Complete mitochondrial genomes of the human follicle mites Demodex brevis and D. folliculorum: novel gene arrangement, truncated tRNA genes, and ancient divergence between species

Background

Follicle mites of the genus Demodex are found on a wide diversity of mammals, including humans; surprisingly little is known, however, about the evolution of this association. Additional sequence information promises to facilitate studies of Demodex variation within and between host species. Here we report the complete mitochondrial genome sequences of two species of Demodex known to live on humans—Demodex brevis and D. folliculorum—which are the first such genomes available for any member of the genus. We analyzed these sequences to gain insight into the evolution of mitochondrial genomes within the Acariformes. We also used relaxed molecular clock analyses, based on alignments of mitochondrial proteins, to estimate the time of divergence between these two species.

Results

Both Demodex genomes shared a novel gene order that differs substantially from the ancestral chelicerate pattern, with transfer RNA (tRNA) genes apparently having moved much more often than other genes. Mitochondrial tRNA genes of both species were unusually short, with most of them unable to encode tRNAs that could fold into the canonical cloverleaf structure; indeed, several examples lacked both D- and T-arms. Finally, the high level of sequence divergence observed between these species suggests that these two lineages last shared a common ancestor no more recently than about 87 mya.

Conclusions

Among Acariformes, rearrangements involving tRNA genes tend to occur much more often than those involving other genes. The truncated tRNA genes observed in both Demodex species would seem to require the evolution of extensive tRNA editing capabilities and/or coevolved interacting factors. The molecular machinery necessary for these unusual tRNAs to function might provide an avenue for developing treatments of skin disorders caused by Demodex. The deep divergence time estimated between these two species sets a lower bound on the time that Demodex have been coevolving with their mammalian hosts, and supports the hypothesis that there was an early split within the genus Demodex into species that dwell in different skin microhabitats.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1124) contains supplementary material, which is available to authorized users.

Disappearance of well-differentiated carcinoma of the prostate: effect of transurethral resection of the prostate, prostate-specific antigen, and prostate biopsy

OBJECTIVES

To characterize the effect of prostate-specific antigen (PSA) and transurethral resection of the prostate (TURP) on the rate of diagnosis of well-differentiated (WD) prostate cancer (PCa) and PCa mortality.

METHODS

All cases of PCa and rates of TURP at both Wilford Hall and Brooke Army Medical Centers between 1984 and 1995 were reviewed. Tumor grade was compared between prostate needle biopsy and TURP. The pattern of diagnosis was analyzed annually and for two time periods: pre-PSA (1984 to 1988) and post-PSA (1989 to 1995).

RESULTS

The number of WD tumors fell by 50% over the period of study and was caused by a fall in number of TURPs as well as in WD tumors detected by TURP. PSA for early detection of PCa began in 1988, and within 5 years a more than 50% fall in the rate of metastatic disease was witnessed. These two events (PSA screening and fall in TURPs) led to an increase from 57% to 92% of tumors that were both clinically significant and potentially curable.

CONCLUSIONS

These data help explain the fall in the rate of diagnosis of WD PCa. The resultant increase in the diagnosis of moderately and poorly differentiated PCa, coupled with the dramatic fall in the rate of diagnosis of metastatic PCa, may explain the reports of a fall in PCa mortality. If this observation is replicated in other populations, it may provide further impetus for a stronger recommendation for early detection with PSA and digital rectal examination.

The relationship between early biochemical failure and perineural invasion in pathological T2 prostate cancer

OBJECTIVES

To evaluate, in patients with pathologically localized prostate cancer, the relationship between early biochemical failure, i.e. an increasing prostate-specific antigen (PSA) level, and perineural invasion (PNI) on final pathology.

PATIENTS AND METHODS

The records were reviewed of 171 patients with prostate cancer who underwent prostatectomy at one institution between January 1992 and December 1995. Data on the histology, therapy and PSA level were collected and evaluated.

RESULTS

Of the 171 patients with pathologically localized (pT2) prostate cancer, 131 were evaluable; 17 (13%) had a detectable PSA level in the first 5 years after surgery and 63 had PNI in the pathological specimen. Of those with PSA recurrence, 14 had PNI, one had no PNI and in two there was no comment on PNI. In comparison, only 10 of the 17 patients with recurrence had a Gleason sum of >/= 7.

CONCLUSION

Perineural invasion seems to be an important predictor of early outcome in patients with organ-confined prostate cancer treated by prostatectomy. In this series it was the most sensitive predictor of biochemical failure. A more detailed pathological evaluation of prostate cancer may allow the clinician to provide closer surveillance and better informed clinical decision-making.

Crystallization and preliminary diffraction analysis of porcine heart mitochondrial NADP+-dependent isocitrate dehydrogenase

Isocitrate dehydrogenases [isocitrate:NAD(P)(+) oxidoreductase (decarboxylating), E.C. 1.1.1.42] are ubiquitous metabolic enzymes which occur in all living organisms. The NADP(+)- dependent mitochondrial isocitrate dehydrogenase from pig heart has been crystallized from polyethylene glycol/sodium sulfate mixtures in the presence of Mg(2+) and isocitrate. The crystals belong to space group C2 with a = 137.0, b = 113.4, c = 65.0 A and beta = 98.5 degrees, and diffract to at least 2.4 A resolution. There are two protein monomers per asymmetric unit which are related by non-crystallographic twofold symmetry.

The primary structure of carboxypeptidase S1 from Penicillium janthinellum

The complete amino acid sequence of carboxypeptidase S1 from Penicillium janthinellium has been determined by N-terminal sequencing of the reduced and vinylpyridinated protein and of peptides obtained by cleaved with cyanogen bromide, iodosobenzoic acid, hydroxylamine, endoproteinase LysC, endoproteinase AspN and Glu-specific proteinase from B. licheniformis. The enzyme consists of a single peptide chain of 433 amino acid residues and contains 9 half-cystine residues and one glycosylated asparagine residue. A comparison to other carboxypeptidases shows that the enzyme is homologous to carboxypeptidase-Y and carboxypeptidase-MIII from malt. Specificity and binding of substrates are discussed from a three-dimensional model based on the known structure of carboxypeptidase-Y from Saccharomyces cereviciae and carboxypeptidase II from wheat.

Composition and activity of the photosynthetic apparatus in temperature-sensitive mutants of higher plants

Six nuclear mutants of corn, six of soybean, and seven of cotton displayed low temperature-induced virescence when grown in controlled environments. For the group of plants studied, an increase in leaf chlorophyll a/b ratio was correlated with a temperature-sensitive biosynthetic sequence leading to a reduction in total chlorophyll content. These pigment alterations were reflected in the composition and quantity of the two major chlorophyll-protein complexes of chloroplast membranes. Changes in the amount of the major light-harvesting chlorophyll-protein complex was a prime consequence of the nuclear mutations. A decrease in the light-harvesting chlorophyll component of the light reaction centers of the leaf may account for the decrease in size of the photo-synthetic unit frequently noted in chlorophyll-deficient mutants. Variations in the concentration of the chlorophyll-protein complexes in the chloroplast lamellae may be causally related to variations in CO(2) compensation points of mutant soybean and cotton plants.