1
|
Tait CM, Chinnaiya K, Manning E, Murtaza M, Ashton JP, Furley N, Hill CJ, Alves CH, Wijnholds J, Erdmann KS, Furley A, Rashbass P, Das RM, Storey KG, Placzek M. Crumbs2 mediates ventricular layer remodelling to form the spinal cord central canal. PLoS Biol 2020; 18:e3000470. [PMID: 32150534 PMCID: PMC7108746 DOI: 10.1371/journal.pbio.3000470] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2019] [Revised: 03/31/2020] [Accepted: 02/18/2020] [Indexed: 11/27/2022] Open
Abstract
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 Crb2F/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.
Collapse
Affiliation(s)
- Christine M Tait
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - Kavitha Chinnaiya
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - Elizabeth Manning
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - Mariyam Murtaza
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - John-Paul Ashton
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - Nicholas Furley
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - Chris J Hill
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - C Henrique Alves
- Department of Ophthalmology, Leiden University Medical Centre, Leiden, the Netherlands
| | - Jan Wijnholds
- Department of Ophthalmology, Leiden University Medical Centre, Leiden, the Netherlands
| | - Kai S Erdmann
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - Andrew Furley
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - Penny Rashbass
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| | - Raman M Das
- Division of Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Kate G Storey
- Division of Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Marysia Placzek
- Department of Biomedical Science and Bateson Centre, University of Sheffield, Sheffield, United Kingdom
| |
Collapse
|
2
|
Sepich DS, Solnica-Krezel L. Intracellular Golgi Complex organization reveals tissue specific polarity during zebrafish embryogenesis. Dev Dyn 2016; 245:678-91. [PMID: 27043944 DOI: 10.1002/dvdy.24409] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Revised: 03/15/2016] [Accepted: 03/29/2016] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Cell polarity is essential for directed migration of mesenchymal cells and morphogenesis of epithelial tissues. Studies in cultured cells indicate that a condensed Golgi Complex (GC) is essential for directed protein trafficking to establish cell polarity underlying directed cell migration. Dynamic changes of the GC intracellular organization during early vertebrate development remain to be investigated. RESULTS We used antibody labeling and fusion proteins in vivo to study the organization and intracellular placement of the GC during early zebrafish embryogenesis. We found that the GC was dispersed into several puncta containing cis- and trans-Golgi Complex proteins, presumably ministacks, until the end of the gastrula period. By early segmentation stages, the GC condensed in cells of the notochord, adaxial mesoderm, and neural plate, and its intracellular position became markedly polarized away from borders between these tissues. CONCLUSIONS We find that GC is dispersed in early zebrafish cells, even when cells are engaged in massive gastrulation movements. The GC accumulates into patches in a stage and cell-type specific manner, and becomes polarized away from borders between the embryonic tissues. With respect to tissue borders, intracellular GC polarity in notochord is independent of mature apical/basal polarity, Wnt/PCP, or signals from adaxial mesoderm. Developmental Dynamics 245:678-691, 2016. © 2016 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- Diane S Sepich
- Department of Developmental Biology, Washington University School of Medicine, St Louis, Missouri
| | - Lila Solnica-Krezel
- Department of Developmental Biology, Washington University School of Medicine, St Louis, Missouri
| |
Collapse
|
3
|
Kondrychyn I, Teh C, Sin M, Korzh V. Stretching morphogenesis of the roof plate and formation of the central canal. PLoS One 2013; 8:e56219. [PMID: 23409159 PMCID: PMC3567028 DOI: 10.1371/journal.pone.0056219] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Accepted: 01/07/2013] [Indexed: 12/20/2022] Open
Abstract
Background Neurulation is driven by apical constriction of actomyosin cytoskeleton resulting in conversion of the primitive lumen into the central canal in a mechanism driven by F-actin constriction, cell overcrowding and buildup of axonal tracts. The roof plate of the neural tube acts as the dorsal morphogenetic center and boundary preventing midline crossing by neural cells and axons. Methodology/Principal Findings The roof plate zebrafish transgenics expressing cytosolic GFP were used to study and describe development of this structure in vivo for a first time ever. The conversion of the primitive lumen into the central canal causes significant morphogenetic changes of neuroepithelial cells in the dorsal neural tube. We demonstrated that the roof plate cells stretch along the D–V axis in parallel with conversion of the primitive lumen into central canal and its ventral displacement. Importantly, the stretching of the roof plate is well-coordinated along the whole spinal cord and the roof plate cells extend 3× in length to cover 2/3 of the neural tube diameter. This process involves the visco-elastic extension of the roof place cytoskeleton and depends on activity of Zic6 and the Rho-associated kinase (Rock). In contrast, stretching of the floor plate is much less extensive. Conclusions/Significance The extension of the roof plate requires its attachment to the apical complex of proteins at the surface of the central canal, which depends on activity of Zic6 and Rock. The D–V extension of the roof plate may change a range and distribution of morphogens it produces. The resistance of the roof plate cytoskeleton attenuates ventral displacement of the central canal in illustration of the novel mechanical role of the roof plate during development of the body axis.
Collapse
Affiliation(s)
- Igor Kondrychyn
- Institute of Molecular and Cell Biology, A-STAR, Singapore, Singapore
| | - Cathleen Teh
- Institute of Molecular and Cell Biology, A-STAR, Singapore, Singapore
| | - Melvin Sin
- Institute of Molecular and Cell Biology, A-STAR, Singapore, Singapore
| | - Vladimir Korzh
- Institute of Molecular and Cell Biology, A-STAR, Singapore, Singapore
- Department of Biological Sciences, National University of Singapore, Singapore, Singapore
- * E-mail:
| |
Collapse
|
4
|
van der Put NM, van Straaten HW, Trijbels FJ, Blom HJ. Folate, homocysteine and neural tube defects: an overview. Exp Biol Med (Maywood) 2001; 226:243-70. [PMID: 11368417 DOI: 10.1177/153537020122600402] [Citation(s) in RCA: 211] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Folate administration substantially reduces the risk on neural tube detects (NTD). The interest for studying a disturbed homocysteine (Hcy) metabolism in relation to NTD was raised by the observation of elevated blood Hcy levels in mothers of a NTD child. This observation resulted in the examination of enzymes involved in the folate-dependent Hcy metabolism. Thus far, this has led to the identification of the first and likely a second genetic risk factor for NTD. The C677T and A1298C mutations in the methylenetetrahydrofolate reductase (MTHFR) gene are associated with an increased risk of NTD and cause elevated Hcy concentrations. These levels can be normalized by additional folate intake. Thus, a dysfunctional MTHFR partly explains the observed elevated Hcy levels in women with NTD pregnancies and also, in part, the protective effect of folate on NTD. Although the MTHFR polymorphisms are only moderate risk factors, population-wide they may account for an important part of the observed NTD prevalence.
Collapse
Affiliation(s)
- N M van der Put
- Department of Pediatrics, University Medical Center Nijmegen, The Netherlands.
| | | | | | | |
Collapse
|
5
|
van Straaten HW, Peeters MC, Szpak KF, Hekking JW. Initial closure of the mesencephalic neural groove in the chick embryo involves a releasing zipping-up mechanism. Dev Dyn 1997; 209:333-41. [PMID: 9264257 DOI: 10.1002/(sici)1097-0177(199708)209:4<333::aid-aja1>3.0.co;2-j] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
According to a traditional viewpoint, initial closure of the anterior neural groove involves bilateral elevation of the edges of the neural plate, flattening of the midline area, subsequent convergence of the dorsal neural folds, and finally adhesion and fusion of the medial fold edges. In a transverse view, the shape of the neural groove thereby changes from V > U > toppled C > O. This sequence implicates that the neural groove is wide almost from its inception. In the present study, a new mechanism of initial closure is proposed, based on observations in living chick embryos and on light and scanning electron microscopic observations during neurulation in the presumptive mesencephalic region. The medial part of the neural plate invaginates in ventral direction. The walls of the arising neural groove appose, beginning in the depth, and make subsequent contact. During continued invagination the neural walls extend in ventral direction, the apposition/contact zone shifts in dorsal direction up to the neural folds and the neural walls separate ventrally, resulting in the incipient neural tube lumen. The mechanism is best compared with a zipping-up releasing model. In a transverse view, the shape of the neural groove changes from V > Y > I > O. While, according to the traditional view, the neural folds have to converge from a distance in order to contact each other, in the present mechanism the walls and folds are sequentially in contact by the ventro-dorsal zipping-up mechanism, thereby avoiding the possibility of mismatch of the neural folds. The above process is initiated over a considerable longitudinal distance along the neural plate, but only at the mesencephalic level does the dorsal shift of the contact zone become complete. At other levels of the neuraxis, the contact zone releases prematurely and the neural walls become widely separated well before their dorsal neural folds are in contact. These folds have to converge, therefore, in order to close, but their matching is facilitated by the alignment of the previously contacted neural folds at the mesencephalic level as well as by guidance underneath the vitelline membrane.
Collapse
Affiliation(s)
- H W van Straaten
- Department of Anatomy/Embryology, University of Maastricht, The Netherlands.
| | | | | | | |
Collapse
|
6
|
Wilson DB, Wyatt DP. Aberrant convergence of the neural folds in the mouse mutant vl. TERATOLOGY 1992; 45:105-12. [PMID: 1731393 DOI: 10.1002/tera.1420450110] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Progressive changes in the dorsolateral angles (DA) and ventral angle (VA) during elevation and convergence of the caudal neural folds were morphometrically analyzed in normal and dysraphic abnormal embryos of the mouse mutant vacuolated lens (vl), and correlations with the configuration of microfilaments in the apices of neuroepithelial cells were made by means of ultrastructural cytochemistry. In 22-28 somite stage abnormal (vl/vl) embryos, the DA and VA are larger than those in their normal counterparts at each comparable level of the caudal neural folds, suggesting that defective convergence involves both the DA and VA in this mutant. In 30-35 somite stage abnormal embryos, the VA is likewise larger than that in normal embryos in which the neural folds have converged and closed; however, the DAs are much smaller, indicating that a medial collapse of the dorsal ends of the neural folds may occur secondary to the closure failure. At the DA, the ultrastructural configuration of microfilaments is similar in abnormal and normal embryos in terms of their circumferential arrangement around the perimeters of the neuroepithelial cell apices. In abnormal embryos, however, the bundles of microfilaments are more delicate and less prominent than in normal embryos; thus it is possible that a quantitative and/or functional deficiency in these elements may be involved in the failure of the abnormal neuroepithelium to bend properly during convergence of the neural folds.
Collapse
Affiliation(s)
- D B Wilson
- Division of Anatomy, University of California, San Diego, School of Medicine, La Jolla 92093
| | | |
Collapse
|
7
|
Jaskoll T, Greenberg G, Melnick M. Neural tube and neural crest: a new view with time-lapse high-definition photomicroscopy. AMERICAN JOURNAL OF MEDICAL GENETICS 1991; 41:333-45. [PMID: 1789290 DOI: 10.1002/ajmg.1320410315] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The dynamic process of neural tube formation and neural crest migration in live, unstained cultured avian embryos at Hamburger-Hamilton (H.H.) stages 8-11 was investigated by time-lapse cinematography using a high-definition microscope. These studies have demonstrated that neural tube closure in the trunk region differs from that observed in the head. The cephalic neural folds elevate slowly, then make contact rapidly. Following this initial apposition, they gradually "zip-up" in the rostrad and caudad direction. In the trunk region where the neuroepithelium bulges adjacent to the somites, the edges of the folds pulsate and forcefully touch-retract-touch in these bulging regions; the intersomitic epithelia retract, remain open even after more posterior somitic regions have apposed, and then close slowly. Epithelial blebs and N-CAM antibody were observed at the leading edges of the neuroepithelia. Between the open folds only a few bridging cells were seen; they probably represent the sites of initial cell adhesion following epithelial retraction. Focusing into the developing embryo shows that neuroepithelial fusion occurs prior to surface epithelial fusion. A meshwork of synchronously pulsating neural crest cells was identified below the surface epithelium and a preliminary investigation of their initial migration was conducted.
Collapse
Affiliation(s)
- T Jaskoll
- Department of Basic Science, University of Southern California Dental School, Los Angeles 90089-0641
| | | | | |
Collapse
|
8
|
Nagele RG, Bush KT, Lynch FJ, Lee HY. A morphometric and computer-assisted three-dimensional reconstruction study of neural tube formation in chick embryos. Anat Rec (Hoboken) 1991; 231:425-36. [PMID: 1793173 DOI: 10.1002/ar.1092310405] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The origin of the driving forces for neural tube formation remains uncertain but is currently thought to involve the participation of microfilament bundles situated in the apical ends of neuroepithelial cells. In the work presented here, we show how morphometric measurements that map local variations in the apical geometry of neuroepithelial cells (especially apical constriction) can provide information on the distribution of motive forces within the neuroepithelium during neural tube formation. When used in combination with computer-assisted, three-dimensional reconstruction, it becomes possible to analyze the morphometric data from a dynamic, three-dimensional perspective. As an example application of this method, we have used morphometry to evaluate the effects of ionomycin on the developing neuroepithelium. Treatment of early (stages 6-8) chick embryos with 5 microM ionomycin was found to cause rapid bending of the neuroepithelium within 1 min of exposure and a dramatic acceleration of the normal sequence of neural tube formation. Electron microscopy and morphometry revealed that this acceleration was coincident with a marked increase in the local degree of apical constriction of neuroepithelial cells, presumably a consequence of enhanced contractile activity of apical microfilament bundles. This work shows that transient elevation of free calcium levels can accelerate the usual sequential phases of NT formation. The rapidity of the response (hours of normal development reduced to minutes), increased prominence of apical microfilament bundles, and the enhanced degree of apical constriction strongly support a direct causal role for apical microfilament bundles and apical constriction of neuroepithelial cells in bending of the neuroepithelium.
Collapse
Affiliation(s)
- R G Nagele
- Department of Cell Biology, School of Osteopathic Medicine, University of Medicine and Dentistry of New Jersey 08103
| | | | | | | |
Collapse
|
9
|
van Straaten HW, Hekking JW. Development of floor plate, neurons and axonal outgrowth pattern in the early spinal cord of the notochord-deficient chick embryo. ANATOMY AND EMBRYOLOGY 1991; 184:55-63. [PMID: 1928744 DOI: 10.1007/bf01744261] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The notochord is probably involved in the development of the neural tube. In this study, a fragment of caudal notochord was extirpated in ovo from chick embryos at 1.5 days of incubation. At 4.5 days a distinct notochord-deficient region at thoracolumbar level was found. Profound effects were seen, especially at the cranial site of this region. Somites were smaller than normal, or even not recognizable, and in some cases the myotomes were fused in the midline. The spinal cord appeared reduced in size and lacked a floor plate. The average amount of spinal cord neurons was 23% of the normal value, the cells being located circularly along the outer margin of the spinal cord, except for the roof plate. Axonal roots left the cord in the ventral midline only. Caudal to this site, neurons or floor plate cells were alternately present in the ventral spinal cord, and axonal roots left bilaterally. In a caudal direction, a normal morphology gradually reappeared. The possibility is discussed that reduction in spinal cord size and amount of neurons is a direct or indirect effect of the absence of the notochord, and that the sclerotome may be involved.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- H W van Straaten
- Department of Anatomy and Embryology, School of Medicine, University of Limburg, Maastricht, The Netherlands
| | | |
Collapse
|
10
|
Coelho CN, Klein NW. Methionine and neural tube closure in cultured rat embryos: morphological and biochemical analyses. TERATOLOGY 1990; 42:437-51. [PMID: 2256006 DOI: 10.1002/tera.1420420412] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
When headfold-stage rat embryos were cultured on cow serum, their neural tubes failed to close unless the serum was supplemented with methionine. Methionine deficiency did not appear to affect the ability of the neural epithelium to fuse as a type of fusion was observed between anterior and posterior regions of the open neural tube in methionine-deficient embryos. Although methionine deficiency reduced the cell density and mitotic indices of cranial mesenchyme and neural epithelial cells, this did not appear to be a factor in failure of the neural tube to close. For example, embryos cultured on diluted cow serum also had fewer mesenchymal cells yet could complete neural tube closure if provided with methionine. Examination of the tips of the neural folds suggested that microfilament contraction could be involved; in the absence of methionine the neural folds failed to turn in. This possibility was supported by the reductions in neurite extension of isolated neural tubes cultured without methionine and by the reductions in microfilament associated methylated amino acids contained in embryo neural tube proteins.
Collapse
Affiliation(s)
- C N Coelho
- Center for Environmental Health, University of Connecticut, Storrs 06269
| | | |
Collapse
|
11
|
Bush KT, Lynch FJ, DeNittis AS, Steinberg AB, Lee HY, Nagele RG. Neural tube formation in the mouse: a morphometric and computerized three-dimensional reconstruction study of the relationship between apical constriction of neuroepithelial cells and the shape of the neuroepithelium. ANATOMY AND EMBRYOLOGY 1990; 181:49-58. [PMID: 2305970 DOI: 10.1007/bf00189727] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Morphometry and computerized three-dimensional reconstruction were used to study the relationship between apical constriction of neuroepithelial cells and the pattern of bending of the neuroepithelium in the developing neural tube of the 12-somite mouse embryo. The neuroepithelium of the mouse exhibits prominent regional variations in size and shape along the embryo axis. The complex shape of most of the cephalic neural tube (e.g., forebrain and midbrain) is due to the coexistence of concave and convex bending sites whereas more caudal regions (e.g., hindbrain and spinal cord) generally lack sites of convex bending and have a relatively simple shape. The apical morphology of neuroepithelial cells was found to be correlated more closely with the local status of bending of the neuroepithelium than with the specific region of the neural tube in which they are located. In areas of enhanced apical constriction, microfilament bundles were particularly prominent. Morphometry revealed that patterns of bending of the neuroepithelium were correlated almost exactly with those of apical constriction throughout the forming neural tube. These findings support the idea that apical constriction of neuroepithelial cells, resulting from tension generated by microfilament bundles, plays a major role in bending of the neuroepithelium during neural tube formation in the mouse.
Collapse
Affiliation(s)
- K T Bush
- Department of Biology, Rutgers University, Camden, NJ 08102
| | | | | | | | | | | |
Collapse
|
12
|
Nagele RG, Bush KT, Kosciuk MC, Hunter ET, Steinberg AB, Lee HY. Intrinsic and extrinsic factors collaborate to generate driving forces for neural tube formation in the chick: a study using morphometry and computerized three-dimensional reconstruction. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1989; 50:101-11. [PMID: 2582601 DOI: 10.1016/0165-3806(89)90129-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The formation of the neural tube, the rudiment of the entire central nervous system, is one of the earliest morphogenetic movements. The origin of the driving forces for this process remains uncertain, but recent studies suggest the involvement of both intrinsic and extrinsic factors. In the present study, we have used morphometry, analysis of stereopair photographs of whole embryos, and computerized three-dimensional reconstruction to investigate the factors which constitute the bulk of the driving forces for neural tube formation in the developing midbrain of Hamburger and Hamilton stages 5-9 chick embryos. Results support the notion that neural tube formation is driven by a coordinated interplay of intrinsic and extrinsic forces. Initial bending of the neural plate along the midline of the embryo and uplifting of the neural folds is accomplished primarily through the combined action of intrinsic forces (resulting from apical constriction of neuroepithelial cells) and extrinsic forces (mostly a passive consequence of head-fold formation). However, once in the uplifted position, curling over of neural folds and closure of the neural tube is driven largely by apical constriction-mediated (intrinsic) forces that are generated by cells in the midlateral walls of the forming neural tube.
Collapse
Affiliation(s)
- R G Nagele
- Department of Pediatrics, University of Medicine and Dentistry of New Jersey-School of Osteopathic Medicine, Camden 08103
| | | | | | | | | | | |
Collapse
|
13
|
Nagele RG, Bush KT, Hunter ET, Kosciuk MC, Lee H. Biomechanical basis of diazepam-induced neural tube defects in early chick embryos: a morphometric study. TERATOLOGY 1989; 40:29-36. [PMID: 2763208 DOI: 10.1002/tera.1420400105] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The biomechanical basis of diazepam (Valium/Roche)-induced neural tube defects in the chick was investigated using a combination of electron microscopy and morphometry. Embryos at stage 8 (four-somite stage) of development were explanted and grown for 6 hr in nutrient medium containing 400 micrograms/ml diazepam. Nearly 80% of these embryos exhibited neural tube defects that were most pronounced in the forming midbrain region and typified by a "relaxation" or "collapse" of neural folds. The hindbrain and spinal cord regions were less affected. Electron microscopy revealed that neuroepithelial cells in diazepam-treated embryos had smoother apical surfaces and broader apical widths than did controls. Morphometric measurements supported this observation and further showed that these effects were focused at sites within the wall of the forming neural tube that typically exhibit the greatest degree of bending and apical constriction (i.e., the floor and midlateral walls). Overall results indicate that neural tube defects associated with exposure to diazepam are due largely to a general inhibition of the contractile activity of apical microfilament bundles in neuroepithelial cells. These findings 1) emphasize the important contribution of microfilament-mediated apical constriction of neuroepithelial cells in providing the driving forces for bending of the neuroepithelium during neural tube formation and 2) suggest that agents or conditions that impair their contractile activity could play a role in the pathogenesis of certain types of neural tube defects.
Collapse
Affiliation(s)
- R G Nagele
- Department of Pediatrics, University of Medicine and Dentistry of New Jersey, School of Osteopathic Medicine, Camden 08103
| | | | | | | | | |
Collapse
|