Biology subjects

Copp, A. J.

Publications and source records attributed to Copp, A. J..

3 recordsLinked to original sources

bioRxiv2023

Spinal neural tube formation and regression in human embryos

Formation of the nervous system in the spinal region of higher vertebrates involves primary and secondary neurulation, in which the neural tube forms by closure and canalisation respectively. These processes are incompletely understood in humans, in part due to the challenge of accessing neurulation-stage embryos (3-7 weeks post-conception). Here we present findings on completion of primary neurulation and formation of the secondary body (including secondary neurulation) in 108 human embryos that span Carnegie Stages (CS) 10 to 18. Several outstanding questions on low spinal development in humans are addressed: we show that primary neurulation is completed at the human posterior neuropore with a pattern of neural plate bending similar to that in the mouse. There is no evidence of a transition zone to secondary neurulation, which proceeds from CS13 with formation of a single lumen as in mouse, not coalescence of multiple lumens as has been claimed based on chick neurulation. Secondary neural tube splitting is seen in the more proximal tail regions of 60% of human embryos. A somite is formed every 7 h in human, compared with 2 h in mice and a 5 h segmentation clock in human organoids. Termination of axial elongation occurs after downregulation of WNT3A and FGF8 in the CS15 embryonic tailbud, with a burst of apoptosis that may remove the neuro-mesodermal progenitors. We conclude that low spinal neurulation and secondary body formation follow a similar pattern in humans as in mammalian model systems such as mouse and rat. Investigators are now attempting to recapitulate events of neurulation in organoids derived from human stem cells, and our findings provide normative data for interpretation of such in vitro results.

developmental biology↗

bioRxiv2023

Caudal Fgfr1 disruption produces localised spinal mis-patterning and a terminal myelocystocele-like phenotype in mice

Closed spinal dysraphisms are poorly understood neurodevelopmental malformations commonly classed as neural tube defects. Several, including terminal myelocystocele, selectively affect the distal lumbosacral spine. We previously identified a neural tube closure-initiating point, Closure 5, involved in forming the distal spine of mice. Here we document equivalent morphology of the caudal-most end of the closing posterior neuropore (PNP) in mice and humans, suggesting Closure 5 is conserved in humans. It forms in a region of active fibroblast growth factor (FGF) signalling and pharmacological blockade of FGF receptors (Fgfr) impairs Closure 5 formation in cultured mouse embryos. Conditional genetic deletion of Fgfr1 in caudal embryonic tissues with Cdx2Cre similarly impairs Closure 5 formation and leads to morphologically abnormal PNPs, which nonetheless achieve delayed closure although delayed. After PNP closure, a localised region of the distal neural tube of Fgfr1-disrupted embryos re-opens into a trumpet-like flared central canal between the presumptive hindlimbs, progressing to form a distal fluid-filled sac overlying ventrally flattened spinal cord. This phenotype resembles terminal myelocystocele. Histological analysis of spinal progenitor domains reveals regional and progressive loss of ventral spinal cord progenitor domains preceding cystic dilation of the central canal. Initially, the Shh and FoxA2-positive ventral domains are lost, resulting in Olig2-labelling of the ventral-most neural tube. The Olig2-domain is also subsequently lost, eventually producing a neural tube entirely positive for the dorsal marker Pax3. Thus, a terminal myelocystocele-like phenotype can arise after completion of neural tube closure due to localised spinal mis-patterning caused by disruption of Fgfr1 signalling.

developmental biology↗

bioRxiv2021

Severe neural tube defects due to failure of closure initiation can arise without abnormality of neuroepithelial convergent extension

Planar cell polarity (PCP) signalling is vital for initiation of neural tube closure in mice, with diminished convergent extension (CE) cell movements leading to a severe form of neural tube defect (NTD), termed craniorachischisis (CRN). Some human NTDs are also associated with PCP gene mutations, but affected individuals are generally heterozygous, whereas PCP homozygosity or compound heterozygosity is needed to produce CRN in mice. This suggests human NTDs may involve other genetic or environmental factors, that interact with partial loss of PCP function. We found that reduced sulfation OF glycosaminoglycans (GAGs) interacts with heterozygosity for the Lp allele of Vangl2 (a core PCP gene), to cause CRN in mice. Here, we hypothesised that this GAG-PCP interaction may regulate convergent extension movements, and hence lead to severe NTDs in the context of only partial loss of PCP function. Both Lp and null alleles of Vangl2 gave similar findings. Culture of E8.5 embryos in the presence of chlorate (a GAG sulfation inhibitor), or enzymatic cleavage of GAG chains, led to failure of NT closure initiation in the majority of Lp/+ embryos, whereas few +/+ littermates exhibited CRN. The chlorate effect was rescued by exogenous sulphate. Surprisingly, DiO labeling of the embryonic node demonstrated no abnormality of midline axial extension in chlorate-treated Lp/+ embryos that developed CRN. In contrast, positive control Lp/Lp embryos displayed severe convergent extension defects in this assay. Morphometric analysis of the closure initiation site revealed abnormalities in the size and shape of somites that flank the closing neural tube in chlorate-treated Lp/+ embryos. We conclude that severe NTDs involving failure of closure initiation can arise by a mechanism other than faulty neuroepithelial convergent extension. Matrix-mediated expansion of somites, flanking the closing neural tube, may be required for closure initiation.

developmental biology↗