Genome streamlining and clonal erosion in nutrient-limited environments: a test using genome-size variable populations.

Some selection-based theories propose that genome streamlining, favoring smaller genome sizes, is advantageous in nutritionally limited environments, particularly under P-limitation. To test this prediction, we conducted several experimental evolution trials on clonal populations of a facultatively asexual rotifer that exhibits intraspecific variation in genome size. Most trials showed a rapid decline in clonal diversity, which was accelerated in populations that were initially nonadapted. Populations consisting of three rotifer clones often became monoclonal within a few weeks, while populations starting with 120 clones eroded to 10 multilocus genotypes, of which only five were abundant in higher numbers. While P-limitation affected population growth during the experiments, it did not affect the outcome of clonal competition or the speed at which clonal diversity was lost. Common garden transplant experiments revealed that the evolved populations were better adapted to the experimental conditions than the ancestral controls. However, contrary to expectations, the evolved populations did not show an overrepresentation of small genomes. Intermediate genomes were also frequently abundant, although very large genomes were rare. Our findings suggest that fitness is more influenced by genotypic differences among clones than by differences in GS, and indicate that such differences might hinder genome streamlining during early adaptation to a new environment.

Massive expansion of sex-specific SNPs, transposon-related elements, and neocentromere formation shape the young W-chromosome from the mosquitofish Gambusia affinis.

BACKGROUND: The Western mosquitofish, Gambusia affinis, is a model for sex chromosome organization and evolution of female heterogamety. We previously identified a G. affinis female-specific marker, orthologous to the aminomethyl transferase (amt) gene of the related platyfish (Xiphophorus maculatus). Here, we have analyzed the structure and differentiation of the G. affinis W-chromosome, using a cytogenomics and bioinformatics approach. RESULTS: The long arm of the G. affinis W-chromosome (Wq) is highly enriched in dispersed repetitive sequences, but neither heterochromatic nor epigenetically silenced by hypermethylation. In line with this, Wq sequences are highly transcribed, including an active nucleolus organizing region (NOR). Female-specific SNPs and evolutionary young transposable elements were highly enriched and dispersed along the W-chromosome long arm, suggesting constrained recombination. Wq copy number expanded elements also include female-specific transcribed sequences from the amt locus with homology to TE. Collectively, the G. affinis W-chromosome is actively differentiating by sex-specific copy number expansion of transcribed TE-related elements, but not (yet) by extensive sequence divergence or gene decay. CONCLUSIONS: The G. affinis W-chromosome exhibits characteristic genomic properties of an evolutionary young sex chromosome. Strikingly, the observed sex-specific changes in the genomic landscape are confined to the W long arm, which is separated from the rest of the W-chromosome by a neocentromere acquired during sex chromosome evolution and may thus have become functionally insulated. In contrast, W short arm sequences were apparently shielded from repeat-driven differentiation, retained Z-chromosome like genomic features, and may have preserved pseudo-autosomal properties.

Linking genome size variation to population phenotypic variation within the rotifer, Brachionus asplanchnoidis.

Eukaryotic organisms usually contain much more genomic DNA than expected from their biological complexity. In explaining this pattern, selection-based hypotheses suggest that genome size evolves through selection acting on correlated life history traits, implicitly assuming the existence of phenotypic effects of (extra) genomic DNA that are independent of its information content. Here, we present conclusive evidence of such phenotypic effects within a well-mixed natural population that shows heritable variation in genome size. We found that genome size is positively correlated with body size, egg size, and embryonic development time in a population of the monogonont rotifer Brachionus asplanchnoidis. The effect on embryonic development time was mediated partly by an indirect effect (via egg size), and a direct effect, the latter indicating an increased replication cost of the larger amounts of DNA during mitosis. Our results suggest that selection-based change of genome size can operate in this population, provided it is strong enough to overcome drift or mutational change of genome size.

Surgical Treatment of Pyoderma Gangrenosum with Negative Pressure Wound Therapy and Skin Grafting, Including Xenografts: Personal Experience and Comprehensive Review on 161 Cases.

Significance: Pyoderma gangrenosum (PG) is a rare debilitating autoinflammatory ulcerative skin disease. No gold standard has been established for the treatment of PG. The role of surgical interventions and negative pressure wound therapy (NPWT) was discussed controversially until recently as these procedures might pose a trigger to further aggravate the condition. Recent Advances: Recent advances confirm the paradigm change that a surgical approach of PG with split thickness skin grafting (STSG) secured by NPWT is a safe and valuable treatment if performed under adequate immunosuppression. We elaborate this on the hand of a broad literature search retrieving 101 relevant articles describing 138 patients complemented with our personal experience on 23 patients, including 2 patients treated with a porcine xenodressing. Critical Issues: A wide range of surgical approaches have been reported, including xenografts. Treatment was finally successful in 86%, including the xenotransplant cases. Ten percent improved and failures were mainly reported without immunosuppression. Despite halting the inflammatory process, NPWT alone, without skin grafting, does not much accelerate healing time. The best surgical approach appears to be STSG fixed with NPWT as this leads to higher skin graft take. There remains the problem of the chronic nature of PG and the recurrence after tapering of immunosuppression or trauma; therefore, a sustained immunosuppressive treatment is suggested. Future Directions: While surgical treatment is supported by the published data, the exact immunosuppression is still evolving. Due to deeper insights into pathogenesis and growing clinical reports, a broader utilization of biologic treatments and a shift from tumor necrosis factor (TNF)-alpha to interleukin (IL)-12/23 or IL-23 antibodies alone are predictable, as IL-12/23 antibodies show good clinical responses with fewer side effects. The positive results with porcine xenodressings might be due to immunological effects of the xenomaterial; they appear promising, but are preliminary and should be confirmed in a larger patient collective.

Use of self-adherent silicone sheets in a pediatric burn patient: A case report and instructions for use.

Burns and scalds are relatively common injuries in children. Formation of hypertrophic scars or keloids is feared complications. A 2-year-old girl who spilled a cup of hot coffee onto herself developed widespread hypertrophic scars and beginning keloids on her upper chest, despite application of pressure garments and daily massage with silicone gel. Herein, we describe instructions for use of prolonged continuous 24-hour occlusive application of self-adherent silicone sheets to help mitigate the formation of scar tissue.

Within-Population Genome Size Variation is Mediated by Multiple Genomic Elements That Segregate Independently during Meiosis.

Within-species variation in genome size has been documented in many animals and plants. Despite its importance for understanding eukaryotic genome diversity, there is only sparse knowledge about how individual-level processes mediate genome size variation in populations. Here, we study a natural population of the rotifer Brachionus asplanchnoidis whose members differ up to 1.9-fold in diploid genome size, but were still able to interbreed and produce viable offspring. We show that genome size is highly heritable and can be artificially selected up or down, but not below a certain basal diploid genome size for this species. Analyses of segregation patterns in haploid males reveal that large genomic elements (several megabases in size) provide the substrate of genome size variation. These elements, and their segregation patterns, explain the generation of new genome size variants, the short-term evolutionary potential of genome size change in populations, and some seemingly paradoxical patterns, like an increase in genome size variation among highly inbred lines. Our study suggests that a conceptual model involving only two variables, 1) a basal genome size of the population, and 2) a vector containing information on additional elements that may increase genome size in this population (size, number, and meiotic segregation behavior), can effectively address most scenarios of short-term evolutionary change of genome size in a population.

Do genome size differences within Brachionus asplanchnoidis (Rotifera, Monogononta) cause reproductive barriers among geographic populations?

Genome size in the rotifer Brachionus asplanchnoidis, which belongs to the B. plicatilis species complex, is greatly enlarged and extremely variable (205-407 Mbp). Such variation raises the question whether large genome size differences among individuals might cause reproductive barriers, which could trigger speciation within this group by restricting gene flow across populations. To test this hypothesis, we used B. asplanchnoidis clones from three geographic populations and conducted assays to quantify reproductive isolation among clones differing in genome size, and we examined the population structure of all three populations using amplified fragment length polymorphisms (AFLPs). AFLPs indicated that these populations were genetically separated, but we also found hints of natural gene flow. Clones from different populations with genome size differences of up to 1.7-fold could interbred successfully in the laboratory and give rise to viable, fertile 'hybrid' offspring. Genome sizes of these 'hybrids' were intermediate between those of their parents, and fitness in terms of male production, population growth, and egg development time was not negatively affected. Thus, we found no evidence for reproductive isolation or nascent speciation within B. asplanchnoidis. Instead, our results suggest that gene flow within this species can occur despite a remarkably large range of genome sizes.

Misdiagnosed microcystic adnexal carcinoma on the lateral forehead and challenges in reconstruction of a large and bone-deep defect.

BACKGROUND: Microcystic adnexal carcinoma (MAC) is a rare cutaneous malignancy characterized by aggressive local infiltration, including a high propensity for perineural invasion. Histologically it can be easily confused with benign adnexal tumors, which often leads to inappropriate initial treatment. As a consequence delayed surgical excision often requires removal of large cutaneous masses which can be followed by challenges in reconstruction. METHODS: We report the case of a challenging reconstruction of a large forehead defect by a modified AT flap with central Burow's triangle grafting and previous wound conditioning using hyaluronic acid after complete micrographic removal of MAC. RESULTS: A 80-year-old healthy female presented with an almost six year history of an asymptomatic slowly progressing skin mass previously biopsied and diagnosed as benign syringoma five years in advance. Deep biopsies confirmed MAC. She underwent staged surgical excision with Tübingen torte technique with removal of the frontal periostium. A skin substitute of esterified hyaluronic acid was applied for three weeks to the bone-deep 6 × 7 cm defect leading to good granulation tissue above the bone. Final reconstruction was achieved by an AT flap combined with full thickness skin transplantation of the central dog ear. The cosmetic outcome was satisfactory, no recurrence was observed within 18 months follow-up. CONCLUSIONS: We confirm the histological difficulties in the diagnosis of this tumor entity and the large extension of MAC due to delay in diagnosis and treatment. Deep tumor removal including the periostium might be necessary to achieve tumor free margins. Fast granulation tissue above the frontal bone might be achieved by applying hyaluronic acid products. The combination an AT flap with transplantation of the adjacent Burow's triangles gives optimal skin texture and color matching and seems to be a good option to close even large defects of the front especially for supra brow defects.

A transcriptome derived female-specific marker from the invasive Western mosquitofish (Gambusia affinis).

Sex-specific markers are a prerequisite for understanding reproductive biology, genetic factors involved in sex differences, mechanisms of sex determination, and ultimately the evolution of sex chromosomes. The Western mosquitofish, Gambusia affinis, may be considered a model species for sex-chromosome evolution, as it displays female heterogamety (ZW/ZZ), and is also ecologically interesting as a worldwide invasive species. Here, de novo RNA-sequencing on the gonads of sexually mature G. affinis was used to identify contigs that were highly transcribed in females but not in males (i.e., transcripts with ovary-specific expression). Subsequently, 129 primer pairs spanning 79 contigs were tested by PCR to identify sex-specific transcripts. Of those primer pairs, one female-specific DNA marker was identified, Sanger sequenced and subsequently validated in 115 fish. Sequence analyses revealed a high similarity between the identified sex-specific marker and the 3´ UTR of the aminomethyl transferase (amt) gene of the closely related platyfish (Xiphophorus maculatus). This is the first time that RNA-seq has been used to successfully characterize a sex-specific marker in a fish species in the absence of a genome map. Additionally, the identified sex-specific marker represents one of only a handful of such markers in fishes.

Reconstruction of large rectangular infraorbital and malar skin defects in elderly patients with a modified "reading man flap" using local tumescent anesthesia.

BACKGROUND: The classical "reading man flap" is a recently described flap named after its appearance and mainly used for reconstruction of circular malar or infraorbital skin defects. It avoids surgical complications such as lower lid retraction and ectropion but is limited to circular skin defects. Local tumescent anesthesia uses a diluted local anesthetic together with diluted epinephrine to anesthetize large skin areas without the need for general anesthesia. OBJECTIVES: To assess the esthetic outcome, pain control, and complications of a modified "reading man flap" under local tumescent anesthesia in elderly patients with rectangular malar or periorbital skin defects. METHODS: Two flaps are used to close the surgical defect, the first rectangular flap is transposed to the defect area, then approximately half to two-thirds of the flap's donor site are closed directly as done with transposition flaps, whereas a second smaller triangular flap is advanced for the closure of the last third of the remaining now triangular donor site, where the greatest tension would occur if closed directly. RESULTS: The median age of patients was 83 years (range 64-92 years) of the total 12 patients, 10 (83%) were women, and two were men. The mean defect size was 9.2 cm(2) (5.5-22.1 cm(2) ). The defect closure was possible in all patients, no lasting postoperative complications occurred, and cosmetic results were satisfactory. Twenty to 70 ml of local tumescent anesthesia were used, and a larger volume (≥ 40 ml) was associated with better pain control (P = 0.03). CONCLUSIONS: The modified "reading man flap" is a good option for the closure of larger rectangular facial skin defects especially in elderly patients, and the use of at least 40 ml of tumescent solution is suggested to achieve optimal pain control.

Using the Peng flap for a wide dorsal nasal defect.

Reconstructions of large surgical defects of the central part of the nose pose a challenge for the surgeon due to its cosmetically prominent location. Treatment options include second intention healing, full-thickness skin grafts and various local flaps. In the present case the "Peng flap" was used for the reconstruction of a 3.1 × 7 cm sized deep defect of the convex curve of the central nasal area in a 66-year-old woman. The Peng flap was performed as single-stage procedure without complications. Good cosmetic outcome was provided by the use of adjacent skin from the lax perinasal area, the placement of the scar lines between facial cosmetic units, and the excellent tissue match for the sebaceous nasal skin. Considering the few complications of a single-stage procedure associated with an excellent aesthetic outcome, the Peng flap should be considered not only as an effective choice for reconstruction of the cosmetically complex midline nasal tip but also the convex curve of the central nose.