairly straight trajectories. Planulae sometimes switched their swimming direction via a sharp turn between the opposite directions. Quantitative analyses demonstrated that planulae kept constant speed while swimming either upward or downward, in contrast to frequent changes of direction and speed in horizontal swimming. Statistical comparison of propulsive speeds, estimated from swimming speeds and passive sedimentation, revealed gravikinesis of planulae, where the propulsive speed was significantly greater in downward swimming than upward swimming. The larval density hydrodynamically estimated was 0.25% lower than sea water density, which might be explained by the large quantity of lipids in planulae. Also, the deciliated larvae tended to orient oral end-up during floatation, presumably due to asymmetrical distribution of the endogenous light lipids. Plasticity of the larval tissue geometry could easily cause relocation of the center of forces which work together to generate gravitactic-orientation torque and, therefore, abrupt changing of the gravitactic swimming direction. The bimodal gravitactic behavior may give a new insight into dispersal and recruitment of coral larvae.
Asunto(s)
Antozoos , Animales , Larva , Natación , Agua de Mar , LípidosRESUMEN
In Phlebobranchiata ascidians, oocytes and spermatozoa are stored in the oviduct and spermiduct, respectively, until spawning occurs. Gametes in the gonoducts are mature and fertilizable; however, it was found that the gametes of the ascidians Phallusia philippinensis and Ciona intestinalis could not undergo fertilization in the gonoductal fluids. The body fluids of the ascidians, especially in the gonoducts, were much more acidic (pH 5.5-6.8) than seawater (pH 8.2), and the fertilization rate was low under such acidic conditions. Hence, we examined the effect of pH on gametes. Pre-incubation of gonoductal eggs at pH 8.2 prior to insemination increased fertilization rates, even when insemination was performed under low pH conditions. Furthermore, an increase in ambient pH induced an increase in the intracellular pH of the eggs. It was also found that an increase in ambient pH triggered the release of sperm attractants from the egg and is therefore necessary for sperm chemotaxis. Hence, acidic conditions in the gonoductal fluids keep the gametes, especially eggs, infertile, and the release of eggs into seawater upon spawning induces an increase in ambient pH, which enables egg fertilization.
Asunto(s)
Ciona intestinalis , Fertilización , Animales , Masculino , Fertilización/fisiología , Semen , Espermatozoides/fisiología , Concentración de Iones de HidrógenoRESUMEN
OBJECTIVES: This study aimed to clarify the relationship between vitamin D status and complications after periacetabular osteotomy. METHODS: A total of 46 hips of 39 patients (3 men and 36 women; mean age at surgery, 41.0 years; mean postoperative follow-up duration, 63 months) were reviewed to obtain the following information: patients' serum 25-hydroxyvitamin D [25(OH)D] status, prevalence of postoperative delayed union of osteotomy sites in the greater trochanter (DUGT) and ischiopubic stress fractures (IPSFs), and risk factors. RESULTS: The mean serum 25(OH)D level was 11.9 ng/ml. DUGT and IPSF were found in four (10.3%) and three (7.7%) patients, respectively. Serum 25(OH)D levels ≤ 11 ng/ml were significantly associated with DUGT in female patients (p = .02). Serum 25(OH)D levels ≤ 9 ng/ml and smoking were significantly associated with IPSF (p = 0.01 and 0.02, respectively). Overall, 21.7% of patients with serum 25(OH)D levels ≤ 11 ng/ml developed at least one complication; no complications occurred when serum 25(OH)D levels were >11 ng/ml. CONCLUSION: Severe vitamin D deficiency was highly prevalent in relatively young patients. Vitamin D deficiency and smoking were independent risk factors for postoperative complications. Proactive supplementation is advisable to reduce postoperative complications, especially in patients with serum 25(OH)D levels ≤ 11 ng/ml.
Asunto(s)
Luxación Congénita de la Cadera , Luxación de la Cadera , Deficiencia de Vitamina D , Masculino , Humanos , Femenino , Adulto , Estudios de Casos y Controles , Luxación de la Cadera/complicaciones , Vitamina D , Luxación Congénita de la Cadera/complicaciones , Vitaminas , Osteotomía/efectos adversos , Complicaciones Posoperatorias/etiologíaRESUMEN
OBJECTIVES: This study aimed to report the mid-term radiological outcomes of patients with bipolar hemiarthroplasty (BHA) for stage 3 osteonecrosis of the femoral head (ONFH), and to identify the risk factors for postoperative radiological changes. METHODS: We retrospectively investigated 62 patients (38 men and 24 women; mean age, 50.1 years) aged <70 years who underwent primary BHA for Association Research Circulation Osseous stage 3 ONFH between 1998 and 2010. The mean follow-up period after BHA was 12.8 years. The following changes were assessed on follow-up radiographs: outer head migration, polyethylene wear, and femoral osteolysis. The association between demographic data and the development of postoperative radiological changes was evaluated. RESULTS: Radiological changes were found in 20 hips (32.3%) at a mean of 8.1 years after BHA; of these, three hips (4.8%) underwent total hip arthroplasty conversion at a mean of 10.9 years after BHA. Both univariate and multivariate analysis revealed that younger age and female sex were independent risk factors for the development of postoperative radiological changes. CONCLUSION: The current results suggest that the indication of BHA should be carefully determined in young or female patients with ONFH, even when the disease is in the early stage.
Asunto(s)
Necrosis de la Cabeza Femoral/cirugía , Hemiartroplastia/efectos adversos , Complicaciones Posoperatorias/epidemiología , Adulto , Anciano , Artroplastia de Reemplazo de Cadera/normas , Femenino , Cabeza Femoral/diagnóstico por imagen , Cabeza Femoral/cirugía , Hemiartroplastia/métodos , Humanos , Masculino , Persona de Mediana Edad , Complicaciones Posoperatorias/diagnóstico por imagen , Complicaciones Posoperatorias/cirugíaRESUMEN
OBJECTIVE: To evaluate the relationship between the volume of hip synovitis detected on contrast-enhanced magnetic resonance imaging (MRI) and the disease stage of osteonecrosis of the femoral head (ONFH). MATERIALS AND METHODS: Sixty-three consecutive hips in 40 ONFH patients were reviewed using contrast-enhanced MRI. Ten unaffected hips in 10 patients with unilateral ONFH were used as controls. Based on the Japanese Investigation Committee system, these hips were classified according to stage and type. The volume and location of hip synovitis were semi-quantitatively measured on contrast-enhanced MRI. Clinicoradiological factors were statistically analyzed to determine the relationship with the volume of hip synovitis. RESULTS: The mean synovial volume was significantly larger in ONFH hips (8,020 ± 6,900 mm3) than in controls (910 ± 1,320 mm3; p = 0.001). The area of synovitis in the anterior portion of the hip joint was double (mean: 2.17 ± 1.77) that in the posterior portion. The volume of synovitis was small in pre-collapse-stage hips (stage 1: 680 ± 690 mm3, stage 2: 1,460 ± 1,200 mm3), but significantly larger in post-collapse-stage hips (stage 3A: 7,820 ± 4,490 mm3, stage 3B: 13,850 ± 7,110 mm3; p < 0.001). Multiple regression analysis showed that disease stage was the only factor related to hip synovitis. CONCLUSIONS: Our study suggests that hip synovitis in ONFH might occur after femoral head collapse and worsen with collapse progression, mainly in the anterior portion.
Asunto(s)
Necrosis de la Cabeza Femoral/complicaciones , Necrosis de la Cabeza Femoral/diagnóstico por imagen , Articulación de la Cadera , Sinovitis/diagnóstico por imagen , Sinovitis/etiología , Adulto , Estudios de Casos y Controles , Femenino , Humanos , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Índice de Severidad de la Enfermedad , Sinovitis/patología , Adulto JovenRESUMEN
PURPOSE: The location of the necrotic lesion is one of the important factors for collapse in osteonecrosis of the femoral head (ONFH). The significance of anterior localization has been little studied. This study evaluated the effects of anterior boundary of a necrotic lesion on collapse. METHODS: We reviewed the outcomes of 113 consecutive non-collapsed asymptomatic hips in 98 ONFH patients with mean follow-up of 4.7 years (2.0-11.8) after the initial magnetic resonance (MR) imaging. The presence or absence of collapse was investigated using follow-up radiographs. The location of the anterior boundary of a necrotic lesion was assessed using the anterior necrotic angle between the midline of the femoral neck shaft and the line passing from the femoral head centre to the anterior boundary on mid-oblique MR imaging. Multivariate analysis was performed to identify risk factors for collapse, and further analyses were executed according to the lateral boundary of the necrotic lesion. RESULTS: During the follow-up period, collapse was confirmed in 61 hips (54.0%). Multivariate analysis revealed that the anterior necrotic angle was independently associated with collapse as well as the lateral boundary of the necrotic lesion. When the lateral boundary was located at the middle third of weight-bearing portion (32 hips), that was generally categorized as a low risk of collapse, all five cases with anterior necrotic angle ≥ 79° developed collapse, whereas only one of 27 cases (3.7%) with an anterior necrotic angle < 79° developed collapse (p < 0.0001). CONCLUSIONS: This study indicates that ONFH patients with anterior localization of a necrotic lesion can develop collapse even if the necrotic lesion is medially located.
Asunto(s)
Necrosis de la Cabeza Femoral/complicaciones , Cabeza Femoral/patología , Articulación de la Cadera/patología , Adulto , Anciano , Femenino , Cabeza Femoral/diagnóstico por imagen , Estudios de Seguimiento , Articulación de la Cadera/diagnóstico por imagen , Humanos , Imagen por Resonancia Magnética/métodos , Masculino , Persona de Mediana Edad , Estudios Retrospectivos , Factores de Riesgo , Análisis de SupervivenciaRESUMEN
Thermotaxis that sperm migrate to higher temperature area has been confirmed in rabbit and human. In this study, we examined the migration ability of bull sperm in a temperature gradient to confirm thermotaxis and elucidate the involvement of calcium in such thermotaxis, as well as the relation between sperm capacitation and bull fertility. Thermotaxis was evaluated in a temperature gradient of 34-42ºC using a cross-type column 22-mm long, 40-mm wide, and 100-µm deep. Significantly more sperm migrated to the high-temperature area of 39ºC in a 2ºC temperature gradient, and to 40ºC in a 1ºC temperature gradient. In calcium-free, BAPTA containing medium, and EGTA containing medium, the migrated sperm ratio in the two temperature areas was almost the same. In media containing lanthanum, ruthenium red, and 2APB, we could not confirm thermotaxis. Pre- and post-capacitated sperm migrated to the high-temperature area, expressing thermotaxis. The sperm from high-fertility bulls showed clear thermotaxis. Based on these results, thermotaxis of bull sperm was confirmed and the involvement of both calcium channels and intracellular stored calcium in thermotaxis was suggested. Although the sample size of bulls was quite small, the difference in thermotaxis may have been associated with bull fertility. Sperm thermotaxis evaluation has potential as a predictor of bull fertility.
Asunto(s)
Canales de Calcio/metabolismo , Calcio/metabolismo , Espermatozoides/metabolismo , Taxia/fisiología , Animales , Bovinos , Masculino , Capacitación Espermática/fisiología , Motilidad Espermática/fisiología , Espermatozoides/citología , TemperaturaRESUMEN
A 23-year-old Japanese woman with no history of corticosteroid intake or alcohol abuse presented with a 10-month history of left hip pain without any antecedent trauma. An anteroposterior radiograph performed 10 months after the onset of pain showed slight joint space narrowing and bone erosions surrounded by sclerotic lesions in both the acetabular roof and femoral neck. Magnetic resonance images of the left hip showed a feature of osteonecrosis of the femoral head and a mass with villus proliferation extending from the posterior intertrochanteric area to the anteromedial aspect of the femoral neck. In addition, the left quadratus femoris muscle, which is generally located just above the nutrient vessels of the femoral head, was not detected. Based on these findings, the patient was diagnosed with osteonecrosis of the femoral head caused by impairment of the nutrient vessels from invasion of the pigmented villonodular synovitis. She underwent radical synovectomy of the left hip 16 months after the onset of pain, and her hip pain improved after the surgery.
Asunto(s)
Necrosis de la Cabeza Femoral/complicaciones , Sinovitis Pigmentada Vellonodular/complicaciones , Femenino , Cabeza Femoral/diagnóstico por imagen , Cabeza Femoral/patología , Necrosis de la Cabeza Femoral/diagnóstico por imagen , Necrosis de la Cabeza Femoral/patología , Humanos , Imagen por Resonancia Magnética , Sinovitis Pigmentada Vellonodular/diagnóstico por imagen , Sinovitis Pigmentada Vellonodular/patología , Adulto JovenRESUMEN
Aim: To examine the potential of bovine follicular fluid (BFF) to attract bull spermatozoa. Methods: The ability of the BFF to attract bull sperm was evaluated by observing changes in sperm migration after being placed in a cross-column chamber. The movement parameters of the heads and flagella of the sperm that were attracted to the BFF were analyzed by using the Computer Assisted Sperm Analysis system. Results: It was observed that 61.6% of the bull sperm migrated toward the BFF when the BFF was used at a concentration of 0.1%, but 67.2% of the sperm did not migrate toward the BFF at a concentration of 10%. Relatively larger numbers of both precapacitated and postcapacitated bull sperm migrated toward the BFF (0.1%). The ability of the 0.1% BFF to attract sperm probably affected both the normal artificial insemination (AI) fertility sperm and the poor AI fertility spermatozoa. The flagellar curvilinear ratio of the sperm winding to the 0.1% BFF was significantly higher than that of the prewinding sperm. Conclusion: These results could suggest that BFF potentially attracts bull sperm at a certain concentration, irrespective of the capacitation status of the sperm. Although the mechanism by which this attraction occurs remains unclear, these data imply that it could be related to BFF-dependent changes in the sperm flagellar curvilinear ratio.
RESUMEN
A hallmark of neurogenesis in the vertebrate brain is the apical-basal nuclear oscillation in polarized neural progenitor cells. Known as interkinetic nuclear migration (INM), these movements are synchronized with the cell cycle such that nuclei move basally during G1-phase and apically during G2-phase. However, it is unknown how the direction of movement and the cell cycle are tightly coupled. Here, we show that INM proceeds through the cell cycle-dependent linkage of cell-autonomous and non-autonomous mechanisms. During S to G2 progression, the microtubule-associated protein Tpx2 redistributes from the nucleus to the apical process, and promotes nuclear migration during G2-phase by altering microtubule organization. Thus, Tpx2 links cell-cycle progression and autonomous apical nuclear migration. In contrast, in vivo observations of implanted microbeads, acute S-phase arrest of surrounding cells and computational modelling suggest that the basal migration of G1-phase nuclei depends on a displacement effect by G2-phase nuclei migrating apically. Our model for INM explains how the dynamics of neural progenitors harmonize their extensive proliferation with the epithelial architecture in the developing brain.
Asunto(s)
Encéfalo/embriología , Ciclo Celular/fisiología , Núcleo Celular/fisiología , Proteínas Asociadas a Microtúbulos/metabolismo , Microtúbulos/fisiología , Modelos Moleculares , Células-Madre Neurales/fisiología , Neurogénesis/fisiología , Animales , Polaridad Celular/fisiología , Proliferación Celular , Cartilla de ADN/genética , Técnicas de Silenciamiento del Gen , Ratones , Microscopía Fluorescente , Microesferas , Transporte de Proteínas/fisiología , Interferencia de ARN , Imagen de Lapso de TiempoAsunto(s)
Cabeza Femoral/lesiones , Fracturas por Estrés/diagnóstico , Fracturas por Estrés/etiología , Fracturas de Cadera/diagnóstico , Fracturas de Cadera/etiología , Osteoartritis de la Cadera/complicaciones , Anciano , Femenino , Fracturas por Estrés/terapia , Fracturas de Cadera/terapia , HumanosAsunto(s)
Epífisis/lesiones , Epífisis/cirugía , Fracturas del Fémur/cirugía , Cabeza Femoral/cirugía , Fracturas por Estrés/cirugía , Osteoartritis de la Cadera/cirugía , Artroplastia de Reemplazo de Cadera , Epífisis/diagnóstico por imagen , Femenino , Fracturas del Fémur/diagnóstico por imagen , Cabeza Femoral/diagnóstico por imagen , Fracturas por Estrés/diagnóstico por imagen , Humanos , Persona de Mediana Edad , Osteoartritis de la Cadera/diagnóstico por imagenRESUMEN
The larva of the invertebrate chordate Ciona intestinalis possesses only 36 striated muscle cells and lacks body segmentation. It can swim, however, like a vertebrate tadpole, and how its simple body achieves such sophisticated motor control remains puzzling. We found that muscle contractions in Ciona larvae are variable and can be changed by sensory stimuli, so that neuromuscular transmission can convert the variable neural inputs into graded muscle activity. We characterized the molecular nature of the nicotinic acetylcholine receptor (nAChR) at neuromuscular synapses. When heterologously expressed in Xenopus oocytes, this nAChR channel exhibited two biophysical features resembling vertebrate neuronal nAChRs rather than the muscle type: inward rectification and high Ca(2+) permeability. Both of these properties were abolished by a simple mutation at the channel pore in one of the non-α subunits, called BGDE3, so as to adopt the sequence of related subunits in vertebrates, γ and ε. In vivo exchange of native BGDE3 with this mutant severely disrupted graded motor control, producing instead sporadic all-or-none-like flexions. The graded nature of excitation-contraction (E-C) coupling in this organism is based on the traits of the nAChR channel pore, which confer fine controllability on such a coarse motor architecture.
Asunto(s)
Ciona intestinalis/metabolismo , Músculos/metabolismo , Conducción Nerviosa/fisiología , Unión Neuromuscular/metabolismo , Receptores Colinérgicos/metabolismo , Animales , Secuencia de Bases , Ciona intestinalis/genética , Expresión Génica , Larva/genética , Larva/metabolismo , Datos de Secuencia Molecular , Contracción Muscular/fisiología , Músculos/inervación , Unión Neuromuscular/genética , Oocitos , Subunidades de Proteína/genética , Subunidades de Proteína/metabolismo , Receptores Colinérgicos/genética , Xenopus laevisRESUMEN
To fuse with oocytes, spermatozoa of eutherian mammals must pass through extracellular coats, the cumulus cell layer, and the zona pellucida (ZP). It is generally believed that the acrosome reaction (AR) of spermatozoa, essential for zona penetration and fusion with oocytes, is triggered by sperm contact with the zona pellucida. Therefore, in most previous studies of sperm-oocyte interactions in the mouse, the cumulus has been removed before insemination to facilitate the examination of sperm-zona interactions. We used transgenic mouse spermatozoa, which enabled us to detect the onset of the acrosome reaction using fluorescence microscopy. We found that the spermatozoa that began the acrosome reaction before reaching the zona were able to penetrate the zona and fused with the oocyte's plasma membrane. In fact, most fertilizing spermatozoa underwent the acrosome reaction before reaching the zona pellucida of cumulus-enclosed oocytes, at least under the experimental conditions we used. The incidence of in vitro fertilization of cumulus-free oocytes was increased by coincubating oocytes with cumulus cells, suggesting an important role for cumulus cells and their matrix in natural fertilization.
Asunto(s)
Reacción Acrosómica/fisiología , Células del Cúmulo/fisiología , Fertilización In Vitro , Oocitos/fisiología , Espermatozoides/fisiología , Zona Pelúcida/fisiología , Animales , Técnicas de Cocultivo , Células del Cúmulo/citología , Femenino , Humanos , Masculino , Ratones , Ratones Noqueados , Microscopía Fluorescente , Oocitos/citología , Espermatozoides/citologíaRESUMEN
Eukaryotic flagella collectively form metachronal waves that facilitate the ability to cause flow or swim. Among such flagellated and planktonic swimmers, large volvocine genera such as Eudorina, Pleodorina and Volvox form bundles of small male gametes (sperm) called "sperm packets" for sexual reproduction. Although these sperm packets reportedly have flagella and the ability to swim, previous studies on volvocine motility have focused on asexual forms and the swimming characteristics of sperm packets remain unknown. However, it is important to quantify the motility of sperm packets and sperm in order to gain insights into the significance of motility in the sexual reproduction of planktonic algae. In this study, we quantitatively described the behavior of three flagellated forms of a male strain of Pleodorina starrii-asexual colonies, sperm packets, and single dissociated sperm-with emphasis on comparison of the two multicellular forms. Despite being smaller, sperm packets swam approximately 1.4 times faster than the asexual colonies of the same male strain. Body length was approximately 0.5 times smaller in the sperm packets than in asexual colonies. The flagella from sperm packets and asexual colonies showed asymmetric waveforms, whereas those from dissociated single sperm showed symmetric waveforms, suggesting the presence of a switching mechanism between sperm packets and dissociated sperm. Flagella from sperm packets were approximately 0.5 times shorter and had a beat period approximately twice as long as those from asexual colonies. The flagella of sperm packets were densely distributed over the anterior part of the body, whereas the flagella of asexual colonies were sparse and evenly distributed. The distribution of flagella, but not the number of flagella, appear to illustrate a significant difference in the speeds of sperm packets and asexual colonies. Our findings reveal novel aspects of the regulation of eukaryotic flagella and shed light on the role of flagellar motility in sexual reproduction of planktonic algae.
Asunto(s)
Chlorophyta , Flagelos , Chlorophyta/fisiología , Flagelos/fisiología , Motilidad Espermática/fisiología , Espermatozoides/fisiologíaRESUMEN
BACKGROUND: The incidence of developmental dysplasia of the hip (DDH) in Japanese newborns has reduced drastically following a primary prevention campaign initiated around 1972 to 1973; this perinatal education campaign promoted maintaining the hips of newborns in the naturally flexed-leg position. The purpose of the present study was to describe the life course epidemiology of hip osteoarthritis (OA) in adolescent and adult patients and to assess its association with exposure to the primary prevention campaign for DDH. METHODS: We included new patients with hip OA diagnosed from January 1, 2022, to December 31, 2022, at 12 core hospitals (8 special-function hospitals and 4 regional medical care support hospitals). The trend in the percentage of hips with a history of DDH treatment in childhood was estimated with use of a centered moving average using the birth year of the patient. We compared the prevalence of severe subluxation (Crowe type II, III, or IV) between patients with secondary hip OA due to hip dysplasia who were born in or before 1972 and those who were born in or after 1973. RESULTS: Overall, 1,095 patients (1,381 hips) were included. The mean age at the time of the survey was 63.5 years (range, 15 to 95 years). A total of 795 patients (1,019 hips; 73.8% of hips) were diagnosed with secondary OA due to hip dysplasia. Approximately 13% to 15% of hips among patients born from 1963 to 1972 had a history of DDH treatment in childhood; however, the percentage decreased among patients born in or after 1973. The prevalence of severe subluxation (Crowe type II, III, or IV) among patients born in or after 1973 was 2.4%, which was significantly less than that among patients born in or before 1972 (11.1%; odds ratio, 0.20; p < 0.001). CONCLUSIONS: As of 2022, secondary hip OA due to hip dysplasia is still responsible for most new cases of adolescent and adult hip OA seen in core hospitals in Japan. However, the perinatal education campaign initiated 50 years ago, which utilized a population approach and advocated for maintaining the hips of newborns in the naturally flexed-leg position, may have improved the environmental factors of DDH, as indicated by the apparently reduced need for treatment of DDH in childhood and the associated severe subluxation. This may result in a reduced need for challenging hip surgery later in life. LEVEL OF EVIDENCE: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.
Asunto(s)
Osteoartritis de la Cadera , Humanos , Japón/epidemiología , Osteoartritis de la Cadera/epidemiología , Osteoartritis de la Cadera/etiología , Estudios Transversales , Femenino , Masculino , Anciano , Adolescente , Persona de Mediana Edad , Adulto , Anciano de 80 o más Años , Adulto Joven , Prevalencia , Displasia del Desarrollo de la Cadera/epidemiología , Luxación Congénita de la Cadera/epidemiología , Luxación Congénita de la Cadera/terapia , IncidenciaRESUMEN
Motile aquatic microorganisms are known to self-organize into bioconvection patterns. The swimming activity of a population of microorganisms leads to the emergence of macroscopic patterns of density under the influence of gravity. Although long-term development of the bioconvection pattern is important in order to elucidate the possible integration of physiological functions of individuals through bioconvection pattern formation, little quantitative investigation has been carried out. In the present paper, we present the first quantitative description of long-term behavior of bioconvection of Chlamydomonas reinhardtii, particularly focusing on the 'pattern transition response'. The pattern transition response is a sudden breakdown of the steady bioconvection pattern followed by re-formation of the pattern with a decreased wavelength. We found three phases in the pattern formation of the bioconvection of C. reinhardtii: onset, steady-state 1 (before the transition) and steady-state 2 (after the transition). In onset, the wavelength of the bioconvection pattern increases with increasing depth, but not in steady-states 1 or 2. By means of the newly developed two-axis view method, we revealed that the population of C. reinhardtii moves toward the bottom of the experimental chamber just before the pattern transition. This indicates that the pattern transition response could be caused by enhancement of the gyrotaxis of C. reinhardtii as a result of the changes in the balance between the gravitactic and gyrotactic torques. We also found that the bioconvection pattern changes in response to the intensity of red-light illumination, to which C. reinhardtii is phototactically insensitive. These facts suggest that the bioconvection pattern has a potential to drastically reorganize its convection structure in response to the physiological processes under the influence of environmental cues.
Asunto(s)
Chlamydomonas/fisiología , Convección , Gravitación , Sensación de Gravedad , Luz , Modelos Biológicos , NataciónRESUMEN
Regulation of waveform asymmetry in flagella is critical for changes in direction when sperm are swimming, as seen during the chemotaxis of sperm towards eggs. Ca2+ is an important regulator of asymmetry in flagellar waveforms. A calcium sensor protein, calaxin, is associated with the outer arm dynein and plays a key role in the regulation of flagellar motility in a Ca2+-dependent manner. However, the underlying mechanism of regulating asymmetric waves by means of Ca2+ and calaxin remains unclear. To clarify the calaxin-dependent mechanism for generating Ca2+-dependent asymmetric flagellar waveforms, we analyzed the initial step of flagellar bend formation and propagation in the sperm of the ascidian Ciona intestinalis. Our experiment used demembranated sperm cells, which were then reactivated by UV flash photolysis of caged ATP under both high and low Ca2+ concentrations. Here, we show that initial bends in the flagella are formed at the base of the sperm and propagate towards the tip during waveform generation. However, the direction of the initial bend differed between asymmetric and symmetric waves. When a calaxin inhibitor (repaglinide) was applied, it resulted in the failure of asymmetric wave formation and propagation. This was because repaglinide had no effect on initial bend formation, but it significantly inhibited the generation of the subsequent bend in the reverse direction. Switching of dynein sliding activity by mechanical feedback is crucial for flagellar oscillation. Our results suggest that the Ca2+/calaxin mechanism plays an important role in the switching of dynein activity from microtubule sliding in the principal bend into the suppressed sliding in the reverse bend, thereby allowing the sperm to successfully change direction.
RESUMEN
Eukaryotic flagella and cilia have attracted the attention of many researchers over the last century, since they are highly arranged organelles and show sophisticated bending movements. Two important cytoskeletal and motor proteins, tubulin and dynein, were first found and described in flagella and cilia. Half a century has passed since the discovery of these two proteins, and much information has been accumulated on their molecular structures and their roles in the mechanism of microtubule sliding, as well as on the architecture, the mechanism of bending movement and the regulation and signal transduction in flagella and cilia. Historical background and the recent advance in this field are described.