Animal evolution and the molecular signature of radiations compressed in time

The phylogenetic relationships among most metazoan phyla remain uncertain. We obtained large numbers of gene sequences from metazoans, including key understudied taxa. Despite the amount of data and breadth of taxa analyzed, relationships among most metazoan phyla remained unresolved. In contrast, the same genes robustly resolved phylogenetic relationships within a major clade of Fungi of approximately the same age as the Metazoa. The differences in resolution within the two kingdoms suggest that the early history of metazoans was a radiation compressed in time, a finding that is in agreement with paleontological inferences. Furthermore, simulation analyses as well as studies of other radiations in deep time indicate that, given adequate sequence data, the lack of resolution in phylogenetic trees is a signature of closely spaced series of cladogenetic events.     

Comment on "Positive selection of tyrosine loss in metazoan evolution"

Tan et al. (Reports, 25 September 2009, p. 1686) argued that loss of tyrosine residues from proteins in metazoans was driven by positive selection to remove potentially deleterious phosphorylation sites. We challenge this hypothesis, providing evidence that the high guanine-cytosine (GC) content of metazoan genomes was the primary driver in the loss of tyrosine residues.     

The premetazoan ancestry of cadherins

Cadherin-mediated cell adhesion and signaling is essential for metazoan development and yet is absent from all other multicellular organisms. We found cadherin genes at numbers similar to those observed in complex metazoans in one of the closest single-celled relatives of metazoans, the choanoflagellate Monosiga brevicollis. Because the evolution of metazoans from a single-celled ancestor required novel cell adhesion and signaling mechanisms, the discovery of diverse cadherins in choanoflagellates suggests that cadherins may have contributed to metazoan origins.     

Precambrian Fossils (?) near Elliot Lake, Ontario

Complex structures in Upper Huronian (Lower Proterozoic) quartzite north of Lake Huron are interpreted as probable metazoan fossils aged between 2 and 2.5 x 10(9) years. They are preserved as sand casts in the form of curved spindles having inclined lateral corrugations, axial marking, and apparent bilateral symmetry.     

The works of living social insects as pseudofossils and the age of the oldest known metazoa

Living organisms are known to create structures in ancient rocks that are indigenous but not primary and that have been mistaken for fossils. Examination of burrows recently reported as fossils from 10(9)-year-old sedimentary rocks indicates that they are not the same age as the rocks but were probably made by termites working down after water. The burrows are partially filled with material from a modern lateritic surface from which they descend into steeply dipping, decomposed silt-stones of the Zambian Copperbelt. In fact, no authentic record of Metazoa that are demonstrably coeval with rocks older than 680 million years is known.     

Proterozoic modular biomineralized metazoan from the Nama Group,Namibia

We describe a Proterozoic, fully biomineralized metazoan from the Omkyk Member (approximately 549 million years before the present) of the northern Nama Group, Namibia. Namapoikia rietoogensis gen. et sp. nov. is up to 1 meter in diameter and bears a complex and robust biomineralized skeleton; it probably represents a cnidarian or poriferan. Namapoikia encrusts perpendicular to the walls of vertical synsedimentary fissures in microbial reefs. This finding implies that large, modular metazoans with biologically controlled mineralization appeared some 15 million years earlier than previously documented.     

The ediacarian period and syste: metazoa inherit the Earth

The Ediacarian, here defined as the initial period and system of the Phanerozoic Eon, is characterized by the oldest known multicellular animal life. The distinctive biotal assemblage comprises naked Metazoa, represented in the type region by 26 species in 18 genera and 4 or more phyla, plus simple metazoan surface tracks. Elements of this unique biota appeared worldwide at low paleolatitudes, following terminal Proterozoic glaciation. Ediacarian history lasted from about 670 million to 550 million years ago. This interval, plus Early Cambrian, was the time during which metazoan life diversified into nearly all of the major phyla and most of the invertebrate classes and orders subsequently known.     

A polarized epithelium organized by beta- and alpha-catenin predates cadherin and metazoan origins

A fundamental characteristic of metazoans is the formation of a simple, polarized epithelium. In higher animals, the structural integrity and functional polarization of simple epithelia require a cell-cell adhesion complex that contains a classical cadherin, the Wnt-signaling protein β-catenin and the actin-binding protein α-catenin. We show that the non-metazoan Dictyostelium discoideum forms a polarized epithelium that is essential for multicellular development. Although D. discoideum lacks a cadherin homolog, we identify an α-catenin ortholog that binds a β-catenin-related protein. Both proteins are essential for formation of the epithelium, polarized protein secretion, and proper multicellular morphogenesis. Thus, the organizational principles of metazoan multicellularity may be more ancient than previously recognized, and the role of the catenins in cell polarity predates the evolution of Wnt signaling and classical cadherins.     

Massive horizontal gene transfer in bdelloid rotifers

Horizontal gene transfer in metazoans has been documented in only a few species and is usually associated with endosymbiosis or parasitism. By contrast, in bdelloid rotifers we found many genes that appear to have originated in bacteria, fungi, and plants, concentrated in telomeric regions along with diverse mobile genetic elements. Bdelloid proximal gene-rich regions, however, appeared to lack foreign genes, thereby resembling those of model metazoan organisms. Some of the foreign genes were defective, whereas others were intact and transcribed; some of the latter contained functional spliceosomal introns. One such gene, apparently of bacterial origin, was overexpressed in Escherichia coli and yielded an active enzyme. The capture and functional assimilation of exogenous genes may represent an important force in bdelloid evolution.     

Polarization of the C. elegans embryo by RhoGAP-mediated exclusion of PAR-6 from cell contacts

Early embryos of some metazoans polarize radially to facilitate critical patterning events such as gastrulation and asymmetric cell division; however, little is known about how radial polarity is established. Early embryos of Caenorhabditis elegans polarize radially when cell contacts restrict the polarity protein PAR-6 to contact-free cell surfaces, where PAR-6 regulates gastrulation movements. We have identified a Rho guanosine triphosphatase activating protein (RhoGAP), PAC-1, which mediates C. elegans radial polarity and gastrulation by excluding PAR-6 from contacted cell surfaces. We show that PAC-1 is recruited to cell contacts, and we suggest that PAC-1 controls radial polarity by restricting active CDC-42 to contact-free surfaces, where CDC-42 binds and recruits PAR-6. Thus, PAC-1 provides a dynamic molecular link between cell contacts and PAR proteins that polarizes embryos radially.     

Turbulence, cleavage, and the naked embryo: a case for coral clones

After mass spawning events, coral embryos, lacking the protective capsule of other metazoans, are directly exposed to the environment at the ocean surface. Here, we present evidence that modest turbulence disrupts the integrity of these embryos, which fragment into totipotent cells that develop into proportionately smaller functional larvae. The level of turbulence required to fragment coral embryos can be generated from small wind-generated waves, which occur frequently during coral spawning on the Great Barrier Reef. The formation of planktonic coral clones, through natural embryo fragmentation of broadcast spawn, is a previously unknown mode of reproduction in the animal kingdom.     

山羊-绵羊种间体细胞核移植重构胚构建

以山羊皮肤成纤维细胞为供体细胞,绵羊去核卵母细胞为受体细胞进行种间体细胞核移植,构建山羊-绵羊重构胚,并对其采用离子霉素联合6-DM AP法和胞质注射绵羊精子提取物法进行激活,比较两种不同激活方法对山羊-绵羊种间体细胞核移植重构胚的激活效果。结果表明,共构建获得山羊-绵羊重构胚238枚,重构胚在体外能够发育至囊胚阶段;离子霉素联合6-DM AP法激活的卵裂率为58.33%(70/120),囊胚发育率为4.28%(3/70);胞质注射绵羊精子提取物法激活的卵裂率为63.55%(75/118),囊胚发育率为6.66%(5/75),两种方法的激活效果差异不显著。     

Lower Cambrian vendobionts from China and early diploblast evolution

Ediacaran assemblages immediately predate the Cambrian explosion of metazoans and should have played a crucial role in this radiation. Their wider relationships, however, have remained refractory and difficult to integrate with early metazoan phylogeny. Here, we describe a frondlike fossil, Stromatoveris (S. psygmoglena sp. nov.), from the Lower Cambrian Chengjiang Lagerst?tte (Yunnan, China) that is strikingly similar to Ediacaran vendobionts. The exquisite preservation reveals closely spaced branches, probably ciliated, that appear to represent precursors of the diagnostic comb rows of ctenophores. Therefore, this finding has important implications for the early evolution of this phylum and related diploblasts, some of which independently evolved a frondose habit.     

Factors Affecting the Efficiency of Embryonic Cell Nuclear Transfer in Rabbits

Factors affecting the efficiency of nuclear transfer （NT） in rabbits were examined in the present study. When 100 V mm of pulse strength and 15 us of pulse duration were employed, 3 and 4 electronic pulses resulted in significantly more cytoplasts fused with donor cells compared with 2 electronic pulses （P〈 0.05）, but no significant difference was found in the cleavage rate of reconstructed embryos among the three groups （P〉0.05）. When the duration and number of electronic pulse were fixed at 15 ps and 3 times, increase of pulse intensity from 100 V mm 1 to 150 V mm^-1 and 200 V mm^-1 resulted in a significantly decrease in the cleavage rate of reconstructed embryos （P〈 0.05）, although the fusion rate did not significantly differ among the three groups （P〉 0.05）. Significantly more reconstructed embryos cleaved and developed to blastocysts when they were derived from donor embryos at the 8-16-cell stage, in comparison with the reconstructed embryos derived from donor embryos at the compact morula stage （P 〈 0.05）, although the fusion rate was similar （P 〉 0.05）. Activation of cytoplasts prior to fusion increased the cleavage rate （P〈 0.05） and blastocyst development （P〈 0.05） of reconstructed embryos, but decreased the fusion rate （P 〈 0.05） compared with cytoplasts activated post fusion. More reconstructed embryos developed to blastocysts when they were cultured in TCM ＋ 3% OCS at the first 48 h and then cultured in TCM199＋ 10% FCS, in comparison with the reconstructed embryos cultured in either TCM199＋ 10% FCS or TCM199＋3% OCS （P 〈 0.05）. When 22 NT embryos were transferred into the oviducts of one recipient rabbit, one recipient rabbit delivered a female rabbit at 34 days of gestation. In conclusion, either electrofusion parameter or developmental stage of donor embryos have a significant effect on the efficiency of NT, NT embryos require different concentration of serum at their different development stages.     

Manipulating the metazoan mitochondrial genome with targeted restriction enzymes

High copy number and random segregation confound genetic analysis of the mitochondrial genome. We developed an efficient selection for heritable mitochondrial genome (mtDNA) mutations in Drosophila, thereby enhancing a metazoan model for study of mitochondrial genetics and mutations causing human mitochondrial disease. Targeting a restriction enzyme to mitochondria in the germline compromised fertility, but escaper progeny carried homoplasmic mtDNA mutations lacking the cleavage site. Among mutations eliminating a site in the cytochrome c oxidase gene, mt:CoI(A302T) was healthy, mt:CoI(R301L) was male sterile but otherwise healthy, and mt:CoI(R301S) exhibited a wide range of defects, including growth retardation, neurodegeneration, muscular atrophy, male sterility, and reduced life span. Thus, germline expression of mitochondrial restriction enzymes creates a powerful selection and has allowed direct isolation of mitochondrial mutants in a metazoan.     

影响兔胚胎细胞核移植效率的因素

 对兔胚胎细胞核移植（NT）的有关影响因素进行了系统研究。结果发现电场强度100 V·mm-1，脉冲时间15μs，电脉冲3～4次的融合率显著高于其它组（P<0.05）；融合前激活卵母细胞，分裂率和囊胚率显著高于融合后激活（P <0.05）；当用8～16-细胞胚胎的卵裂球作供核时，卵裂率和囊胚率显著高于致密桑椹胚卵裂球为供核组；当重组胚在含3%发情牛血清（OCS）的TCM199中培养48 h后，转入含10% FCS的TCM199中继续培养，卵裂率和囊胚率显著高于一直在3% OCS或10% 胎犊血清（FCS）中培养的重组胚（P < 0.05）。将22枚2～4-细胞期重组胚移入同期发情的受体母兔输卵管内，34 d后产下NT仔兔1只。结果表明，电融合参数和供体胚胎的发育阶段以及受体卵母细胞的状态对NT效果有显著影响，在NT胚胎的不同发育阶段采用不同的血清种类和浓度可提高其胚胎发育能力。     

Precambrian Mollusc-like Fossils from Inyo County, California

Probable molluscan fossils have been discovered in the Reed Dolomite, White-Inyo Mountain area, Inyo County, California. They consist of small orthoconic shells with relatively large bilaterally symmetrical protoconch-like initial termini. Some individuals have a 'U-shaped" (in transverse section) internal structure. The fossils occur at least 900 meters below the strata containing the earliest known olenellid trilobites and are therefore considered Precambrian.     

体细胞核移植技术生产转基因猪胚胎的研究

以转染绿色荧光蛋白基因的猪胎儿成纤维阳性细胞作为体细胞核移植的核供体,体外成熟卵母细胞为核移植受体构建绿色荧光蛋白转基因克隆猪胚胎,研究供核细胞的处理、注核部位及重构胚融合/激活时间对转GFP克隆胚早期发育的影响.结果显示,胎儿成纤维细胞血清饥饿与非饥饿培养10 d处理组,采用卵周间隙核移植重构胚的卵裂率（82.35%和79.07%）差异不显著(P >0.05);体外培养42~44 h 卵母细胞进行胞质内和卵周间隙注核的重构胚胎,其卵裂率（81.11%和76.80%）差异不显著（P >0.05）;将卵周间隙注射法构建重构胚在0~1 h,2~4 h 和6~8 h 进行融合/激活操作,前2组重构胚卵裂率（75.61%和83.07%）无显著差异(P >0.05),但显著高于第3组（60.00%）的卵裂率(P <0.05).     

氧分压对猪卵母细胞成熟尧受精及早期胚胎发育的影响

研究利用两种氧分压（5%和20%）培养卵母细胞并进行IVF试验,同时使用两种氧分压培养孤雌（PA）胚胎、体外受精（IVF）胚胎和克隆(NT) 胚胎,以探寻猪的最佳体外培养环境。结果显示：低氧分压不利于猪卵母细胞的体外成熟,其成熟率极显著低于高氧培养的,但对低氧培养的卵母细胞进行IVF时,其卵裂率和囊胚率均极显著高于高氧培养的卵母细胞;IVF进行精卵孵育时,低氧环境下,其胚胎卵裂率和囊胚率均显著高于高氧环境下的;PA胚胎、IVF胚胎和NT胚胎用两种氧分压培养,低氧条件下IVF胚胎的发育能力高于高氧培养的,而PA胚胎和NT胚胎差异不显著。试验结果表明,低氧培养虽不利于卵母细胞的成熟,但有利于其以后的胚胎发育,且低氧环境下IVF胚胎的发育能力高于高氧环境下的。