GTPase activity regulates FtsZ ring positioning in Caulobacter crescentus.

Bacterial cell division is crucial for replication and requires careful coordination via proteins collectively called the divisome. The tubulin-like GTPase FtsZ is the master regulator of this process and serves to recruit downstream divisome proteins and regulate their activities. Upon assembling at mid-cell, FtsZ exhibits treadmilling motion driven by GTP binding and hydrolysis. Treadmilling is proposed to play roles in Z-ring condensation and in distribution and regulation of peptidoglycan (PG) cell wall enzymes. FtsZ polymer superstructure and dynamics are central to its function, yet their regulation is incompletely understood. We addressed these gaps in knowledge by evaluating the contribution of GTPase activity to FtsZ's function in vitro and in Caulobacter crescentus cells. We observed that a lethal mutation that abrogates FtsZ GTP hydrolysis impacts FtsZ dynamics and Z-ring positioning, but not constriction. Aberrant Z-ring positioning was due to insensitivity to the FtsZ regulator MipZ when GTPase activity is reduced. Z-ring mislocalization resulted in DNA damage, likely due to constriction over the nucleoid. Collectively, our results indicate that GTP hydrolysis serves primarily to position the Z-ring at mid-cell in Caulobacter. Proper Z-ring localization is required for effective coordination with chromosome segregation to prevent DNA damage and ensure successful cell division.

Integration of cell wall synthesis and chromosome segregation during cell division in Caulobacter.

To divide, bacteria must synthesize their peptidoglycan (PG) cell wall, a protective meshwork that maintains cell shape. FtsZ, a tubulin homolog, dynamically assembles into a midcell band, recruiting division proteins, including the PG synthases FtsW and FtsI. FtsWI are activated to synthesize PG and drive constriction at the appropriate time and place. However, their activation pathway remains unresolved. In Caulobacter crescentus, FtsWI activity requires FzlA, an essential FtsZ-binding protein. Through time-lapse imaging and single-molecule tracking of Caulobacter FtsW and FzlA, we demonstrate that FzlA is a limiting constriction activation factor that signals to promote conversion of inactive FtsW to an active, slow-moving state. We find that FzlA interacts with the DNA translocase FtsK and place FtsK genetically in a pathway with FzlA and FtsWI. Misregulation of the FzlA-FtsK-FtsWI pathway leads to heightened DNA damage and cell death. We propose that FzlA integrates the FtsZ ring, chromosome segregation, and PG synthesis to ensure robust and timely constriction during Caulobacter division.

Surgical Resection of Colorectal Liver Metastases: Attitudes and Practice Patterns in the Deep South.

BACKGROUND: Metastatic disease is the leading cause of mortality in colorectal cancer. Resection of colorectal liver metastases, when possible, is associated with improved long-term survival and the possibility of cure. However, nationwide studies suggest that liver resection is under-utilized in the treatment of colorectal liver metastases. This study was undertaken to understand attitudes and practice patterns among medical oncologists in the Deep South. METHODS: A survey of medical oncologists in the states of Alabama, Mississippi, and the Florida panhandle was performed. Respondents were queried regarding perceptions of resectability and attitudes towards surgical referral. RESULTS: We received 63 responses (32% response rate). Fifty percent of respondents reported no liver surgeons in their practice area. Commonly perceived contraindications to liver resection included extrahepatic metastatic disease (72%), presence of > 4 metastases (72%), bilobar metastases (61%), and metastases > 5 cm (46%). Bilobar metastatic disease was perceived as a contraindication more frequently by non-academic medical oncologists (70% vs. 33%, p = 0.03). CONCLUSIONS: Wide variations exist in perceptions of resectability and referral patterns for colorectal liver metastases among surveyed medical oncologists. There is a need for wider dissemination of resectability criteria and more liver surgeon involvement in the management of patients with colorectal liver metastases.

Functional Disorders of Constipation: Paradoxical Puborectalis Contraction and Increased Perineal Descent.

Paradoxical puborectalis contraction (PPC) and increased perineal descent (IPD) are subclasses of obstructive defecation. Often these conditions coexist, which can make the evaluation, workup, and treatment difficult. After a thorough history and examination, workup begins with utilization of proven diagnostic modalities such as cinedefecography and anal manometry. Advancements in technology have increased the surgeon's diagnostic armamentarium. Biofeedback and pelvic floor therapy have proven efficacy for both conditions as first-line treatment. In circumstances where PPC is refractory to biofeedback therapy, botulinum toxin injection is recommended. Historically, pelvic floor repair has been met with suboptimal results. In IPD, surgical therapy now is directed toward the potentially attendant abnormalities such as rectoanal intussusception and rectal prolapse. When these associated abnormalities are not present, an ostomy should be considered in patients with IPD as well as medically refractory PPC.