Spectrum and Relevance of Incidental Bowel Findings on Computed Tomography.

A wide spectrum of incidental bowel findings can be seen on CT, including but not limited to, pneumatosis intestinalis, diverticular disease, non-obstructive bowel dilatation, transient small bowel intussusception, and submucosal fat. Radiologists should be aware that such findings are almost always benign and of little clinical significance in the absence of associated symptoms. Conversely, vigilance must be maintained when evaluating the bowel, because malignant neoplasms occasionally come to clinical attention as incidental imaging findings. When suspicious incidental bowel wall thickening is detected, the radiologist can alert the clinical team to the finding prior to the patient becoming symptomatic, potentially leading to definitive management at an early, more curable stage.

The utility of abdominopelvic CT in pregnant patients with abdominal pain and a negative or inconclusive abdominal MRI.

Pregnant women with abdominal pain can pose a diagnostic dilemma due to the nonspecific nature of symptoms and the desire to avoid radiation to the conceptus. Many algorithms will suggest ultrasound (US) or Magnetic Resonance Imaging (MRI) as the first-line imaging choice in pregnant women with abdominal pain due to the lack of ionizing radiation. However, these studies can have limitations as well. Abdominopelvic MRI is susceptible to respiratory motion that could cause a study to be nondiagnostic (Zaitsev et al., 2015 [1]). In the current case series, we present 8 pregnant patients with abdominal pain who underwent CT abdomen and pelvis after negative or inconclusive abdominal MRI exams. To our knowledge, this is the only case series that describes CT findings in the pregnant population after negative or inconclusive MRI.

Tropomodulin binds two tropomyosins: a novel model for actin filament capping.

Tropomodulin, a tropomyosin-binding protein, caps the slow-growing (pointed) end of the actin filament regulating its dynamics. Tropomodulin, therefore, is important for determining cell morphology, cell movement, and muscle contraction. For the first time we show that one tropomodulin molecule simultaneously binds two tropomyosin molecules in a cooperative manner. On the basis of the tropomodulin solution structure and predicted secondary structure, we introduced a series of point mutations in regions important for tropomyosin binding and actin capping. Capping activity of these mutants was assayed by measuring actin polymerization using pyrene fluorescence. Using direct methods (circular dichroism and native gel electrophoresis) for detecting tropomodulin/tropomyosin binding, we localized the second tropomyosin-binding site to residues 109-144. Despite previous reports that the second binding site is for erythrocyte tropomyosin only, we found that both short nonmuscle and long muscle alpha-tropomyosins bind there as well, though with different affinities. We propose a model for actin capping where one tropomodulin molecule can bind to two tropomyosin molecules at the pointed end.

Structural requirements of tropomodulin for tropomyosin binding and actin filament capping.

Regulation of actin filament dynamics underlies many cellular functions. Tropomodulin together with tropomyosin can cap the pointed, slowly polymerizing, filament end, inhibiting addition or loss of actin monomers. Tropomodulin has an unstructured N-terminal region that binds tropomyosin and a folded C-terminal domain with six leucine-rich repeats. Of tropomodulin 1's 359 amino acids, an N-terminal fragment (Tmod1(1)(-)(92)) suffices for in vitro function, even though the C-terminal domain can weakly cap filaments independent of tropomyosin. Except for one short alpha-helix with coiled coil propensity (residues 24-35), the Tmod1(1)(-)(92) solution structure shows that the fragment is disordered and highly flexible. On the basis of the solution structure and predicted secondary structure, we have introduced a series of mutations to determine the structural requirements for tropomyosin binding (using native gels and CD) and filament capping (by measuring actin polymerization using pyrene fluorescence). Tmod1(1)(-)(92) fragments with mutations of an interface hydrophobic residue, L27G and L27E, designed to destroy the alpha-helix or coiled coil propensity, lost binding ability to tropomyosin but retained partial capping function in the presence of tropomyosin. Replacement of a flexible region with alpha-helical residues (residues 59-61 mutated to Ala) had no effect on tropomyosin binding but inhibited the capping function. A mutation in a region predicted to be an amphipathic helix (residues 65-75), L71D, destroyed the capping function. The results suggest that molecular flexibility and binding to actin via an amphipathic helix are both required for tropomyosin-dependent capping of the pointed end of the actin filament.