In analyzing the silent nucleotide substitutions in some mammalian mitochondrial mRNA coding genes, we had found that the frequency of each of the four nucleotides in rat, mouse, and cow, but not in humans, is the same in the silent third codon position (Lanave C, Preparata G, Saccone C, Serio G (1984) J Mol Evol 20:86-93). Because our findings for these three species were compatible with a stationary Markov process for the evolution of nucleotide sequences, we applied such a model to calculate the effective evolutionary silent substitution rate (vs) and the divergence times among the species. In this paper we have analyzed the first and second codon positions in the same mammalian mitochondrial genes. We found that in the first and second codon positions the human mitochondrial genes satisfy the stationarity conditions. This has allowed us to use the stochastic model mentioned above to calculate the divergence times among mouse, rat, cow, and human. Furthermore, we have analyzed the silent substitution rate in one nuclear gene for these four mammals. We found that in this gene the effective silent substitution rate is about 3 times lower than in mitochondrial genes, and that humans are in this case stationary with respect to the other three mammals in the third codon position as well. Application of our Markov model to this latter gene yields divergence times consistent with our previous determinations.

Animals↗

PubMedDate not supplied

Duplication and remoulding of tRNA genes during the evolutionary rearrangement of mitochondrial genomes.

During the evolution of sea urchins, a transfer RNA gene lost its tRNA function and became part of a protein-coding gene. This functional loss of a tRNA with specificity for one group of leucine codons (CUN, where N is any base) was accompanied by the gain of a new tRNA with that specificity. The new tRNA gene for CUN codons appears to have evolved by duplication and divergence from a tRNA gene specific for another group of leucine codons (UUR, where R is a purine). These proposals account for (1) the strong sequence resemblance between the modern tRNA genes for CUN and UUR codons in Paracentrotus, (2) the altered location of the CUN gene in mitochondrial DNA of this urchin, and (3) the persistence of a 72-base pair sequence containing a trace of the old CUN gene at its original location. The old CUN gene now codes for an extra 24 amino acids at the amino end of subunit 5 in NADH dehydrogenase. Besides giving clues about the mechanisms by which tRNA genes move during mitochondrial DNA evolution, this finding leads us to propose a pathway relating the arrangements of other genes in mitochondrial DNAs from four animal phyla.

Animals↗

PubMedDate not supplied

[Histiocytic necrotizing lymphadenitis or Kikuchi-Fujimoto disease. Report of a case].

Histiocytic Necrotising Lymphadenitis by Kikuchi-Fujimoto (NHL) is a rare disease of unknown etiopathogenesis, characterized by cervical lymphadenomegaly, fever and asthenia. It has a good prognosis with a complete functional recovery of the affected lymph nodes. In 1998 a 28 year-old patient (A. G.) was admitted in the Department of Internal Medicine, Garibaldi Hospital, Catania for fever, asthenia and cervical lymphadenopathy. Hemato-chemical tests performed during hospitalization showed only relative leukopenia and a significant increase of ESR. An initial cervical lymph node biopsy made the diagnosis of Hodgkin's lymphoma. However, the favourable clinical course and the normalization of the previous altered hematochemical tests, induced to perform a second lymph node biopsy which led to diagnosis of NHL. The patient was given antibiotics and anti-inflammatory drugs for ten days with a complete healing which persisted at a twelve-month follow-up. The conclusion is drawn that NHL of unknown etiopathogenesis and with a good prognosis is more frequent than what revealed by the data in the literature because of its insidious and aspecific clinical presentation.

Adult↗

PubMedDate not supplied

[Juvenile primary refractory anemia with excess of blasts. Report of a case].

Myelodysplastic syndromes (MDS) are diseases typical of the adult age, characterized by a clonal alteration of the totipotent staminal cell which causes an inefficient hemopoiesis, reduction of bone marrow cell number, increased bone marrow cell destruction, dysplasia of at least two of the three hemopoietic cell lines and by the tendency to evolve towards acute myeloid leukemia (AML). In patients with MSD, particularly in the advanced primary form, single or multiple chromosomal abnormalities can be found frequently, which may show up and/or modify themselves in any moment of the disease (multistep pathogenetic hypothesis) and whose severity influences significantly the prognosis of MSD patients. In November 1998, a 22 year old female patient (C. C.) was admitted to the Department of Internal medicine of the Garibaldi Hospital, Catania for anemia of unknown origin. The normalities of the hematochemical tests and of other instrumental examinations, induces to perform an osteo-medullary biopsy which revealed the presence of a typical MSD, refractory anemia with excess of blasts type. This disease in its primary form is rare in youth and has a high tendency to evolve in AML. The good clinical conditions of the patient, the absence of chromosomal abnormalities, the normal levels of HbF, the short time interval of the initial diagnosis induced to proceed to bone marrow transplantation, that, as shown by the data reported in the international literature, may give her a good quoad vitam prognosis.

Adult↗