Role of transforming growth factor-beta in chondrogenic pattern formation in the embryonic limb: stimulation of mesenchymal condensation and fibronectin gene expression by exogenenous TGF-beta and evidence for endogenous TGF-beta-like activity

The possible role of TGF-beta-like molecules in skeletal pattern formation in the embryonic vertebrate limb was studied by analyzing the mechanism of enhancement of chondrogenesis in chick wing bud mesenchyme in vitro and testing for the presence and distribution of endogenous TGF-beta-like activity in this tissue. Transient exposure (3-6 hr) to TGF-beta 1 (1-2 ng/ml) on the day after plating resulted in a 1.5- to 2-fold enhancement of accumulation of Alcian blue (pH 1.0)-stainable extracellular matrix 5 days later. The enhancement of differentiation was preceded by an acceleration and an increase in the extent of precartilage condensation formation, visualized by Hoffman Modulation Contrast microscopy a day after TGF-beta treatment. In contrast, neither condensation nor subsequent chondrogenesis was stimulated by transient treatment with TGF-beta 1 on the day of plating. The effectiveness of a TGF-beta treatment regimen in enhancing chondrogenesis was correlated with its effectiveness in stimulating condensation formation. Exposures to the factor for 3-6 hr on the day after plating, which most consistently stimulated both condensation formation and chondrogenesis, also corresponded to a peak in the enhancement of the steady-state level of fibronectin mRNA (fourfold to eightfold over control levels) measured at the end of the treatment period. The elevation in fibronectin mRNA levels brought about by this treatment persisted throughout the period of condensation. Endogenous TGF-beta-like activity was detected in limb mesenchyme: extracts of freshly isolated and cultured limb tissues contained 6-25 pg TGF-beta-like activity per 1 x 10(6) cells by the Mv1Lu cell proliferation inhibition assay, and indirect immunofluorescence using a polyclonal antibody directed against a TGF-beta-related peptide indicated a patchy distribution of endogenous TGF-beta-like reactivity within a day after culture. These findings are discussed in relation to the "fibronectin prepattern" hypothesis for limb pattern formation.     

变豆菜属分类、起源与进化研究进展

变豆菜属(Sanicula)是典型的东亚-北美间断分布属,属于北极-第三纪古老区系成分。目前全世界有40种,中国(17种,11个特有种)和美国(22种,13个特有种)是2个分布中心。近年来有关变豆菜属分子系统发育研究表明该属并非单系,不同学者采用了不同的属下分类标准,但属下分类系统和种间界限仍存在争议,特别是药用植物的种类较易混淆。变豆菜属的系统进化研究主要集中在北美Sanicora DC.组及夏威夷Sandwicensis Shan and Constance组的类群,缺少对中国特有种的研究,因此该属的系统位置、起源地、迁移、扩散模式和种间进化关系均不清楚。本文对变豆菜属的分类系统、分类方法、起源和进化的研究进展进行了综述,并提出存在的问题和解决方法。     

Primary dormancy in tomato (Lycopersicon esculentum cv. Moneymaker): studies with the sitiens mutant

Intact wild-type tomato (Lycopersicon esculentum cv. Moneymaker)seeds do not complete germination to the same percentage orat the same speed as intact ABA-deficient sitiens (sit^w) mutantseeds when seeds of both genotypes are imbibed on polyethyleneglycol (PEG) solutions of –0.3 to –1.5 MPa osmoticpotential. However, if the thicker testas of wild-type seedsare removed (stripped) from the micropyle without damaging theendosperm, both the percentage and speed of germination at lowexternal water potential are similar to that of sit^w mutantseeds. Removing the micropylar end of the testa from sit^w seedsdid not enhance either the speed or percentage of germinationon PEG solution. Despite similar germination percentage and speed between strippedwild-type seeds and either stripped or intact sit^w seeds underosmotic stress, some differences in seed metabolism are evidentbetween genotypes. The activity of endo-ß-mannanasewas greater in the endosperm of sit^w mutant seeds compared tothe endosperm of wild-type seeds when seeds were exposed toosmotic stress. Although     

Endo-β-mannanase activity during dormancy alleviation and germination of white spruce (Picea glauca) seeds

It is not known how embryos of seeds of the Pinaceae protrude from their enclosing tissues to complete germination. Prior to protrusion of the radicle there is an increase in endo-β-1,4-mannanase (EC 3.2.1.78) activity associated with weakening of the micropylar megagametophyte/nucellus from seeds of white spruce ( Picea glauca [Moench.] Voss). Mannanase activity is present as three isoforms (pI values 5.0, 4.8, 4.7) in both the embryo and surrounding structures (megagametophyte and nucellus) prior to and during imbibition. Activity of all the isoforms increases in the chalazal and micropylar megagametophyte during germination. Activity then declines after the testa splits, typically 1 day prior to radicle protrusion, due partially to its leaching from the seed into the surrounding water. Activity increases in the cotyledons and axis as the embryo commences elongation. Seeds from dormant seedlots exhibit a lower germination percentage, relative to seeds from nondormant seedlots, and the force necessary for the embryo to puncture the surrounding structures tends to be greater. Although similar mannanase activities are present in unimbibed seeds of dormant and nondormant seedlots, during germination, enzyme activity in seeds of dormant seedlots is lower. Moist chilling alleviates dormancy in the seeds of the Pinaceae and, during 3 weeks of this treatment, mannanase activity slowly increases. After 3 weeks of moist chilling and regardless of whether the seedlot was dormant or not prior to moist chilling, the force necessary to puncture the micropylar megagametophyte and nucellus is lower, and the speed of germination greater. Seeds from previously dormant seedlots also complete germination to a greater percentage, relative to unchilled seeds from dormant seedlots. Upon transfer to 25°C, mannanase activity in moist-chilled seeds decreases during germination of all seedlots regardless of their previous dormancy status.     

Sym2 of Pea Is Involved in a Nodulation Factor-Perception Mechanism That Controls the Infection Process in the Epidermis

In pea (Pisum sativum) up to 50 nodulation mutants are known, several of which are affected in the early steps of the symbiotic interaction with Rhizobium sp. bacteria. Here we describe the role of the sym2 gene in nodulation (Nod) factor perception. Our experiments show that the sym2A allele from the wild pea variety Afghanistan confers an arrest in infection-thread growth if the Rhizobium leguminosarum bv viciae strain does not produce Nod factors with a NodX-mediated acetylation at their reducing end. Since the induction of the early nodulin gene ENOD12 in the epidermis and the formation of a nodule primordium in the inner cortex were not affected, we conclude that more than one Nod factor-perception mechanism is active. Furthermore, we show that sym2A-mediated control of infection-thread growth was affected by the bacterial nodulation gene nodO.     

Assessment of clinical competence using objective structured examination.

To avoid many of the disadvantages of the traditional clinical examination we have introduced the structured clinical examination. In this students rotate round a series of stations in the hospital ward. At one station they are asked to carry out a procedure, such as take a history, undertake one aspect of physical examination, or interpret laboratory investigations in the light of a patient''s problem, and at the next station they have to answer questions on the findings at the previous station and their interpretation. As they cannot go back to check on omissions multiple-choice questions have a minimal cueing effect. The students may be observed and scored at some stations by examiners using a check list. In the structured clinical examination the variables and complexity of the examination are more easily controlled, its aims can be more clearly defined, and more of the student''s knowledge can be tested. The examination is more objective and a marking strategy can be decided in advance. The examination results in improved feed-back to students and staff.     

Inhibition of Virus Release by Antibodies to Surface Antigens of Influenza Viruses

When influenza virus was mixed with antisera to its surface subunits before inoculation of cell cultures, anti-hemagglutinin antibodies neutralized infectivity but anti-neuraminidase did not. When the antisera were added after infection of cell cultures, anti-hemagglutinin and anti-neuraminidase antibodies were equally effective in reducing virus titers in culture fluids. Decreased virus titers were not due to interference of antibody with assay and were not accompanied by a reduction in the synthesis of hemagglutinin and neuraminidase subunits. Both antisera also effectively prevented in vitro virus spread. Inhibition of virus release by neuraminidase antibody appeared unrelated to its antienzyme property. Hydrolysis of N-acetyl neuraminic acid residues of infected host cells proceeded unimpaired in the presence of subunit antisera. Anti-hemagglutinin and anti-neuraminidase antibodies may act to prevent virus release by binding newly formed virus subunits to each other and to anti-genically altered cell membranes.     

A difference in sensitivity to alpha-adrenergic agonists exhibited by detrusor and bladder neck of rabbit.

In cumulative dose-response studies, strips from bladder neck of rabbit were significantly more sensitive to stimulation with noradrenaline, phenylephrine, and methoxamine than were strips from detrusor. There was no difference between the two regions in sensitivity to isoprenaline or carbachol. From the known characteristics of these agents, it seemed unlikely that metabolic destruction or uptake could account for the different sensitivities seen. Also, neither normetanephrine nor desmethylimipramine could alter significantly the potency of noradrenaline in either area of the bladder. It seems likely that the difference in sensitivity to alpha-adrenoceptor stimulation in the bladder neck and detrusor is due to factors at the receptor level.