Jared A. Blau

The Impact of Local Genome Sequence on Defining Heterochromatin Domains

Characterizing how genomic sequence interacts with trans-acting regulatory factors to implement a program of gene expression in eukaryotic organisms is critical to understanding genome function. One means by which patterns of gene expression are achieved is through the differential packaging of DNA into distinct types of chromatin. While chromatin state exerts a major influence on gene expression, the extent to which cis-acting DNA sequences contribute to the specification of chromatin state remains incompletely understood. To address this, we have used a fission yeast sequence element (L5), known to be sufficient to nucleate heterochromatin, to establish de novo heterochromatin domains in the Schizosaccharomyces pombe genome. The resulting heterochromatin domains were queried for the presence of H3K9 di-methylation and Swi6p, both hallmarks of heterochromatin, and for levels of gene expression. We describe a major effect of genomic sequences in determining the size and extent of such de novo heterochromatin domains. Heterochromatin spreading is antagonized by the presence of genes, in a manner that can occur independent of strength of transcription. Increasing the dosage of Swi6p results in increased heterochromatin proximal to the L5 element, but does not result in an expansion of the heterochromatin domain, suggesting that in this context genomic effects are dominant over trans effects. Finally, we show that the ratio of Swi6p to H3K9 di-methylation is sequence-dependent and correlates with the extent of gene repression. Taken together, these data demonstrate that the sequence content of a genomic region plays a significant role in shaping its response to encroaching heterochromatin and suggest a role of DNA sequence in specifying chromatin state.

Microvascular Anastomoses Using End-to-End versus End-to-Side Technique in Lower Extremity Free Tissue Transfer.

BACKGROUND The decision to perform an end-to-end (ETE) or end-to-side (ETS) arterial anastomosis in lower extremity free tissue transfer has not been thoroughly evaluated in a large multisurgeon setting. The authors compared the reconstructive outcomes of lower extremity free flaps with ETE and ETS arterial anastomoses. METHODS The authors retrospectively reviewed their 17-year institutional experience with lower extremity free flaps to determine whether ETE or ETS arterial anastomoses were associated with foot ischemic complications and flap failure. RESULTS From 1996 to 2013, 398 patients underwent 413 lower extremity free flaps with ETE (66%) or ETS (34%) arterial anastomoses. The incidence of postoperative foot ischemia was 2% (n = 8). The flap failure rate was 11% (n = 45). The ETS technique was preferred in patients with fewer intact vessels to the foot (32% ETS for three-vessel runoff, 36% ETS for two-vessel runoff, and 50% ETS for single-vessel runoff) and when an intact recipient vessel was selected for anastomosis (60% ETS for intact vessel vs. 25% ETS for distally occluded vessel). No differences were observed in the foot ischemia (p = 0.45) and flap failure rates (p = 0.59) for ETE versus ETS arterial anastomoses. In subset analyses, the incidence of foot ischemia did not differ for either technique in the context of impaired vascular runoff or recipient vessel selection. CONCLUSION No advantage was noted for ETE or ETS arterial anastomoses based on reconstructive outcomes. The choice of anastomotic technique in lower extremity free tissue transfer should be based on patient factors and the clinical circumstances encountered.

Delayed implant augmentation of breast free flaps.

BACKGROUND Two commonly used breast reconstruction techniques are (1) implant-based and (2) abdominal tissue-based procedures. When the two modalities are combined, the result is a unique construct that shares advantages and disadvantages of both approaches. Combining breast flaps and implants has been reported, yet the specific techniques associated with a reliable outcome remain unclear. MATERIALS AND METHODS Between July 2010 and 2014, a review of all patients who underwent delayed implant augmentation of a breast free flap reconstruction by the senior author was performed. Data were collected on patient characteristics, implants used, timing of reconstruction, and position of implant relative to the flap. RESULTS During the study period, 101 patients underwent breast reconstruction with 161 abdominal free flaps. Of these, 12 patients (12%) and 17 flaps (11%) had delayed implant augmentation. Of the 17 augmented flaps, 12 had expanders placed before final implant placement. Eleven implants were placed in the subflap position and 6 in the subpectoralis major position. The mean final implant size was 296.5 mL (range, 125-510 mL). At a mean follow-up of 17.1 months, there was one expander removed before complete expansion for impending extrusion and one silicone gel implant revision for malposition. CONCLUSION The results of delayed breast flap implant augmentation can be reliable and generate results that may not be obtainable with flaps or implants alone. Admittedly, the addition of an implant to a flap reconstruction exposes the patient to implant-related complications that would otherwise have been circumvented by a pure autologous reconstruction.