Association of Viral Reverse Transcriptase with an Enzyme degrading the RNA Moiety of RNA-DNA Hybrids

DURING replication of RNA tumour viruses, the genetic information contained in the viral RNA seems to be transferred to DNA^1,2. Studies on the enzymatic activities present in the virus particles suggest that this transfer is mediated by an RNA dependent DNA polymerase^3,4. RNA-DNA hybrids have been demonstrated to occur as intermediates in this reaction⁵ and single stranded DNA is generated as an early reaction product⁶, which is then replicated to give a double stranded DNA product^6–8. The mechanism by which the single stranded DNA is displaced from the RNA template is, however, not known.     

草菇减数分裂和担孢子形成细胞核行为

本文用苏木精染色和双苯并咪唑(Hoechst 33258)染色法,从草菇子实体“纽期”菌褶分化完开始,每3小时对同一个子实体连续切取菌褶进行染色观察。结果表明草菇子实体“纽期”菌褶形成时,约10％的担子发生了核配;在子实体发育过程中,尤其是子实体成熟期后,不断有少量新的双核担子产生,并发生核配,使草菇减数分裂的同步性不高;草菇从菌褶分化完成(此时已有10％担子发生核配)到子实体完全成熟,菌褶变成深粉红至褐色(此时约70％担子完成减数分裂)需要28—30小时;担子减数分裂的持续时间为18小时,其中细线期和偶线期5.9小时、粗线期6.2小时、双线期和终变期3.4小时、中期10.5小时、后期Ⅰ到四分体2小时;经过对粗线期、双线和终变期以及中期Ⅰ染色体条数的多次反复观察,认为草菇的染色体条数为11(n=11);减数分裂后,4个子核分别进入4个担孢子中,留下无核的担子;绝大部分担孢子是单核的,有约5％的担孢子是双核的。     

Chalazal germination inTrichodesma amplexicaule Roth.

Seed germination studies onTrichodesma amplexicaule were carried out. Seeds show abnormal behaviour of germination which is termed "Chalazal germination". This abnormal behaviour of germination is due to the presence of an obturator at the micropylar end. Seeds showed maximum (60 per cent) germination with 110 min concentrated H₂SO₄ treatment.     

裸子植物psbA基因分子进化式样的研究

为阐明裸子植物对陆生生境生态响应的分子机制,以新近的裸子植物分类系统为指导,基于psb A基因编码全序列对4亚纲53种代表植物进行分子进化分析。首先,依据"放松分子钟"模型重建裸子植物在时间尺度下系统发育关系;其次,采用6个模型(MEC/JTT、MEC/cp REV、M5、M7、M8、M8a)估测氨基酸位点ω值,并对各模型结果进行统计检测;随后,利用Bootstrap方法检PSBA蛋白内部氨基酸位点的共进化动态。结果表明,系统树提示的物种分化历程支持前期分类结果;光合系统反应中心核心PSBA蛋白有3个氨基酸位点(13、19和243)曾经受正选择压力;PSBA蛋白内部有多对氨基酸位点间构成了共进化网络。因此,psb A基因编码序列具有作为描绘裸子植物系统发育关系标记的潜力,PSBA蛋白部分位点经历了适应性进化,通过位点间共进化网络协同作用方式辅助裸子植物响应陆生生境。     

SIRT1-ZEB1-positive feedback promotes epithelial-mesenchymal transition process and metastasis of osteosarcoma

Osteosarcoma is the most common malignant bone cancer that mainly affects children and young adults. Recently, the NAD⁺-dependent deacetylase, sirtuin 1 (SIRT1), has been reported to play a key role in the development of malignant tumors. The study aimed to investigate the role of SIRT1 in osteosarcoma and explore its underlying oncogenic mechanisms. The prognostic value of SIRT1 in osteosarcoma was assessed through detection of SIRT1 expression based on osteosarcoma biopsy tissue. Then, to further investigate the effect of SIRT1 in osteosarcoma, osteosarcoma cells were treated with small interfering RNA SIRT1 and overexpressed SIRT1 to detect the cell migration, invasion, and epithelial-mesenchymal transition (EMT). The levels of SIRT1 expression were significantly higher in osteosarcoma tissues than those in adjacent normal tissues, and the SIRT1 protein level may be coupled with metastatic and poor prognosis risk in patients with osteosarcoma. Moreover, SIRT1 silencing inhibited the migration as well as invasion ability of osteosarcoma cells in vitro, and SIRT1 upregulation reversed those effects. Finally, we found that SIRT1-ZEB1-positive feedback enhanced the EMT process and metastasis of osteosarcoma. Altogether, the results of the current study revealed that high levels of SIRT1 might be a biomarker for a high metastatic rate in patients with osteosarcoma, which suggested that inhibition of SIRT1 might be promising for the therapeutics of osteosarcoma.     

A giant rhinocerotoid (Mammalia, Perissodactyla) from the Late Oligocene of north-central Anatolia (Turkey)

A giant rhinocerotoid is described for the first time south of the Black Sea, in Turkey. The single specimen, a fragmentary radius referred to Paraceratherium sp., originates from conglomerates nearby at Gözükizilli, in the Çankiri–Çorum Tertiary basin. These layers correspond to the Lower member of the Kizilirmak Formation. The same locality (Gözükizilli-2) yields also the small rhinocerotid Protaceratherium sp., cf. P. albigense (Roman, 1912). Three other mammal localities (Gözükizilli-1, in the Lower Member of the formation, with several rodent species; Tepe 641 and Kizilirmak, in the Upper Member, with a diversified micro- and macro-mammal fauna) allow us to refer the Kizilirmak Formation as a whole to the Late Oligocene. All the observed taxa have strong Asian and/or European affinities, which precludes any geographical insulation for this part of Anatolia during the Late Oligocene.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 152 , 581–592.     

NEW SPECIES OF PARAPHIOMYS (RODENTIA, THRYONOMYIDAE) FROM THE LOWER MIOCENE OF AS-SARRAR, SAUDI ARABIA

Abstract:  The family Thryonomyidae is represented in the Lower Miocene of Saudi Arabia by a single species, Paraphiomys knolli sp. nov. This new taxon differs from all other thryonomyids in being small, lower molars having a short metalophulid II and an isolated anterolabial cuspid, and upper molars being antero-posteriorly compressed and pentalophodont. A cladistic analysis involving all extinct and extant species of thryonomyids is provided. Paraphiomys knolli branches as the sister-species of Paraphiomys pigotti , type species of the genus.     

厚朴基原植物及其4个近缘种的花粉鉴定

采用扫描电镜对2种厚朴基原植物(厚朴Magnolia officinalis Rehd.et Wils.、凹叶厚朴M.officinalis Rehd.et Wils.var.biloba Rehd.et Wils.)及4种近缘植物(玉兰M.denudata Desr.、紫玉兰M.liliiflora Desr.、望春玉兰M.biondii Pampan.、荷花玉兰M.grandiflora L.)的花粉形态、表面纹饰和大小进行了观察研究。结果显示:(1)6种植物的花粉粒均为单粒,具远极单萌发沟,沟长,直达两端,左右对称,异极;侧面观均为舟形,两端较尖,赤道面观为椭圆形或近椭圆形,极面观均为近圆形;外壁均具小穴状或网状纹饰。(2)厚朴的小穴状纹饰小而浅,不明显;凹叶厚朴的小穴状纹饰小但较深,也不甚明显;相比之下,紫玉兰、玉兰、望春玉兰和荷花玉兰的花粉粒表面密布不规则隆起及深穴点,明显。(3)6种植物花粉粒由大至小依次为:荷花玉兰凹叶厚朴厚朴玉兰紫玉兰望春玉兰。3种不同的花粉处理方法中,自然干燥法能清晰地观察到花粉的扫描电镜特征,此方法优于戊二醛固定法和叔丁醇真空冷冻干燥法。本研究结果为厚朴中药资源的基原植物及其近缘种鉴定提供了新的证据,也为现代植物从种及亚种级水平分类提供了参考。