Cells have evolved sophisticated systems that integrate internal and external inputs to coordinate cell shape changes during processes, such as development, cell identity determination, and cell and tissue homeostasis. Cellular shape-change events are driven by the mechanobiome, the network of macromolecules that allows cells to generate, sense and respond to externally imposed and internally generated forces. Together, these components build the cellular contractility network, which is governed by a control system. Proteins, such as non-muscle myosin II, function as both sensors and actuators, which then link to scaffolding proteins, transcription factors and metabolic proteins to create feedback loops that generate the foundational mechanical properties of the cell and modulate cellular behaviors. In this Review, we highlight proteins that establish and maintain the setpoint, or baseline, for the control system and explore the feedback loops that integrate different cellular processes with cell mechanics. Uncovering the genetic, biophysical and biochemical interactions between these molecular components allows us to apply concepts from control theory to provide a systems-level understanding of cellular processes. Importantly, the actomyosin network has emerged as more than simply a 'downstream' effector of linear signaling pathways. Instead, it is also a significant driver of cellular processes traditionally considered to be 'upstream'.

Summary A reliable serological marker of acute cellular rejection (ACR) after small bowel transplantation (SBTx) is still missing. Plasma citrulline level (PCL) reflects the functional integrity of intestinal mucosa which is partially lost during ACR. The aim of our study was to investigate the role of PCL as marker of ACR after SBTx. Eighteen German landrace pigs were used and divided into three groups. Group 1 (G1), autologous SBTx (n = 4) as control; group 2 (G2), allogeneic SBTx without immunosuppression (IS) (n = 7) and group 3 (G3), allogeneic SBTx with IS (n = 7). IS consisted of tacrolimus and steroids without induction treatment. Observation period was 14 days. Mucosal biopsies were obtained intraoperatively and daily using a Thiry–Vella loop. ACR was differentiated into indeterminate, mild, moderate and severe using a standardized grading schema. PCL was measured daily. An ACR onset occurred generally from postoperative day 4 both in G2 and G3 as mild form and developed differently in the two groups: moderate to severe in G2 and indeterminate to mild in G3. A significant decline of PCL occurred only in cases of moderate and severe ACR, but not in cases of indeterminate and mild ACR. The PCL failed as a marker in the early diagnosis of ACR and became reliable only when advanced mucosal damage was present.

No abstract