The distinct spatial architecture of the apical actin cables (or actin cap) facilitates rapid biophysical signaling between extracellular mechanical stimuli and intracellular responses, including nuclear shaping, cytoskeletal remodeling, and the mechanotransduction of external forces into biochemical signals. These functions are abrogated in lamin A/C-deficient mouse embryonic fibroblasts that recapitulate the defective nuclear organization of laminopathies, featuring disruption of the actin cap. However, how nuclear lamin A/C mediates the ability of the actin cap to regulate nuclear morphology remains unclear. Here, we show that lamin A/C expressing cells can form an actin cap to resist nuclear deformation in response to physiological mechanical stresses. This study reveals how the nuclear lamin A/C-mediated formation of the perinuclear apical actin cables protects the nuclear structural integrity from extracellular physical disturbances. Our findings highlight the role of the physical interactions between the cytoskeletal network and the nucleus in cellular mechanical homeostasis.

ResultsMyoD-iCre effects robust, muscle-specific inactivation of the Smn F7 allele. To investigate the cell-autonomous effects of depleting SMN in skeletal muscle, we began by testing which of 2 muscle Cre drivers, MyoD-iCre and Myf5-Cre (31, 32), was better suited for our studies. Each drives expression in muscle progenitor cells as early as E8 (33-35), and has been used to selectively deplete or restore disease-related proteins in skeletal muscle (27,36). To determine the tissue specificity of the 2 Cre lines, we separately bred the transgenic mice to animals harboring an inducible Smn deletion allele (Smn F7 ) bearing loxP sites on either side of exon 7 (37, 38). We then used PCR to examine which of the tissues of the double transgenics exhibited evidence of Cre-mediated recombination. As expected, we detected the presence of the deleted (Δ7) allele in the proximal and distal muscles of each of the double transgenic MyoD-iCre Smn F7 and Myf5-Cre Smn F7 animals ( Figure 1A). However, and consonant with other reports (27,39), whereas recombination of the Smn F7 allele was restricted to the skeletal muscle of the MyoD-iCre Smn F7 mice, it was also detected in the CNS tissue of the Myf5-Cre Smn F7 animals; the latter finding precluded the Myf5-Cre line for this study. We nevertheless proceeded to quantify the relative efficiency with which each of the Cre drivers effected Smn F7 inactivation in skeletal muscle. To directly measure how robustly each of the drivers converted the Smn F7 allele to the deleted Smn Δ7 form, we used Q-PCR on genomic DNA from the skeletal muscle of P7 MyoD-iCre Smn F7/+ and Myf5-Cre Smn F7/+ animals, and estimated relative levels of residual Smn F7 allele in each set of mutants. DNA from the muscle tissue of the MyoD-iCre Smn F7/+ mice contained lower levels of the Smn F7 allele than DNA from the muscle of Myf5-Cre Smn F7/+ mice ( Figure 1B), suggesting that MyoD-iCre is more robust in inactivating the floxed allele.As a second, indirect means of determining recombination efficiency, we established crosses to generate MyoD-iCre Smn F7/and Myf5-Cre Smn F7/mutants. In such mutants, the SMN protein

Traditionally, understanding differentiation pathway has been achieved by studying biochemical signal pathways controlled by various growth factors and cytokines. However, since various physical factors including tissue stiffness and topology can also determine the differentiation pathway of stem cells, mechanobiological pathway for controlling differentiation has been emphasized. Moreover, newly identified mechanobiological pathways have encouraged efforts to interpret stem cell differentiation in terms of cell-material interaction and provided clues to accurately design microenvironment of stem cells to control the direction of differentiation. Cells continuously recognize topographical and mechanical properties of the surrounding microenvironment and modulate their functional phenotypes through appropriate physiological responses to maintain homeostasis. Cell-cell and cell-extracellular matrix (ECM) interactions determine physical connections between the outside and the inside of individual cells to regulate various cellular functions, including adhesion, migration, proliferation, and cell differentiation. [3] Integrin, a transmembrane protein, is actively involved in outside-in and inside-out signaling mediated by polymerization and contraction of the cytoskeleton known to control cellular mechanotransduction pathways. [4] Therefore, a changed physical microenvironment can be detected by integrin-ECM interaction which has been traditionally considered as a primary target for controlling cell behavior through the material properties. Recent studies have shown that nuclear mechanosensation is a key process in response to physical stimuli. Nuclear membrane is tightly connected to integrin-based focal adhesion through cytoskeletal fibers that can transmit external force or cytoskeletal tension to the nuclear membrane, causing structural deformation of the nucleus. [5] Applied force not only changes nuclear shape, but also determines the conformation of many proteins located in nuclear membrane associated with various biochemical signals. [6] Since transcriptional regulatory mechanisms, such as histone modification and transcription factor activity, are controlled by force-mediated nuclear deformation, signal pathways for nuclear mechanosensation have been focused to interpret cellular adaptation mechanism including stem cell differentiation. [7] Various methods have been used to determine cell functions by changing cell adhesion through the corresponding changes in external substrates using micropatterned cell confinement, micro-/nanosized topographic substrates, and substrate stiffness. Micropatterning of ECM proteins is a well-established method to Recent findings about cell fate change induced by physical stimuli have expedited the discovery of underlying regulatory mechanisms that determine stem cell differentiation. Progress with regards to micro-/nanofabrication technology have led to the development of advanced materials that can mimic biophysical features of in vivo related circumstances of the human body...

PurposeManagement strategy in acute appendicitis patients initially presenting with abscess or mass is surrounded with controversy. This study was performed to identify the outcomes of management for this condition.MethodsWe retrospectively analyzed prospectively registered 76 patients (male:female = 39:37; mean age, 50.8 years) with appendicitis presenting with abscess or mass over a 9-year period at the Seoul National University Hospital. Patients were divided into three groups (emergency operation group, delayed operation group, and follow-up group), and clinical characteristics and outcomes of treatment were investigated.ResultsTwenty-eight patients (36.8%) underwent an emergency operation. Of the remaining 48 patients, 20 (41.7%) were initially treated with conservative management through the use of antibiotics only; the other 28 (58.3%) with and additional ultrasound-guided percutaneous drainage of the abscess. Twenty-six (54.2%) patients underwent planned operations after conservative management, and 22 (45.8%) were followed without surgery (median duration, 37.8 month), of which 3 (13%) underwent an appendectomy due to recurrent appendicitis (mean of 56.7 days after initial attack). There were no statistical differences in types of operation performed (appendectomy or ileocecectomy), postoperative complications, and postoperative hospital stay among the patients who underwent emergency operations, delayed operations and operations for recurrence during follow-up.ConclusionAlthough the recurrence rate was relatively low after conservative management for appendicitis patients presenting with abscess or mass, there was no difference in surgical outcome between the emergent, elective, or recurrent groups. Our results indicate that proper management of appendicitis with abscess or mass can be selected according to surgeon's preference.

Nuclear factor jB (NF-jB) is associated with the transcriptional activation of genes encoding chemokines, adhesion molecules, cytokines, and anti-apoptotic proteins, which are key components in immune responses and viral infection. Many viruses modulate NF-jB through numerous viral gene products to allow productive infections and immune escape. Here we report that herpes simplex virus-1 infected cell protein 27 (HSV-1 ICP27), an immediate early protein of HSV-1, represses NF-jB activity through binding to inhibitor of jB (IjBa), blocking phosphorylation and ubiquitination of IjBa, and stabilizing IjBa. These data may explain how NF-jB activity is regulated by ICP27 to escape immune responses during the very early period of HSV-1 infection.