Early Masseter to Facial Nerve Transfer May Improve Smile Excursion in Facial Paralysis.

BACKGROUND: Masseter-to-facial nerve transfer has been shown to be an effective and safe treatment option in patients with acute and subacute facial palsy. The present article aims to characterize whether there is a benefit in early nerve transfers while minimizing other confounding variables; we present a study that consist of only patients with complete facial nerve paralysis resulting from intratemporal facial nerve resections. METHODS: Between 2012 and 2016, 7 masseter-to-facial nerve transfers were performed for complete facial nerve palsy after intratemporal proximal nerve resections. Pre- and postoperative photographic and video evaluations were performed using both the Sunnybrook facial grading scale and the MEEI FACE-gram software for more objective metric measurements. Statistical analysis was performed to determine which patient and surgical variables had significant effects on outcome. RESULTS: Mean 14-month follow-up revealed that patients who underwent nerve transfer prior to 6 months' denervation achieved postoperative oral commissural excursion of 11.1 mm versus 6.5 mm in patients who underwent nerve transfer after 6 months (P = 0.003). Performing masseter-to-facial nerve transfer to the main facial nerve trunk resulted in a significantly higher improvement in the modiolus-philtral ratio (31.6% versus 6.1%) than selective transfer in patients (P = 0.01) at the latest follow-up. CONCLUSIONS: Early masseter-to-facial nerve transfers, before 6 months of palsy duration, can potentially improve smile excursion and symmetry of open mouth smile. Additionally, truncal coaptations may provide improved tone over coapting to selective facial nerve branches. These findings necessitate larger studies regarding the importance of denervation time with fifth-to-seventh nerve transfers.

Histone modifications at human enhancers reflect global cell-type-specific gene expression.

The human body is composed of diverse cell types with distinct functions. Although it is known that lineage specification depends on cell-specific gene expression, which in turn is driven by promoters, enhancers, insulators and other cis-regulatory DNA sequences for each gene, the relative roles of these regulatory elements in this process are not clear. We have previously developed a chromatin-immunoprecipitation-based microarray method (ChIP-chip) to locate promoters, enhancers and insulators in the human genome. Here we use the same approach to identify these elements in multiple cell types and investigate their roles in cell-type-specific gene expression. We observed that the chromatin state at promoters and CTCF-binding at insulators is largely invariant across diverse cell types. In contrast, enhancers are marked with highly cell-type-specific histone modification patterns, strongly correlate to cell-type-specific gene expression programs on a global scale, and are functionally active in a cell-type-specific manner. Our results define over 55,000 potential transcriptional enhancers in the human genome, significantly expanding the current catalogue of human enhancers and highlighting the role of these elements in cell-type-specific gene expression.

Distinct and predictive chromatin signatures of transcriptional promoters and enhancers in the human genome.

Eukaryotic gene transcription is accompanied by acetylation and methylation of nucleosomes near promoters, but the locations and roles of histone modifications elsewhere in the genome remain unclear. We determined the chromatin modification states in high resolution along 30 Mb of the human genome and found that active promoters are marked by trimethylation of Lys4 of histone H3 (H3K4), whereas enhancers are marked by monomethylation, but not trimethylation, of H3K4. We developed computational algorithms using these distinct chromatin signatures to identify new regulatory elements, predicting over 200 promoters and 400 enhancers within the 30-Mb region. This approach accurately predicted the location and function of independently identified regulatory elements with high sensitivity and specificity and uncovered a novel functional enhancer for the carnitine transporter SLC22A5 (OCTN2). Our results give insight into the connections between chromatin modifications and transcriptional regulatory activity and provide a new tool for the functional annotation of the human genome.