Nuclear matrix of the most primitive eukaryote Archezoa

Accumulating evidence suggests that unicellularArchezoa are the most primitive eukaryotes and their nuclei are of significance to the study of evolution of the eukaryotic nucleus. Nuclear matrix is an ubiquitous important structure of eukaryotic nucleus; its evolution is certainly one of the most important parts of the evolution of nucleus. To study the evolution of nuclear matrix, nuclear matrices ofArchezoa are investigated.Giardia lamblia cells are extracted sequentially. Both embedment-free section EM and whole mount cell EM of the extracted cells show that, like higher eukaryotes, this species has a residual nuclear matrix in its nucleus and rich intermediate filaments in its cytoplasm, and the two networks connect with each other to form a united network. But its nuclear matrix does not have nucleolar matrix and its lamina is not as typical as that of higher eukaryotes; Western blotting shows that lamina ofGiardia and two otherArchezoa Entanzoeba invadens andTrichomonas vaginali all contain only one polypeptide each which reacts with a mammalia anti-lamin polyclonal serum and is similar to lamin B (67 ku) of rnammiia in molecular weight. According to the results and references, it is suggested that nuclear matrix is an early acquisition of the eukaryotic nucleus, and it and the “eukaryotic chromatin” as a whole must have originated very early in the process of evolution of eukaryotic cell, and their origin should be an important prerequisite of the origin of eukaryotic nucleus: in the lamin (gene) family, B-type lamins (gene) should be the ancestral typz and that A-type lamins (gene) might derive therefrom. Project supported by the National Natural Science Foundation of China (Grant No. 3870254).     

Nuclear matrix of the most primitive eukaryote Archezoa

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Location of B- and Z-DNA in the chromosomes of a primitive eukaryote dinoflagellate

The usual conformation of DNA is a right-handed double helix (B-DNA). DNA with stretches of alternating purine-pyrimidine (G-C or A-T) can form a left-handed helix (Z-DNA). The transition B----Z, facilitated by the presence of divalent cations, cytosine methylation, or constraints on DNA such as superhelicity may play a role in the regulation of gene expression and/or in DNA compaction (Zarling, D. A., D. J. Arndt-Jovin, M. Robert-Nicoud, L. P. McIntosh, R. Tomae, and T. M. Jovin. 1984. J. Mol. Biol. 176:369-415). Divalent cations are also important in the structure of the quasi-permanently condensed chromosomes of dinoflagellate protists (Herzog, M., and M.-O. Soyer. 1983. Eur. J. Cell Biol. 30:33-41) which also have superhelicity in their DNA. The absence of histones in dinoflagellate chromosomes suggest that the search for Z-DNA sequences might be fruitful and could provide one indication of the physiological role of this particular DNA conformation. We report a complete immunofluorescent and immunogold analysis of the nuclei of the dinoflagellate Prorocentrum micans E. using monoclonal and polyclonal anti-B and anti-Z-DNA antibodies. Positive labeling was obtained with immunofluorescence using squash preparations and cryosections, both of which showed the intranuclear presence of the two DNA conformations. In ultrathin sections of aldehyde-prefixed, osmium-fixed, and epoxy-embedded cells, we have localized B-DNA and Z-DNA either with single or double immunolabeling using IgG labeled with 5- and 7-nm gold particles, respectively. Chromosomal nucleofilaments of dividing or nondividing chromosomes, as seen in ultrathin sections in their arch-shaped configuration, are abundantly labeled with anti-B-DNA antibody. Extrachromosomal anti-B-DNA labeling is also detected on the nucleoplasm that corresponds to DNA loops; we confirm the presence of these loops previously described external to the chromosomes (Soyer, M.-O., and O. K. Haapala. 1974. Chromosoma (Berl.). 47:179-192). B labeling is also visible in the nucleolus organizer region (NOR) and in the fibrillo-granular area (containing transcribing rDNA) of the nucleolus. Z-DNA was localized in limited areas inside the chromosomes, often at the periphery and near the segregation fork of dividing chromosomes. In the nucleolus, Z-DNA is observed only in the NOR area and never in the fibrillo-granular area. For both types of antibody experiments, controls using gold-labeled IgG without primary antibody were negative. A quantitative evaluation of the distribution of the gold-labeled IgG and a parametric test support the validity of these experiments.(ABSTRACT TRUNCATED AT 400 WORDS)     

Stress-induced tRNA-derived RNAs: a novel class of small RNAs in the primitive eukaryote Giardia lamblia

Giardia lamblia is an early diverging and evolutionarily successful protozoan as it can enter into a dormant cyst stage from a vegetative trophozoite. During dormant stage, its metabolic rate decreases dramatically. However, to date, the regulatory molecules participating in the initiation and maintenance of this process have not been fully investigated. In this study, we have identified a class of abundant small RNAs named sitRNAs, which are approximately 46 nucleotides in length and accumulate in G. lamblia encysting cultures. Remarkably, they are derived from the 3' portion of fully matured tRNAs by cleavage of the anticodon left arm, with the 3' terminal CCA triplex still connected. During differentiation, only a limited portion of mature tRNAs is cleaved, but this cleavage occurs almost in the entire tRNA family. sitRNAs begin to accumulate as early as 3 h after initiation of encystation and are maintained at a relatively stable level during the whole process, exhibiting an expression peak at around 24 hr. Our studies further show that sitRNAs can be induced by several other stress factors, and in the case of serum deprivation, both tRNAs and sitRNAs degrade rapidly, with the accumulation of tRNA being halved. Our results may provide new insight into a novel mechanism for stressed G. lamblia to regulate gene expression globally.     

Storage glucan and glucosyltransferase isozymes of cyanidioschyzon merolae: A primitive eukaryote

Cyanidioschyzon merolae, a primitive eukaryotic alga isolated from supposedly pure cultures of the thermoacidophilic alga, Cyanidium caldarium, has many of the characteristics of such prokaryotes as bacteria and the cyanobacteria. Cyanidioschyzon appears to have even more of these prokaryotic features than does Cyanidium. Cyanidioschyzon divides by binary fission as do most bacteria. Its thylakoids are arranged along the periphery of the cell, like the cyanobacteria. Its formation of storage glucan, as well as the type of sugar formed is more like that of the blue-green algae rather than that of the red algae. Cyanidioschyzon merolae may be much more primitive than Cyanidium caldarium, and could be the most primitive eukaryotic cell.     

Metabolic evolution in response to interspecific competition in a eukaryote

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Spacing requirements for simultaneous recognition of the adenovirus major late promoter TATAAAAG box and initiator element

The distance between the TATAAAAG box and initiator element of the strong adenovirus major late promoter was systematically altered to determine the optimal spacing for simultaneous recognition of both elements. We find that the TATAAAAG element is strongly dominant over the initiator for specification of the start site. The wild type spacing of 23 base pairs between TATAAAAG and +1A is optimal for promoter strength and selective recognition of the A-start. Initiation is constrained to a window spaced 19-26 base pairs downstream of (-31)-TATAAAAG-(-24), and A-starts are favored over alternate starts only when spaced between 21 and 25 base pairs downstream of TATAAAAG. We report an expanded TATAAAAG and initiator promoter consensus for vertebrates and plants. Plant promoters of this class are (A-T)-rich and have an A-rich (non-template strand) core promoter sequence element downstream of +1A.     

Identification of 20 snoRNA-like RNAs from the primitive eukaryote, Giardia lamblia

From a specialized cDNA library of Giardia lamblia, 20 snoRNA-like RNAs, including 16 box C/D sRNAs and four box H/ACA sRNAs, were first identified. The sRNAs were predicted to guide a total of 11 2′-O-methylation and four pseudouridylation sites on the G. lamblia rRNAs, respectively. By using primer extension assay, seven methylation sites were precisely mapped in the G. lamblia 16S rRNA, despite its high GC content. All of the sRNA genes locate on the small intergenic regions of the G. lamblia genome and seem to be independently transcribed from their own promoters. Particularly, a cluster composed of GlsR17 and GlsR18 genes is transcribed as a dicistronic precursor, implying a mechanism of endonuclease cleavage for the maturation of the two sRNAs. The systematic identification of the sRNAs in G. lamblia has provided valuable information about the characteristics of the two major families of small guide RNAs in one of the most primitive eukaryotes and would contribute to the understanding of the evolution of small non-messenger RNA genes from prokaryotes to eukaryotes.     

New remains of primitive ruminants from Thailand: evidence of the early evolution of the Ruminantia in Asia

A new tragulid, Archaeotragulus krabiensis , gen. n. et sp. n., is described from the late Eocene Krabi Basin (south Thailand). It represents the oldest occurrence of the family which was previously unknown prior to the Miocene. Archaeotragulus displays a mixture of primitive and derived characters, together with the M structure on the trigonid, which appears to be the main dental autapomorphy of the family. We also report the occurrence at Krabi of a new Lophiomerycid, Krabimeryx primitivus , gen. n. et sp. n., which displays affinities with Chinese representatives of the family, particularly Lophiomeryx . The familial status of Iberomeryx is discussed and a set of characters is proposed to define both Tragulidae and Lophiomerycidae. Results of phylogenetic analysis show that tragulids are monophyletic and appear nested within the lophiomerycids. The occurrence of Tragulidae and Lophiomerycidae in the upper Eocene of south-east Asia enhances the hypothesis that ruminants originated in Asia, but it also challenges the taxonomic status of traguloids within the Ruminantia.