Hematopoietic stem cells (HSCs) exist in a dormant state and progressively lose regenerative potency as they undergo successive divisions. Why this functional decline occurs and how this information is encoded is unclear. To better understand how this information is stored, we performed RNA sequencing on HSC populations differing only in their divisional history. Comparative analysis revealed that genes upregulated with divisions are enriched for lineage genes and regulated by cell-cycle-associated transcription factors, suggesting that proliferation itself drives lineage priming. Downregulated genes are, however, associated with an HSC signature and targeted by the Polycomb Repressive Complex 2 (PRC2). The PRC2 catalytic subunits Ezh1 and Ezh2 promote and suppress the HSC state, respectively, and successive divisions cause a switch from Ezh1 to Ezh2 dominance. We propose that cell divisions drive lineage priming and Ezh2 accumulation, which represses HSC signature genes to consolidate information on divisional history into memory.

Transcription factor (TF)‐based reprogramming of somatic tissues holds great promise for regenerative medicine. Previously, we demonstrated that the TFs GATA2, GFI1B, and FOS convert mouse and human fibroblasts to hemogenic endothelial‐like precursors that generate hematopoietic stem progenitor (HSPC)‐like cells over time. This conversion is lacking in robustness both in yield and biological function. Herein, we show that inclusion of GFI1 to the reprogramming cocktail significantly expands the HSPC‐like population. AFT024 coculture imparts functional potential to these cells and allows quantification of stem cell frequency. Altogether, we demonstrate an improved human hemogenic induction protocol that could provide a valuable human in vitro model of hematopoiesis for disease modeling and a platform for cell‐based therapeutics. Database Gene expression data are available in the Gene Expression Omnibus (GEO) database under the accession number http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE130361.

The induction of hematopoiesis in various cell types via transcription factor (TF) reprogramming has been demonstrated by several strategies. The eventual goal of these approaches is to generate a product for unmet needs in hematopoietic cell transplantation therapies. The most successful strategies hew closely to clues provided from developmental hematopoiesis in terms of factor expression and environmental cues. In this review, we aim to summarize the TFs that play important roles in developmental hematopoiesis primarily and to also touch on adult hematopoiesis. Several aspects of cellular and molecular biology coalesce in this process, with TFs and surrounding cellular signals playing a major role in the overall development of the hematopoietic lineage. We attempt to put these elements into the context of reprogramming and highlight their roles.

Background Surgical decision making in gender-affirming mastectomy (GAM) is based on a patient's classification using the Fischer scale. Fischer 1 patients are excellent candidates for periareolar (PA) approach and Fischer 3 patients almost exclusively undergo double incision with free nipple grafting (DIFNG). Fischer 2 patients are in a gray zone in which decision making is more challenging. In this patient population, periareolar approaches can lead to increased complication and revision rates but free grafting procedures seem excessive. We have created a treatment algorithm to address Fischer 2 patients and additionally developed a novel technique, the batwing, to provide patients with more options. Methods A retrospective chart review was undertaken to analyze the Fischer classification of all patients undergoing top surgery by a single surgeon at an academic institution from 2014 to 2021. The choice of surgical technique used as well as the outcomes of GAM among Fischer 2 patients was analyzed. Results Four hundred four patients underwent GAM, and 51 (11%) had Fischer 2 classification. The surgical techniques used were PA (27%), batwing (39%), nipple-sparing double incision (NSDI, 24%), and DIFNG (10%). Of those, 10% had major complications and 20% requested revision for contour irregularities. Major complication rates for PA, batwing, NSDI, and DIFNG were as follows: 2 of 14 patients (14%), 1 of 20 patients (5%), 1 of 12 patients (8%), and 1 of 5 patients (20%), respectively. The revision rate by technique was PA (36%), batwing (15%), NSDI (17%), and DIFNG (0%). Conclusions For Fischer 2 patients, batwing and NSDI techniques avoid the need for free nipple graft while providing better exposure, improved control of nipple-areolar complex position, and decreased rate of revision as compared with the PA technique. The complication rate was not significantly different. We present an algorithm accounting for Fischer grade, unique patient characteristics, and patient desires.