Investigating cellular and molecular mechanisms of neurogenesis in Capitella teleta sheds light on the ancestor of Annelida.

BACKGROUND: Diverse architectures of nervous systems (NSs) such as a plexus in cnidarians or a more centralized nervous system (CNS) in insects and vertebrates are present across Metazoa, but it is unclear what selection pressures drove evolution and diversification of NSs. One underlying aspect of this diversity lies in the cellular and molecular mechanisms driving neurogenesis, i.e. generation of neurons from neural precursor cells (NPCs). In cnidarians, vertebrates, and arthropods, homologs of SoxB and bHLH proneural genes control different steps of neurogenesis, suggesting that some neurogenic mechanisms may be conserved. However, data are lacking for spiralian taxa. RESULTS: To that end, we characterized NPCs and their daughters at different stages of neurogenesis in the spiralian annelid Capitella teleta. We assessed cellular division patterns in the neuroectoderm using static and pulse-chase labeling with thymidine analogs (EdU and BrdU), which enabled identification of NPCs that underwent multiple rounds of division. Actively-dividing brain NPCs were found to be apically-localized, whereas actively-dividing NPCs for the ventral nerve cord (VNC) were found apically, basally, and closer to the ventral midline. We used lineage tracing to characterize the changing boundary of the trunk neuroectoderm. Finally, to start to generate a genetic hierarchy, we performed double-fluorescent in-situ hybridization (FISH) and single-FISH plus EdU labeling for neurogenic gene homologs. In the brain and VNC, Ct-soxB1 and Ct-neurogenin were expressed in a large proportion of apically-localized, EdU+ NPCs. In contrast, Ct-ash1 was expressed in a small subset of apically-localized, EdU+ NPCs and subsurface, EdU- cells, but not in Ct-neuroD+ or Ct-elav1+ cells, which also were subsurface. CONCLUSIONS: Our data suggest a putative genetic hierarchy with Ct-soxB1 and Ct-neurogenin at the top, followed by Ct-ash1, then Ct-neuroD, and finally Ct-elav1. Comparison of our data with that from Platynereis dumerilii revealed expression of neurogenin homologs in proliferating NPCs in annelids, which appears different than the expression of vertebrate neurogenin homologs in cells that are exiting the cell cycle. Furthermore, differences between neurogenesis in the head versus trunk of C. teleta suggest that these two tissues may be independent developmental modules, possibly with differing evolutionary trajectories.

Correction: In situ crosslinking of electrospun gelatin for improved fiber morphology retention and tunable degradation.

Correction for 'In situ crosslinking of electrospun gelatin for improved fiber morphology retention and tunable degradation' by A. P. Kishan et al., J. Mater. Chem. B, 2015, DOI: .

In situ crosslinking of electrospun gelatin for improved fiber morphology retention and tunable degradation.

Electrospinning is a popular technique to fabricate tissue engineering scaffolds due to the exceptional tunability of the fiber morphology, which can be used to control the scaffold mechanical properties, degradation rate, and cell behavior. Recent work has focused on electrospinning natural polymers such as gelatin to improve the regeneration potential of these grafts. Gelatin scaffolds must be crosslinked to avoid rapid dissolution upon implantation with current crosslinking strategies requiring additional post-processing steps. Despite the strong dependence of scaffold properties on fiber morphology, there has been minimal emphasis on retaining the original fiber morphology of electrospun gelatin scaffolds after implantation. This work describes a method for in situ crosslinking of gelatin to produce electrospun fibers with improved fiber morphology retention after implantation. A double barrel syringe with an attached mixing head and a diisocyanate crosslinker were utilized to generate electrospun scaffolds that crosslink during the electrospinning process. These in situ crosslinked fiber meshes retained morphology after 1 week incubation in water at 37 °C; whereas, uncrosslinked meshes lost the fibrous morphology within 24 hours. Degree of crosslinking was quantified and relationships between the crosslinker ratio and enzymatic degradation rate were evaluated. The degradation rate decreased with increased crosslinker ratio, resulting in a highly tunable system. Additionally, tensile testing under simulated physiological conditions indicated that increased crosslinker ratios resulted in increases in initial modulus and tensile strength. Overall, this in situ crosslinking technique provides a method to crosslink gelatin during electrospinning and can be used to tune the degradation rate of resulting scaffolds while enabling improved fiber morphology retention after implantation.

Energy expenditures of mechanically ventilated nonsurgical patients.

Mechanically ventilated, nonsurgical, critically ill patients represent a group not rigorously studied by energy expenditure measurements for formulating nutritional support guidelines. Most strategies for predicting caloric requirements in this group are based on studies of spontaneously breathing surgical patients. It is unclear whether "severity of disease" or "stress" factors employed in this group are justifiable in medical patients with compromised pulmonary function, who may be particularly prone to the complications of overfeeding. We therefore measured the energy expenditures of 73 consecutive ventilator-supported patients with various primary diagnoses in a medical ICU. These results are compared to estimates of caloric requirements based on the Harris-Benedict equations, without modification for severity of disease or other factors. These comparisons are (kcal/day +/- SE, measured vs predicted): sepsis, 1,982 +/- 97 vs 1,534 +/- 56 (p less than 0.0001); cardiogenic shock, 1,452 +/- 119 vs 1,339 +/- 62; cardiogenic pulmonary edema, 1,427 +/- 87 vs 1,338 +/- 93; ARDS, 1,732 +/- 203 vs 1,550 +/- 125; pneumonia, 1,508 +/- 148 vs 1,259 +/- 55; and "other" 1,585 +/- 104 vs 1,419 +/- 55. These data reveal that in mechanically ventilated nonsurgical patients without sepsis, no modifications of the Harris-Benedict equations are necessary; in those with sepsis an increase of approximately 20 percent over these predictions is appropriate.