Male death resulting from hybridization between subspecies of the gypsy moth, Lymantria dispar

We explored the origin of all-female broods resulting from male death in a Hokkaido population of Lymantria dispar through genetic crosses based on the earlier experiments done by Goldschmidt and by testing for the presence of endosymbionts that are known to cause male killing in some insect species. The mitochondrial DNA haplotypes of the all-female broods in Hokkaido were different from those of normal Hokkaido females and were the same as those widely distributed in Asia, including Tokyo (TK). Goldschmidt obtained all-female broods through backcrossing, that is, F1 females obtained by a cross between TK females (L. dispar japonica) and Hokkaido males (L. dispar praeterea) mated with Hokkaido males. He also obtained all-male broods by mating Hokkaido females with TK males. Goldschmidt inferred that female- and male-determining factors were weakest in the Hokkaido subspecies and stronger in the Honshu (TK) subspecies. According to his theory, the females of all-female broods mated with Honshu males should produce normal sex-ratio broods, whereas weaker Hokkaido sexes would be expected to disappear in F1 or F2 generations after crossing with the Honshu subspecies. We confirmed both of Goldschmidt's results: in the case of all-female broods mated with Honshu males, normal sex-ratio broods were produced, but we obtained only all-female broods in the Goldschmidt backcross and obtained an all-male brood in the F1 generation of a Hokkaido female crossed with a TK male. We found no endosymbionts in all-female broods by 4,'6-diamidino-2-phenylindole (DAPI) staining. Therefore, the all-female broods observed in L. dispar are caused by some incompatibilities between Honshu and Hokkaido subspecies.

[Clinical review of supracricoid laryngectomy with CHEP and CHP: 50 patients treated in 11 years]

An analysis of clinical data on 50 patients undergoing supracricoid laryngectomy (SCL) between 1997 and 2008 i.e., cricohyoidoepiglottopexy (CHEP) in 47 and cricohyoidopexy (CHP) in 3 cases showed that the number of SCL cases operated on within a year surpassed that of Total Laryngectomy after 2003. Selection criteria included performance status 0-1 and blood gas PO2>80 torr, especially in those patients over 70-years-old. Postoperative wound infection occurred in 16 patients (32%), with four requiring additional surgical intervention (two ruptured pexis and two chondritis induced by C3-C4 osteophytes). A history of radiotherapy and systemic complications, i.e., diabetes and renal failure, added to the risk of wound infection. Introducing a clinical pathway shortened hospitalization. Vocal function was achieved in 96% and swallowing function in 89% of patients. Five-year crude survival in CHEP was 69% and in TL 51%. Laryngeal preservation was 70%, increasing to 89% after the introduction of SCL. SCL-CHEP is thus indicated for unfavorable T2 (ASCO 2006), well-selected T3, T4, and rT1-4 (radiation failures). Effort should emphasize a good balance in prognosis and function in organ preservation for laryngeal cancer.

Supracricoid laryngectomy with cricohyoidoepiglotto-pexy or cricohyoido-pexy: Experience on 32 patients

OBJECTIVE

Supracricoid laryngectomy (SCL) with Cricohyoidoepiglotto-pexy (CHEP) or Cricohyoido-pexy (CHP) is an organ preservation surgery indicated for early and selected advanced laryngeal cancers. To verify the clinical usefulness of supracricoid laryngectomy versus total laryngectomy, a retrospective review was conducted.

METHODS

We summarized the clinical and postoperative data of 32 patients who received SCL over the past 9 years (1997-2005). Five-year survival rate of the SCL patient group (29 cases) was compared with that of the patient group receiving total laryngectomy (35 cases) within the same period.

RESULTS

Wound infection was detected in 12 patients (38%). Those with severe infection, which required surgical intervention, included two cases of ruptured pexis and two cases showing cricoid cartilage necrosis induced by Forestier disease. There were two T4 cases that resulted in extensive excision. In one case, excision involved the posterior part of the cricoid cartilage resulting in insufficient closure of the neoglottis; the patient received total laryngectomy 30 months after SCL-CHEP because of persistent aspiration of liquid diet. In the other T4 case, the tumor invaded the thyroid and arytenoid cartilages but not the cricoid cartilage. Reposition of the remaining corniculate cartilage resulted in sufficient closure of the neoglottis; this patient subsequently acquired satisfactory laryngeal function. The 5-year overall survival rate was 86% for SCL group and 61% for the total laryngectomy group (limited to Stages III and IV glottic cancers). The causes of the four deaths were distant metastasis, neck metastasis, and intercurrent disease, respectively. Two patients are alive with distant disease.

CONCLUSION

Through our experience in this series, the functional and oncological results of SCL showed certain advantages over those of total laryngectomy. Particularly, the clinical impact of SCL-CHEP was impressive; this technique needs is recommended to both head and neck surgeons and patients.

Electromyography of the cricoarytenoid unit during supracricoid laryngectomy with a cricohyoidoepiglottopexy procedure

Two patients who received supracricoid laryngectomy with cricohyoidoepiglottopexy to treat laryngeal cancers, underwent intra-operative electromyography analysis. After the lesion was removed and the electrodes were inserted into the remaining intrinsic laryngeal muscles, the depth of anaesthesia was carefully reduced. Gentle tactile stimulations were applied to the pharynx to trigger the reflex movement of the remaining arytenoids. Recordings were made when reflex movement was achieved.

Case one: Electromyography (EMG) of the remaining arytenoid demonstrated clear phase differences indicating reciprocal activities between the adductor group (lateral cricoarytenoid muscle, interarytenoid muscle) and the abductor muscle (posterior cricoarytenoid muscle). Case two: EMG of the remaining arytenoid demonstrated reciprocal activities between the interarytenoid muscle and the posterior cricoarytenoid muscle. Activity of the lateral cricoarytenoid muscle was not evident because the muscle was excised during removal of the paraglottic space. Mobility of the arytenoid was attributed to interaction between the interarytenoid muscle and posterior cricoarytenoid muscle. Reciprocal interaction between the interarytenoid muscle and posterior cricoarytenoid muscle alone is also capable of maintaining post-operative laryngeal functions after supracricoid laryngectomy with cricohyoidoepiglottopexy.

[Swallowing function after near-total laryngectomy, cricohyoidoepiglottopexy (CHEP), and cricohyoidopexy (CHP)]

We studied postoperative swallowing in 4 patients undergoing CHEP and 1 undergoing CHP. Swallowing was obtained by intense swallowing rehabilitation since only 1/4 of the larynx remained after near-total laryngectomy. Our swallowing rehabilitation program is detailed in this paper. The improvement of swallowing is classified into 3 stages. In stage I, volus directly intrudes into the trachea. In stage II, volus stagnates between laryngeal inlet and tracheal stoma. In stage III, volus directly flows through the esophageal inlet. Stage III indicates that rehabilitation is almost completed. Stage I is shortest at 2 to 14 days and Stage II longest at 7 to 80 days. The MTF (Method, Time, Food) score described by Fujimoto et al was used to analyze swallowing. Three cases following CHEP showed high scores shortly after the introduction of rehabilitation and reached the maximum score at discharge (15 points = normal swallowing). At present, these 3 patients are satisfied with swallowing and enjoy a good quality of life. In 2 other cases (1 CHEP and 1 CHP), both had a wide laryngeal inlet and still have some difficulty with liquids. Further modification of the surgical technique is needed especially for CHP.

Genetic code variations in mitochondria: tRNA as a major determinant of genetic code plasticity

Characteristic features of tRNA such as the anticodon sequence and modified nucleotides in the anticodon loop are thought to be crucial effectors for promoting or restricting codon reassignment. Our recent findings on basepairing rules between anticodon and codon in various metazoan mitochondria suggest that the complete loss of a codon is not necessarily essential for codon reassignment to take place. We postulate that a possible competition between two tRNAs with cognate anticodon sequences towards the relevant codon to be varied has a potential role in codon reassignment. Our proposition can be viewed as an expanded version of the codon capture theory proposed by Osawa and Jukes (J Mol Evol 28: 271-278, 1989).

An extra tRNAGly(U*CU) found in ascidian mitochondria responsible for decoding non-universal codons AGA/AGG as glycine

Amino acid assignments of metazoan mitochondrial codons AGA/AGG are known to vary among animal species; arginine in Cnidaria, serine in invertebrates and stop in vertebrates. We recently found that in the mitochondria of the ascidian Halocynthia roretzi these codons are exceptionally used for glycine, and postulated that they are probably decoded by a tRNA(UCU). In order to verify this notion unambig-uously, we determined the complete RNA sequence of the mitochondrial tRNA(UCU) presumed to decode codons AGA/AGG in the ascidian mitochondria, and found it to have an unidentified U derivative at the anticodon first position. We then identified the amino acids attached to the tRNA(U*CU), as well as to the conventional tRNAGly(UCC) with an unmodified U34, in vivo. The results clearly demonstrated that glycine was attached to both tRNAs. Since no other tRNA capable of decoding codons AGA/AGG has been found in the mitochondrial genome, it is most probable that this tRNA(U*CU) does actually translate codons AGA/AGG as glycine in vivo. Sequencing of tRNASer(GCU), which is thought to recognize only codons AGU/AGC, revealed that it has an unmodified guanosine at position 34, as is the case with vertebrate mitochondrial tRNASer(GCU) for codons AGA/AGG. It was thus concluded that in the ascidian, codons AGU/AGC are read as serine by tRNASer(GCU), whereas AGA/AGG are read as glycine by an extra tRNAGly(U*CU). The possible origin of this unorthodox genetic code is discussed.

Gene contents and organization of a mitochondrial DNA segment of the squid Loligo bleekeri

The nucleotide sequence of a 9240-base pair DNA fragment of the mitochondrial (mt) genome of a squid, Loligo bleekeri, was determined, in which 8 protein and 14 tRNA genes were identified. The gene organization of the mt-genome exhibits a greater resemblance to the gene organization of arthropods and a chiton, Katharina tunicata, than to those of a mussel, Mytilus edulis, and land snails. A cloverleaf-like structure was observed between the genes for subunits 4 and 5 of NADH dehydrogenase (ND4 and -5), which is considered to have originated from histidine tRNA. It is presumed that this structure functions as a transcriptional punctuation signal for the maturation of the ND4 and ND5 mRNAs.

The mitochondrial genome of the hemichordate Balanoglossus carnosus and the evolution of deuterostome mitochondria

The complete nucleotide sequence of the mitochondrial genome of the hemichordate Balanoglossus carnosus (acorn worm) was determined. The arrangement of the genes encoding 13 protein, 22 tRNA, and 2 rRNA genes is essentially the same as in vertebrates, indicating that the vertebrate and hemichordate mitochondrial gene arrangement is close to that of their common ancestor, and, thus, that it has been conserved for more than 600 million years, whereas that of echinoderms has been rearranged extensively. The genetic code of hemichordate mitochondria is similar to that of echinoderms in that ATA encodes isoleucine and AGA serine, whereas the codons AAA and AGG, whose amino acid assignments also differ between echinoderms and vertebrates, are absent from the B. carnosus mitochondrial genome. There are three noncoding regions of length 277, 41, and 32 bp: the larger one is likely to be equivalent to the control region of other deuterostomes, while the two others may contain transcriptional promoters for genes encoded on the minor coding strand. Phylogenetic trees estimated from the inferred protein sequences indicate that hemichordates are a sister group of echinoderms.

Ascidian mitochondrial tRNA(Met) possessing unique structural characteristics

Methionine tRNA was purified from muscle mitochondria of the ascidian Halocynthia roretzi and its RNA sequence was determined. Analysis of the nucleotide sequence revealed that unlike most metazoan mitochondrial tRNAs(Met), which have a highly conserved cytidine (C) or C-derivative at the wobble position, the H. roretzi mitochondrial tRNA(Met) possesses 5-carboxymethylaminomethyluridine (cmnm5U) at the first position of the anticodon. This is the first report of a single mitochondrial tRNA(Met) species having uridine (U) or a U-derivative at the wobble position.

RNA editing in metazoan mitochondria: staying fit without sex

RNA editing subsumes a number of functionally different mechanisms which have in common that they change the nucleotide sequence of RNA transcripts such that they become different from what would conventionally be predicted from their gene sequences. RNA editing has now been found in the organelles of numerous organisms as well as in a few nuclear transcripts. Most recently, it was shown to affect tRNAs in the mitochondria of several animals. The occurrence and evolutionary persistence of RNA editing is perplexing since backmutations in the genes might be assumed rapidly to eliminate the need for 'correction' of the gene sequences at the post-transcriptional level. Here, we review the recent RNA editing systems discovered in animal mitochondria and propose that they have arisen as a mechanism counteracting the accumulation of mutations that occurs in asexual genetic system.

Evolution of pulmonate gastropod mitochondrial genomes: comparisons of gene organizations of Euhadra, Cepaea and Albinaria and implications of unusual tRNA secondary structures

Complete gene organizations of the mitochondrial genomes of three pulmonate gastropods, Euhadra herklotsi, Cepaea nemoralis and Albinaria coerulea, permit comparisons of their gene organizations. Euhadra and Cepaea are classified in the same superfamily, Helicoidea, yet they show several differences in the order of tRNA and protein coding genes. Albinaria is distantly related to the other two genera but shares the same gene order in one part of its mitochondrial genome with Euhadra and in another part with Cepaea. Despite their small size (14.1-14.5 kbp), these snail mtDNAs encode 13 protein genes, two rRNA genes and at least 22 tRNA genes. These genomes exhibit several unusual or unique features compared to other published metazoan mitochondrial genomes, including those of other molluscs. Several tRNAs predicted from the DNA sequences possess bizarre structures lacking either the T stem or the D stem, similar to the situation seen in nematode mt-tRNAs. The acceptor stems of many tRNAs show a considerable number of mismatched basepairs, indicating that the RNA editing process recently demonstrated in Euhadra is widespread in the pulmonate gastropods. Strong selection acting on mitochondrial genomes of these animals would have resulted in frequent occurrence of the mismatched basepairs in regions of overlapping genes.

Polyadenylation creates the discriminator nucleotide of chicken mitochondrial tRNA(Tyr)

In the chicken mitochondrial genome, the gene for tRNA(Tyr) overlaps by one nucleotide with the downstream tRNA(Cys) gene, which is located on the same strand. The overlapping nucleotide, a guanosine residue, thus encodes both the discriminator base of the tRNA(Tyr) and the 5'base of the tRNA(Cys). When cDNA clones of circularized forms of the tRNA(Tyr) are analyzed, the discriminator nucleotide is an adenosine residue rather than the genomically encoded guanosine. Thus, the tRNA(Tyr) is subjected to an RNA editing activity similar to that shown to exist in the mitochondria of two other animal species. Interestingly, some cDNA clones have several adenosine residues at their 3'-ends instead of the expected CCA-sequence. Furthermore, a review of sequence data from animal mitochondrial genomes suggests that only tRNAs whose discriminator bases are adenosines tend to have genes that overlap with downstream genes. Thus, polyadenylation seems to be a major component of the RNA editing machinery that affects overlapping genes in animal mitochondria.

Transfer RNA editing in land snail mitochondria

Some mitochondrial tRNA genes of land snails show mismatches in the acceptor stems predicted from their gene sequences. The majority of these mismatches fall in regions where the tRNA genes overlap with adjacent downstream genes. We have synthesized cDNA from four circularized tRNAs and determined the sequences of the 5' and 3' parts of their acceptor stems. Three of the four tRNAs differ from their corresponding genes at a total of 13 positions, which all fall in the 3' part of the acceptor stems as well as the discriminator bases. The editing events detected involve changes from cytidine, thymidine, and guanosine to adenosine residues, which generally restore base-pairing in the stems. However, in one case an A-A mismatch is created from an A-C mismatch. It is suggested that this form of RNA editing may involve polyadenylylation of the maturing tRNAs as an intermediate.

Relationship among coelacanths, lungfishes, and tetrapods: a phylogenetic analysis based on mitochondrial cytochrome oxidase I gene sequences

To clarify the relationship among coelacanths, lungfishes, and tetrapods, the amino acid sequences deduced from the nucleotide sequences of mitochondrial cytochrome oxidase subunit I (COI) genes were compared. The phylogenetic tree of these animals, including the coelacanth Latimeria chalumnae and the lungfish Lepidosiren paradoxa, was inferred by several methods. These analyses consistently indicate a coelacanth/lungfish clade, to which little attention has been paid by previous authors with the exception of some morphologists. Overall evidence of other mitochondrial genes reported previously and the results of this study equally support the coelacanth/lungfish and lungfish/tetrapod clades, ruling out the coelacanth/tetrapod clade.

Codons AGA and AGG are read as glycine in ascidian mitochondria

A 1.2-kb DNA fragment of the cytochrome oxidase subunit I (CO I) gene of mitochondria isolated from an ascidian, Halocynthia roretzi, was amplified by polymerase chain reaction (PCR) and sequenced. Codons AGA and AGG appeared in its reading frame, indicating that these are sense codons in this organelle. Sequence comparisons with the corresponding regions of other animal mitochondrial CO I genes suggest that codons AGA and AGG correspond to glycine in the ascidian mitochondrial genome, but not to serine as in most invertebrate genomes, nor to stops as in vertebrate genomes. The other codons are identical to those of vertebrate mitochondria.