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.

Conservative approach to the management of morbidly adherent placentae.

OBJECTIVE: To determine the effect of conservative management of morbidly adherent placentae on maternal morbidity and mortality and to review management options METHODS: All case notes of patients with placenta accreta and percreta between June 2008 and August 2010 were studied retrospectively. RESULTS: Eight placentae percretae and 4 placentae accretae were identified out of a total of 11,358 deliveries.All 12 patients underwent caesarean section. Placentae percretae were intentionally left in situ. Interventional radiology was used in these cases. There was one emergency hysterectomy for massive obstetric haemorrhage,one case of disseminated intravascular coagulation,one case of early sepsis and 3 cases of delayed sepsis.Average blood loss was 2490 ml with the mean volume transfused being 1425 ml. The mean hospital stay was 7 days and 2 patients were admitted to intensive care. One patient was readmitted with sepsis complicated by a utero-cutaneous fistula (complete placenta praevia).Another patient required re-embolisation 5 months post delivery for persistent haemorrhage. No ureteric or bladder injuries occurred. CONCLUSIONS: Conservative management of placenta percreta is an alternative to caesarean hysterectomy. It is associated with lower maternal morbidity rates.However, monitoring for sepsis and secondary postpartum haemorrhage is essential. Rare complications such as utero-cutanus fistulae may occur.