The analysis of reaction norms for age and size at maturity using maturation rate models

Reaction norms for age and size at maturity are being analyzed to answer important questions about the evolution of life histories. A new statistical method is developed in the framework of time-to-event data analysis, which circumvents shortcomings in currently available approaches. The method emphasizes the estimation of age- and size-dependent maturation rates. Individual probabilities of maturation during any given time interval follow by integrating maturation rate along the growth curve. The integration may be performed in different ways, over ages or sizes or both, corresponding to different assumptions on how individuals store the operational history of the maturation process. Data analysis amounts to fitting generalized nonlinear regression models to a maturation status variable. This technique has three main advantages over existing methods: (1) treating maturation as a stochastic process enables one to specify a rate of maturation; (2) age and size at which maturation occurs do not have to be observed exactly, and bias arising from approximations and interpolations is avoided; (3) ages at which sizes are measured and maturation status are observed can differ between individuals. An application to data on the springtail Folsomia candida is presented. Models with age-dependent integration of maturation rates were preferred. The analysis demonstrates a significant size dependence of the maturation rate but no age dependence.     

Dlx5 is a positive regulator of chondrocyte differentiation during endochondral ossification

The process of endochondral ossification in which the bones of the limb are formed after generation of cartilage models is dependent on a precisely regulated program of chondrocyte maturation. Here, we show that the homeobox-containing gene Dlx5 is expressed at the onset of chondrocyte maturation during the conversion of immature proliferating chondrocytes into postmitotic hypertrophying chondrocytes, a critical step in the maturation process. Moreover, retroviral misexpression of Dlx5 during differentiation of the skeletal elements of the chick limb in vivo results in the formation of severely shortened skeletal elements that contain excessive numbers of hypertrophying chondrocytes which extend into ectopic regions, including sites normally occupied by immature chondrocytes. The expansion in the extent of hypertrophic maturation detectable histologically is accompanied by expanded and upregulated domains of expression of molecular markers of chondrocyte maturation, particularly type X collagen and osteopontin, and by expansion of mineralized cartilage matrix, which is characteristic of terminal hypertrophic differentiation. Furthermore, Dlx5 misexpression markedly reduces chondrocyte proliferation concomitant with promoting hypertrophic maturation. Taken together, these results indicate that Dlx5 is a positive regulator of chondrocyte maturation and suggest that it regulates the process at least in part by promoting conversion of immature proliferating chondrocytes into hypertrophying chondrocytes. Retroviral misexpression of Dlx5 also enhances formation of periosteal bone, which is derived from the Dlx5-expressing perichondrium that surrounds the diaphyses of the cartilage models. This suggests that Dlx5 may be involved in regulating osteoblast differentiation, as well as chondrocyte maturation, during endochondral ossification.     

Cellubrevin alterations and Mycobacterium tuberculosis phagosome maturation arrest

The intracellular trafficking processes controlling phagosomal maturation remain to be fully delineated. Mycobacterium tuberculosis var. bovis BCG, an organism that causes phagosomal maturation arrest, has emerged as a tool for dissection of critical phagosome biogenesis events. In this work, we report that cellubrevin, a v-SNARE functioning in endosomal recycling and implicated in endosomal interactions with post-Golgi compartments, plays a role in phagosomal maturation and that it is altered on mycobacterial phagosomes. Both mycobacterial phagosomes, which undergo maturation arrest, and model phagosomes containing latex beads, which follow the normal pathway of maturation into phagolysosomes, acquired cellubrevin. However, the mycobacterial and model phagosomes differed, as a discrete proteolytic degradation of this SNARE was detected on mycobacterial phagosomes. The observed cellubrevin alteration on mycobacterial phagosomes was not a passive event secondary to a maturation arrest at another checkpoint of the phagosome maturation pathway, since pharmacological inhibitors of phagosomal/endosomal pathways blocking phagosomal maturation did not cause cellubrevin degradation on model phagosomes. Cellubrevin status on phagosomes had consequences on phagosomal membrane and lumenal content trafficking, involving plasma membrane marker recycling and delivery of lysosomal enzymes. These results suggest that cellubrevin plays a role in phagosomal maturation and that it is a target for modification by mycobacteria or by infection-induced processes in the host cell.     

Effects of several inhibitors of macromolecule synthesis upon maturation of marine invertebrate oocytes

Protein, RNA and DNA syntheses, during oocyte maturation in Asterias glacialis and Chaetopterus, have been studied with cytochemical and biochemical methods. The effects of several inhibitors of the biosynthesis of these macromolecules have been investigated. The results show that protein synthesis is required for maturation: fusidic acid and puromycin, which strongly inhibit protein synthesis, prevent maturation. However, a paradoxical effect of cycloheximide was observed in Chaetopterus oocytes: this drug, like KCl, induces activation of the eggs. DNA and RNA are synthesized during maturation, but studies with inhibitors show that these syntheses are not necessary for the completion of maturation. Protein synthesis was followed during maturation and activation of Chaetopterus oocytes. It was observed that protein synthesis, which stops at the end of maturation, is not readily restored by activation. The significance of these results is discussed.     

Hormone-induced cortical maturation ensures the slow block to polyspermy and does not couple with meiotic maturation in starfish

Meiotic progression in starfish oocytes is reinitiated by a maturation-inducing hormone called 1-methyladenine (1-MeAde). In addition to meiotic maturation, 1-MeAde induces cortical maturation in which cortical granules become competent to discharge in response to fusion of a single sperm, which results in the formation of the fertilization envelope. We found that subthreshold concentrations of 1-MeAde induce cortical maturation without germinal vesicle breakdown (GVBD). During cortical maturation, the IP3 sensitivity of calcium stores was increased as well as during meiotic maturation. When oocytes were exposed with 1-MeAde only on a hemisphere of oocytes, the IP3 sensitivity of the cortical region was increased only in the exposed hemisphere, suggesting that signals and components involved in cortical maturation do not readily spread in the cytoplasm. Although a specific inhibitor of phosphatidylinositol-3 kinase, LY294002 blocked both GVBD and cortical maturation, a Cdc2 kinase inhibitor, roscovitine did not block cortical maturation. Inhibition of Akt activation by injecting the competitors for Akt phosphorylation and membrane recruitment also blocked cortical maturation. These results suggest that the signaling pathway leading to Akt activation is common in cortical maturation and meiotic maturation, and Cdc2 activation was not required for cortical maturation.     

Influence of hyaluronan accumulation during cumulus expansion on in vitro porcine oocyte maturation

During oocyte maturation, the cumulus-oocyte complexes (COCs) expand dramatically. This phenomenon, which is known as cumulus expansion, is the result of the synthesis and accumulation of hyaluronan in the extracellular space between cumulus cells. The purpose of this study was to investigate the effect of 6-diazo-5-oxo-l-norleucine (DON), an inhibitor of hyaluronan synthesis, on cumulus expansion during in vitro porcine oocyte maturation and hyaluronan accumulation within COCs. Further, this study aimed to examine the influence of hyaluronan accumulation within COCs on the rate of oocyte maturation. Cumulus expansion was observed during in vitro maturation. However, the addition of DON to the maturation medium significantly inhibited cumulus expansion. The total inhibition of hyaluronan accumulation within COCs was observed with the use of confocal microscopy. Moreover, a positive correlation between the area of cumulus expansion and the rate of oocyte maturation was observed. These results demonstrate that the hyaluronan accumulation within the COCs during oocyte maturation affects oocyte maturation. On the basis of these results, we propose that hyaluronan accumulation within the COCs during cumulus expansion is a necessary step in the porcine oocyte maturation process.     

Protein phosphorylation and oocyte maturation. I. Induction of starfish oocyte maturation by intracellular microinjection of a phosphatase inhibitor, alpha-naphthylphosphate

Oocyte maturation (meiosis re-initiation) in starfish is induced by the natural hormone 1-methyladenine (1-MeAde). Following hormonal stimulation of the oocyte, an intracellular Maturation Promoting Factor (MPF) appears in the cytoplasm which triggers nuclear envelope breakdown and maturation divisions. alpha-Naphthylphosphate (alpha-NP), a widely used phosphatase inhibitor/substrate, was found to induce oocyte maturation when microinjected intracellularly (50% maturation of 3.5 mM; 100% above 6mM, final intracellular concentration) into oocytes of Marthasterias and Asterias but not of Astropecten. As 1-MeAde, alpha-NP triggers a complete maturation, i.e. germinal vesicle breakdown, extrusion of the two polar bodies and formation of the female pronucleus. The kinetics of alpha-NP-induced maturation (35-45 min) is, however, longer than the kinetics of 1-MeAde-induced maturation (18-20 min). The addition of alpha-NP externally to oocytes does not trigger maturation. Among several reported phosphatase inhibitors, including two natural protein phosphatase inhibitors and several products structurally related to alpha-NP, only alpha-NP was found capable of inducing maturation when microinjection into oocytes. alpha-NP triggers the appearance of MPF activity in the cytoplasm of oocytes into which it has been injected. Although alpha-NP-induced maturation is insensitive to inhibitors whose action is known to be restricted to the hormone-dependent period (such as the protease inhibitor leupeptin), it is blocked by inhibitors of MPF action (such as nicotinamide and lithium). Finally it was found that alpha-NP-induced maturation is inhibited by simultaneous microinjection of protein phosphatase-2A; also, alpha-NP, classically used as an inhibitor of acid and alkaline phosphatases, is able to inhibit protein phosphatases, is able to inhibit protein phosphatases 1 and 2 A. The addition of alpha-NP to oocytes increases the level of phosphorylated proteins. These results constitute direct evidence that an elevated level of phosphorylated proteins is sufficient to trigger MPF activity and to induce maturation.     

A mathematical model for germinal centre kinetics and affinity maturation

We present a mathematical model which reproduces experimental data on the germinal centre (GC) kinetics of the primed primary immune response and on affinity maturation observed during the reaction. We show that antigen masking by antibodies which are produced by emerging plasma cells can drive affinity maturation and provide a feedback mechanism by which the reaction is stable against variations in the initial antigen amount over several orders of magnitude. This provides a possible answer to the long-standing question of the role of antigen reduction in driving affinity maturation. By comparing model predictions with experimental results, we propose that the selection probability of centrocytes and the recycling probability of selected centrocytes are not constant but vary during the GC reaction with respect to time. It is shown that the efficiency of affinity maturation is highest if clones with an affinity for the antigen well above the average affinity in the GC leave the GC for either the memory or plasma cell pool. It is further shown that termination of somatic hypermutation several days before the end of the germinal centre reaction is beneficial for affinity maturation. The impact on affinity maturation of simultaneous initiation of memory cell formation and somatic hypermutation vs. delayed initiation of memory cell formation is discussed.     

卵丘在卵母细胞成熟中的作用

卵丘是指在卵母细胞外周并与之进行代谢联系的颗粒细胞群;卵丘对于卵母细胞成熟有极其重要的作用。主要表现在卵丘参与维持卵母细胞减数分裂阻滞,诱导卵母细胞减数分裂恢复、支持卵母细胞细胞质的成熟。卵丘形态和卵丘扩展影响卵母细胞成熟。了解卵丘在卵母细胞成熟中的作用有助于帮助人们进一步揭示哺乳动物卵母细胞成熟的机制。     

Phagosome maturation: going through the acid test

Phagosome maturation is the process by which internalized particles (such as bacteria and apoptotic cells) are trafficked into a series of increasingly acidified membrane-bound structures, leading to particle degradation. The characterization of the phagosomal proteome and studies in model organisms and mammals have led to the identification of numerous candidate proteins that cooperate to control the maturation of phagosomes containing different particles. A subset of these candidate proteins makes up the first pathway to be identified for the maturation of apoptotic cell-containing phagosomes. This suggests that a machinery that is distinct from receptor-mediated endocytosis is used in phagosome maturation.     

Importance of the CEP215-Pericentrin Interaction for Centrosome Maturation during Mitosis

At the onset of mitosis, the centrosome undergoes maturation, which is characterized by a drastic expansion of the pericentriolar material (PCM) and a robust increase in microtubule-organizing activity. CEP215 is one of the major PCM components which accumulates at the centrosome during mitosis. The depletion phenotypes indicate that CEP215 is essential for centrosome maturation and bipolar spindle formation. Here, we performed a series of knockdown-rescue experiments to link the protein-protein interaction properties of CEP215 to its biological functions. The results showed that CEP215 and pericentrin, another major PCM component, is interdependent for their accumulation at the spindle poles during mitosis. As a result, The CEP215-pericentrin interaction is required for centrosome maturation and subsequent bipolar spindle formation during mitosis. On the other hand, CEP215 interaction with γ-tubulin is dispensable for centrosome maturation. Our results provide an insight how PCM components are assembled to form a spindle pole during mitosis.     

线粒体与卵母细胞发育

卵子发育、成熟是一个复杂的过程, 细胞核成熟和细胞质成熟过程必须同步化, 才能保证卵子的正常受精和进一步的发育。作为细胞质内最重要的细胞器, 线粒体在卵子成熟过程中的分布的变化、氧化磷酸化产生ATP的能力以及线粒体ＤＮＡ的含量和拷贝数或转录水平对卵母细胞发育成熟有着重要的影响。因此, 对卵子成熟过程中线粒体的分布和功能状况及线粒体DNA的研究, 有利于进一步了解生殖生理, 并为解决辅助生殖技术中及克隆胚胎技术所面临的困难提供新的思路。     

A quantitative analysis of the human bone marrow erythroblastic cell lineage using the SAMBA 200 cell image processor. I. The normal maturation sequence

A quantitative image analysis of the normal maturation sequence for the human bone marrow erythroblastic lineage was performed using the SAMBA 200 cell image processor. The different image analysis steps (image acquisition, preprocessing, segmentation, parametrization and data analysis) are briefly described. Thirty-three parameters related to geometry, color, texture and densitometry were computed on 638 cell images belonging to the five erythroblastic maturation stages. The automated classification of these cells, based upon a stepwise linear discriminant analysis, resulted in 80% correctly classified cells. Acceptance of confusions between successive maturation stages enhanced the rate of correctly classified cells to 100%. Among the ten most discriminating parameters, the nuclear area showed the highest correlation with the changes throughout the maturation process. The projection of the maturation sequence onto the factorial plane resulting from the canonical analysis emphasizes the existence of three phases of the maturation process, a finding that correlates well with the cytologic evolution and the biochemical and functional events during the maturation. The trajectory of cells within this factorial plane is thus regarded as a differentiation path from which a measure of the maturation could be derived.     

The role of calcium in the nuclear maturation of Bufo arenarum oocytes

In Bufo arenarum, progesterone is the physiological maturation inducer. However, in this species, oocytes reinitiate meiosis with no need of an exogenous hormonal stimulus when deprived of their enveloping cell, a phenomenon called spontaneous maturation. We demonstrated that in Bufo arenarum spontaneous maturation occurs only in oocytes obtained during the reproductive period, which can be considered competent to mature spontaneously, in contrast to those in the non-reproductive period, which are incompetent. Interestingly, full-grown Bufo arenarum oocytes always respond to progesterone regardless of the season in which they are obtained. There is a general consensus that both a transient increase in intracellular calcium and a decrease in cAMP-dependent protein kinase activity are the first steps in the mechanisms by which progesterone induces maturation in amphibians. In the present work we analysed the role of calcium in the spontaneous and progesterone-induced maturation of Bufo arenarum oocytes. Results demonstrated that the absence of calcium in the incubation medium or the prevention of Ca(2+) influx by channel blockers such as CdCl2 or NiCl2 did not prevent meiosis reinitiation in either type of maturation. The inhibition of the Ca(2+)-calmodulin complex in no case affected the maturation of the treated oocytes. However, when the oocytes were deprived of calcium by incubation in Ca(2+)-free AR + A23187, meiosis resumption was inhibited. In brief, we demonstrated that in Bufo arenarum the reinitiation of meiosis is a process independent of extracellular calcium at any period of the year and that oocytes require adequate levels of intracellular calcium for germinal vesicle breakdown to occur.     

Harvest-induced maturation evolution under different life-history trade-offs and harvesting regimes

The potential of harvesting to induce adaptive changes in exploited populations is now increasingly recognized. While early studies predicted that elevated mortalities among larger individuals select for reduced maturation size, recent theoretical studies have shown conditions under which other, more complex evolutionary responses to size-selective mortality are expected. These new predictions are based on the assumption that, owing to the trade-off between growth and reproduction, early maturation implies reduced growth. Here we extend these findings by analyzing a model of a harvested size-structured population in continuous time, and by systematically exploring maturation evolution under all three traditionally acknowledged costs of early maturation: reduced fecundity, reduced growth, and/or increased natural mortality. We further extend this analysis to the two main types of harvest selectivity, with an individual's chance of getting harvested depending on its size and/or maturity stage. Surprisingly, we find that harvesting mature individuals not only favors late maturation when the costs of early maturation are low, but promotes early maturation when the costs of early maturation are high. To our knowledge, this study therefore is the first to show that harvesting mature individuals can induce early maturation.