[Ultra-low laparoscopic rectal resection and colo-anal anastomosis. Experimental study on swine]

Nowadays oncologic surgery is defining new criteria in the treatment of rectal cancer: preservation of sfincterial function, ultra-low resections with distal margin at only 2 cm distally to the tumor, role of mesorectum as preferential site of lymphatic diffusion, preservation of lombo-aortic and pelvic nerves. Laparoscopy is showing good results in bowel surgery so as previously got on biliary tract: less visceral manipulation, less stimulation of immunologic system, less pain, early resumption of peristalsis and food intake, better recovery, less hospital stay. We experimented on pig ultra-low laparoscopic resection of the rectum, with preservation of sfincterial function, and mechanical anastomosis at the upper edge of the sfincterial ring. The evaluation of surgical technique, post-operative supervision, and follow-up instrumental control (anal manometry, endo-rectal ultrasonography, sfincterial electtromanometry, Rx barium enema) show technical feasibility and confirm a better recovery with regular defecatory function.

Complete sequence of the mitochondrial DNA in the sea urchin Arbacia lixula: conserved features of the echinoid mitochondrial genome

The complete nucleotide sequence (15,719 nucleotides) of the mitochondrial DNA (mtDNA) from the sea urchin Arbacia lixula is presented. The comparison of gene arrangement between different echinoderm orders of the same class provides evidence that the gene organization is conserved within the same echinoderm class. The peculiarities of sea urchin mtDNA features, already described, are confirmed by the A. lixula mtDNA sequence. The comparison of the entire sequences of mtDNA among A. lixula, Paracentrotus lividus, and Strongylocentrotus purpuratus allowed us to detect peculiar features, common to the three sea urchin species, that can represent the molecular signature of the mt genome in the sea urchin group. Analysis of the nucleotide composition indicates that A. lixula mtDNA, in contrast with the mtDNA of other sea urchins, shows a bias in the use of T and tends to avoid the use of C, most evident in the neutral part of the molecule, such as the third codon positions. This observation indicates that the three sea urchin mtDNAs evolve under different mutation pressure. Analysis of the sequence evolution allowed us to confirm the phylogenetic tree. However, the absolute divergence time, calculated on the basis of paleontological estimates, largely diverged from the expected one.

Evolutionary origin of nonuniversal CUGSer codon in some Candida species as inferred from a molecular phylogeny

CUG, a universal leucine codon, has been reported to be read as serine in various yeast species belonging to the genus Candida. To gain a deeper insight into the origin of this deviation from the universal genetic code, we carried out a phylogenetic analysis based on the small-subunit ribosomal RNA genes from some Candida and other related Hemiascomycetes. Furthermore, we determined the phylogenetic relationships between the tRNA(Ser)CAG, responsible for the translation of CUG, from some Candida species and the other serine and leucine isoacceptor tRNAs in C. cylindracea. We demonstrate that the group of Candida showing the genetic code deviation is monophyletic and that this deviation could have originated more than 150 million years ago. We also describe how phylogenetic analysis can be used for genetic code predictions.

A 67-kDa protein binding to the curved DNA in the main regulatory region of the rat mitochondrial genome

We have purified, by sequence-specific affinity chromatography, a mitochondrial (mt) matrix protein which binds to the curved DNA located between the replication origin (ori) of the leading strand (ori-H) and the two transcription promoters in the rat mt genome. The protein was characterized by gel electrophoresis as a 67-kDa polypeptide and seems to be involved in the DNA contact on the mt light strand. This protein differs (in the size and location of its DNA-binding site) from other DNA-binding proteins studied so far in animal mt systems. We suggest a role for the 67-kDa protein, assisted by other proteins, in regulating the initiation of leading-strand replication.

Molecular classification of living organisms

Recent studies in molecular evolution have generated strong conflicts in opinion as to how world living organisms should be classified. The traditional classification of life into five kingdom has been challenged by the molecular analysis carried out mostly on rRNA sequences, which supported the division of the extant living organisms into three major groups: Archaebacteria, Eubacteria, and Eukaryota. As to the problem of placing the root of the tree of life, the analysis carried out on a few genes has provided discrepant results. In order to measure the genetic distances between species, we have carried out an evolutionary analysis of the glutamine synthetase genes, which previously have been revealed to be good molecular clocks, and of the small and large rRNA genes. All data demonstrate that archaebacteria are more closely related to eubacteria than to eukaryota, thus supporting the classical division of living organisms into two main superkingdoms, Prokaryota and Eukaryota.

Glutamine synthetase gene evolution in bacteria

The evolution of the prokaryotic glutamine synthase (GS) genes, namely the GSI and GSII isoforms, has been investigated using the second codon positions, which have previously proven to behave as a good molecular clock. Our data confirm the early divergence between prokaryotic and eukaryotic GSII before the splitting between plants and animals. The phylogenetic tree of the GSI isoforms shows Archaebacteria to be more closely related to Eubacteria than to Eukaryotes. This finding is confirmed by the phylogenetic analysis carried out on both large and small subunits of rRNA. However, differently from the rRNA analyses, Crenarchaeota and Euryarchaeota Archaebacteria, as well as high- and low-GC gram-positive bacteria, appear to be polyphyletic. We provide evidence that the observed polyphyly of Archaebacteria might be only apparent, resulting from a gene duplication event preceding the split between Archaebacteria and Eubacteria and followed by the retention of only one isoform in the extant lineages. Both gram-negative bacteria and high-GC gram-positive bacteria, which appear closely related, have GS activity regulated by an adenylylation/deadenylylation mechanism. A lateral gene transfer from Archaebacteria to low-GC eubacteria is invoked to explain the observed polyphyly of gram-positive bacteria.

RNase mitochondrial RNA processing cleaves RNA from the rat mitochondrial displacement loop at the origin of heavy-strand DNA replication

Ribonuclease mitochondrial RNA processing cleaves RNAs from the mammalian mitochondrial main non-coding regulatory region, called the displacement loop. Our data demonstrate that rat cells contain a site-specific ribonuclease mitochondrial RNA processing activity. We found that this enzyme processes the rat mitochondrial displacement-loop RNA substrate at the level of the conserved sequence block 1, a result which is different from that for mouse. This finding correlates with the in-vivo transcriptional analysis of the rat displacement-loop region. Processing by homologous and heterologous ribonuclease mitochondrial RNA enzymes occurs in the same manner, suggesting a conserved mode of substrate recognition.

Evolutionary analysis of cytochrome b sequences in some Perciformes: evidence for a slower rate of evolution than in mammals

To obtain information relative to the phylogenesis and microevolutionary rate of fish mitochondrial DNA, the nucleotide sequence of cytochrome b gene in seven fish species belonging to the order of Perciformes was determined. Sequence analysis showed that fish mitochondrial DNA has a nucleotide compositional bias similar to that of sharks but lower compared to mammals and birds. Quantitative evolutionary analysis, carried out by using a markovian stochastic model, clarifies some phylogenetic relationships within the Perciformes order, particularly in the Scombridae family, and between Perciformes, Gadiformes, Cypriniformes, and Acipenseriformes. The molecular clock of mitochondrial DNA was calibrated with the nucleotide substitution rate of cytochrome b gene in five shark species having divergence times inferred from paleontological estimates. The results of such analysis showed that Acipenseriformes diverged from Perciformes by about 200 MY, that the Perciformes common ancestor dates back to 150 MY, and that fish mitochondrial DNA has a nucleotide substitution rate three to five times lower than that of mammals.

The evolution of mitochondrial DNA

Although the massive sequencing of mitochondrial DNA from various organisms, together with studies of a different nature, has contributed enormously to the knowledge of the organization and function of this cytoplasmic genome, many issues, mainly the relationships with the nuclear genome, remain unsolved. This review critically evaluates the most recent advances in research on the evolution of the mitochondrial DNA from a qualitative and quantitative point of view, underlining the multiplicity of structures and genetic organization of this genome, which contrasts with its reduced, but rather constant, information content in various organisms. It also highlights the role that mitochondrial DNA is now playing, particularly in metazoans, in different disciplines and application fields. Among these, particular attention is focused on the discovery of the mitochondrial origin of several diseases affecting primarily the neuromuscular system.

Transcription of rat mitochondrial NADH-dehydrogenase subunits. Presence of antisense and precursor RNA species

We have characterized the transcriptional pattern of the rat mitochondrial ND6-containing region in vivo. We have identified a stable polyadenylated RNA species complementary for the full length of the ND6 mRNA. The analysis of the ND5 region has revealed the presence of an antisense RNA only at its 3' end. The presence of these stable antisense species complementary to structural genes is intriguing and suggests a possible regulatory function. The quantitative analyses have demonstrated that the H transcripts, both codogenic and non-codogenic, are more stable than the L transcripts. We have defined the 5' end of the ND6 mRNA at the level of the ATG downstream of the tRNA(Glu). The mapping of the ND1 5' end has demonstrated that GTG is the first codon of the mRNA. Our findings suggest that the post-transcriptional mechanisms involved in the expression of the mt genome are much more numerous and complex than those already described in the literature.

Linguistic approaches to the analysis of sequence information

Biological macromolecules have many features that resemble modern languages. Thus, linguistic approaches to the analysis of sequence information are becoming powerful tools for deciphering genetic texts. The methodologies used, to date, to determine the global parameters of the genetic language and meaningful patterns within it are described.

[Roux-en-Y reconstruction with defunctionalized jejunal loop, after gastric resection]

Authors report their personal experience on Roux-en-Y reconstruction, after partial gastric resection. They have considered 39 patients: 24 of them had been operated for a peptic ulcer of the lesser gastric curve and 15 for a pyloric cancer for which a partial gastric resection had been adopted for various reasons (age, stage or else). The follow-up lasted on an average of 42 months (4 to 68). Controls concerned secretory activity and motility. A prolonged stasis of solids, in the gastric stump or in the isolated loop, has been observed in two of the long controlled patients, together with superficial ulcers of the digiunal mucosa. Alcaline reflux was absent or very small; inflammatory changes of the gastric mucosa were hardly evident. In conclusion the authors regard the partial gastric resection, followed by the reconstruction with a digiunal isolated loop, as a valid surgical technique, for peptic ulcers of lesser gastric curve and for gastric cancers for which total gastrectomy seems not indicate.

Detection of novel transcripts in the human mitochondrial DNA region coding for ATPase8-ATPase6 subunits

We have analyzed the tRNA(Lys), ATPase8, ATPase6, COIII region of mitochondrial DNA in several human tissues. Beside the mature tRNA(Lys), ATPase8 and ATPase6 common mRNA, and COIII mRNA, we have characterized two new transcripts, called RNA 20 and RNA 21. The RNA 20 is a precursor species which contains the tRNA(Lys) plus the ATPase8 and ATPase6 common mRNA; the RNA 21 is an RNA species shorter than the ATPase8 and ATPase6 common mRNA. The relative concentration of the mature with respect to that of the new species proved different in the various tissues. These findings provide new insights into the mitochondrial transcription mechanism opening the question of a possibly regulatory role of the processing on the expression of the mitochondrial genome.

Sequence analysis and compositional properties of untranslated regions of human mRNAs

A detailed computer analysis of the untranslated regions, 5'-UTR and 3'-UTR, of human mRNA sequences is reported. The compositional properties of these regions, compared with those of the corresponding coding regions, indicate that 5'-UTR and 3'-UTR are less affected by the isochore compartmentalization than the corresponding third codon positions of mRNAs. The presence of higher functional constraints in 5'-UTR is also reported. Dinucleotide analysis shows a depletion of CpG and TpA in both sequences. A search for significant sequence motifs using the WORDUP algorithm reveals the patterns already known to have a functional role in the mRNA UTR, and several other motifs whose functional roles remain to be demonstrated. This type of analysis may be particularly useful for guiding site-directed mutagenesis experiments. In addition, it can be used for assessing the nature of anonymous sequences now produced in large amounts in megabase sequencing projects.

The peculiar evolution of apolipoprotein(a) in human and rhesus macaque

Apo(a) is a low density lipoprotein homologous to plasminogen and has been shown to be involved in coronary atherosclerosis. In the present paper we will try to analyze the interesting evolutionary pattern of Apo(a). The plasminogen gene contains 5 cysteine-rich sequences, called kringles, followed by a protease domain. Apo(a), probably arisen by duplication of an ancestral plasminogen gene, contains many tandemly repeated copies of a sequence domain similar to the fourth kringle of plasminogen, 37 in human and at least 10 in the partially sequenced gene of rhesus, and the protease domain. We have found that the upstream kringles of apo(a) undergo Molecular Drive-like processes that produce high intraspecies similarity, whereas the downstream kringles evolve in a molecular clock-like manner and show an high interspecies sequence similarity. The latter regions are obviously suitable for dating the duplication event by which Apo(a) arose from plasminogen, but only if they evolve at the same rate in the two genes. Thus, we propose a "Molecular Clock Test" for assessing whether the comparison of two paralogous genes (or gene regions) can give reliable information on the dating of their origin by duplication. Applying this test to the kringle-4 domain of apo(a) and plasminogen gene, we demonstrate that the separation between the two genes by duplication dates back at about 90 Mya immediately before the radiation of mammals.

[Segmental liver transplantation. Experimental studies in swine]

Authors report the results of an experimental application of one of the more recent techniques of liver transplantation, which has the preparation ex situ as a basilar step of the procedure. 18 pig were operated on, from september 1991 to march 1993; they were divided in two groups: the first (group A) underwent an auxiliary segmental autotransplantation of left lobe to heterotopic subdiaphragmatic location; in group B an orthotopic segmental autotransplantation of right lobe after ex situ preparation of the liver according the technique of Pichlmayr was performed. The results show that a bigger application of ex situ surgery may help to find a resolution to the problem of the small number of liver donation.

Time and biosequences

In this paper we discuss and demonstrate the importance of several factors relative to the relationship between time and evolution of biosequences. In both quantitative and qualitative measurements of the genetic distances, the compositional constraints of the nucleotide sequences play a very important role. We demonstrate that when homologous sequences significantly differ in base composition we get erratic branching order and/or wrong evaluation of the evolutionary rates. We must consider that every gene may have a different evolutionary dynamic along its sequence, generally linked to its functional constraints; this too can seriously affect its clock-like behavior. We report some cases showing how these factors can affect the quantitative measurements of the genetic distances of biosequences.

Cytochrome oxidase subunit III from Arbacia lixula: detection of functional constraints by comparison with homologous sequences

In this paper we report the comparison of the sequences of the cytochrome oxidase subunit III from three different sea urchin species. Both nucleotide and amino acid sequences have been analyzed. The nucleotide sequence analysis reveals that the sea urchin sequences obey some rules already found in mammals. The base substitution analysis carried out on the sequences of the three species pairs, shows that the evolutionary dynamics of the first and the second codon positions are so slow that do not allow a quantitative measurement of their genetic distances, thus demonstrating that also in these species the COIII gene is strongly conserved during evolution. Changes occurring at the third codon positions indicate that the three species evolved from a common ancestor under different directional mutational pressure. The multi-alignment of the sea urchin proteins indicates the existence of the amino acid sequence motif N R T that represents a possible glycosylation site. Another glycosylation site has been detected in the mammalian cytochrome oxidase subunit III, in a position slightly different. Such an analysis revealed, for the first time, a new functional aspect of this sequence.

The evolution of the mitochondrial D-loop region and the origin of modern man

The origin of modern man is a highly debated issue that has recently been tackled by using mitochondrial DNA sequences. The limited genetic variability of human mtDNA has been explained in terms of a recent common genetic ancestry, thus implying that all modern-population mtDNAs originated from a single woman who lived in Africa less than 0.2 Mya. This divergence time is based on both the estimation of the rate of mtDNA change and its calibration date. Because different estimates of the rate of mtDNA evolution can completely change the scenario of the origin of modern man, we have reanalyzed the available mitochondrial sequence data by using an improved version of the statistical model, the "Markov clock," devised in our laboratory. Our analysis supports the African origin of modern man, but we found that the ancestral female from which all extant human mtDNAs originated lived in a time span of 0.3-0.8 Mya. Pushing back the date of the deepest root of the human implies that the earliest divergence would have been in the Homo erectus population.

WORDUP: an efficient algorithm for discovering statistically significant patterns in DNA sequences

We present here a fast and sensitive method designed to isolate short nucleotide sequences which have non-random statistical properties and may thus be biologically active. It is based on a first order Markov analysis and allows us to detect statistically significant sequence motifs from six to ten nucleotides long which are significantly shared (or avoided) in the sequences under investigation. This method has been tested on a set of 521 sequences extracted from the Eukaryotic Promoter Database (2). Our results demonstrate the accuracy and the efficiency of the method in that the sequence motifs which are known to act as eukaryotic promoters, such as the TATA-box and the CAAT-box, were clearly identified. In addition we have found other statistically significant motifs, the biological roles of which are yet to be clarified.

A statistical method for detecting regions with different evolutionary dynamics in multialigned sequences

We describe a stochastic method for tracing the evolutionary pattern of multialigned sequences. This method allows us to detect gene regions with distinct evolutionary dynamics, e.g., regions that significantly deviate from the expected behavior. Accurate detection of hypervariable or hyperconstrained regions may provide useful information on the structure/function relationship of biosequences. This information can help localize functional constraints. In addition, the selection of distinct evolutionary dynamics may assist in the correct use of biosequences as reliable molecular clocks.