In the spinal cord, the central canal forms through a poorly understood process termed dorsal collapse that involves attrition and remodelling of pseudostratified ventricular layer (VL) cells. Here, we use mouse and chick models to show that dorsal ventricular layer (dVL) cells adjacent to dorsal midline Nestin (+) radial glia (dmNes + RG) down-regulate apical polarity proteins, including Crumbs2 (CRB2) and delaminate in a stepwise manner; live imaging shows that as one cell delaminates, the next cell ratchets up, the dmNes + RG endfoot ratchets down, and the process repeats. We show that dmNes + RG secrete a factor that promotes loss of cell polarity and delamination. This activity is mimicked by a secreted variant of Crumbs2 (CRB2S) which is specifically expressed by dmNes + RG. In cultured MDCK cells, CRB2S associates with apical membranes and decreases cell cohesion. Analysis of Crb2 F/F /Nestin-Cre +/− mice, and targeted reduction of Crb2/CRB2S in slice cultures reveal essential roles for transmembrane CRB2 (CRB2TM) and CRB2S on VL cells and dmNes + RG, respectively. We propose a model in which a CRB2S-CRB2TM interaction promotes the progressive attrition of the dVL without loss of overall VL integrity. This novel mechanism may operate more widely to promote orderly progenitor delamination. PLOS BIOLOGYPLOS Biology | https://doi.org/10.box transcription factors, SOXB1 [1], a feature of their neuroepithelial origin [2,3], and differentially express homeodomain transcription factors, a feature of dorsoventral patterning [4][5][6]. In early embryogenesis, VL cells undergo neurogenesis in a process that involves apical constriction, adherens-junction disassembly, acto-myosin-mediated abscission and mediolateral migration [7,8]. Following the major period of neurogenesis, VL cells switch to gliogenesis, and glial cells migrate out of this layer [9][10][11][12].Concomitant with the transition to gliogenesis (around E12 in the mouse) the VL begins to remodel, ultimately giving rise to the ependymal layer (EL) surrounding the adult central canal. Ependymal cells constitute key components of a quiescent stem cell niche [13][14][15], are implicated in glial scar formation after spinal injury [15][16][17], and serve important mechanical and sensory functions [18,19]. Multiple steps contribute to the remodelling of the VL into the EL [1,20], including dorsal collapse, a delamination of dorsal ventricular layer cells (hereafter termed dVL cells) that results in a pronounced dorsoventral reduction in the length of the lumen [20][21][22][23][24][25][26][27][28]. Little is understood, however, of the mechanisms that mediate dorsal collapse.Proteins of the Crumbs (CRB) and PAR complexes (the latter composed of PAR3/PAR6/ aPKC) are present on the apical side of epithelial cells. In invertebrates, PAR-and CRB-complex proteins directly interact to determine the apicobasal axis and the position and stability of cell-cell adherens junctions [29][30][31][32][33][34][35][36]. PAR and CRB complex components are evolutionarily conse...

Understanding the loss of conserved genes is critical for determining how phenotypic diversity is generated. Here we focus on the evolution of DCC, a gene that encodes a highly conserved neural guidance receptor. Disruption of DCC in animal models and humans results in major neurodevelopmental defects including commissural axon defects. Here we examine DCC evolution in birds, which is of particular interest as a major model system in neurodevelopmental research. We found the DCC containing locus was disrupted several times during evolution, resulting in both gene losses and faster evolution rate of salvaged genes. These data suggest that DCC had been lost independently twice during bird evolution, including in chicken and zebra finch, whereas it was preserved in many other closely related bird species, including ducks. Strikingly, we observed that commissural axon trajectory appeared similar regardless of whether DCC could be detected or not. We conclude that the DCC locus is susceptible to genomic instability leading to independent disruptions in different branches of birds and a significant influence on evolution rate. Overall, the phenomenon of loss or molecular evolution of a highly conserved gene without apparent phenotype change is of conceptual importance for understanding molecular evolution of key biological processes.

Sensory information relayed to the brain is dependent on complex, yet precise spatial organization of neurons. This anatomical complexity is generated during development from a surprisingly small number of neural stem cell domains. This raises the question of how neurons derived from a common precursor domain respond uniquely to their environment to elaborate correct spatial organization and connectivity. We addressed this question by exploiting genetically labeled mouse embryonic dorsal interneuron 1 (dI1) neurons that are derived from a common precursor domain and give rise to spinal projection neurons with distinct organization of cell bodies with axons projecting either commissurally (dI1c) or ipsilaterally (dI1i). In this study, we examined how the guidance receptor, Robo2, which is a canonical Robo receptor, influenced dI1 guidance during embryonic development. Robo2 was enriched in embryonic dI1i neurons, and loss of Robo2 resulted in misguidance of dI1i axons, whereas dI1c axons remained unperturbed within the mantle zone and ventral commissure. Further, Robo2 profoundly influenced dI1 cell body migration, a feature that was partly dependent on Slit2 signaling. These data suggest that dI1 neurons are dependent on Robo2 for their organization. This work integrated with the field support of a model whereby canonical Robo2 vs. non-canonical Robo3 receptor expression facilitates projection neurons derived from a common precursor domain to read out the tissue environment uniquely giving rise to correct anatomical organization.

A chronic wound audit was carried out at the Conquest Hospital, East Sussex, to establish the prevalence of chronic wounds within the Trust, in light of evaluation of the tissue viability service. At the time of audit the Trust employed two specialist nurses on a part time basis (3 days a week) with 2 days clinical work on the wards. A total of 372 patients were included in the audit, 56 patients had a total of 82 chronic wounds. These wounds were subdivided into wound types. The highest numbers of chronic wounds were pressure ulcers grade 1-4, including the new category of moisture lesions totalling 47.5%. Surgical wounds followed at 20.7%. There was a marked reduction in grade 3-4 pressure ulcers consistent with the pressure ulcer prevalence report from August 2006 that saw an overall reduction of hospital acquired pressure ulcers of 3.9%. This was attributed to the purchase of pressure relieving equipment, the development of a pressure ulcer help line and focused education on pressure ulcer prevention throughout the wards. The mean bed stay for both medical and surgical patients was 28.5 bed days but with surgical patients alone median bed stay was a staggering 45.5 days.

In the spinal cord, the adult central canal forms through a poorly-understood process termed dorsal collapse that involves attrition and remodelling of the pseudostratified dorsal ventricular layer. Here we show, in mouse, that dorsal ventricular layer cells adjacent to midline Nestin (+) radial glia downregulate the apical polarity proteins Crumbs2 (CRB2) and aPKC and delaminate in a step-wise manner; concomitantly, Nestin (+) radial glial end-feet ratchet down, to repeat this process. Nestin (+) radial glia secrete a factor that promotes cell delamination. This activity is mimicked by a secreted variant of CRB2 (CRB2S), which is specifically expressed by dorsal midline Nestin (+) radial glia. In cultured cells, CRB2S associated with apical membranes and decreased cell cohesion. Analysis of Crb2 F/F /Nestin-Cre +/− mice further confirmed an essential role for CRB2 in dorsal collapse. We propose a model in which CRB2S promotes the progressive attrition of the ventricular layer without loss of overall integrity. This novel mechanism may operate more widely to promote orderly progenitor delamination.