Dataset Information

Actomyosin stiffens the vertebrate embryo during crucial stages of elongation and neural tube closure.

ABSTRACT: Physical forces drive the movement of tissues within the early embryo. Classical and modern approaches have been used to infer and, in rare cases, measure mechanical properties and the location and magnitude of forces within embryos. Elongation of the dorsal axis is a crucial event in early vertebrate development, yet the mechanics of dorsal tissues in driving embryonic elongation that later support neural tube closure and formation of the central nervous system is not known. Among vertebrates, amphibian embryos allow complex physical manipulation of embryonic tissues that are required to measure the mechanical properties of tissues. In this paper, we measure the stiffness of dorsal isolate explants of frog (Xenopus laevis) from gastrulation to neurulation and find dorsal tissues stiffen from less than 20 Pascal (Pa) to over 80 Pa. By iteratively removing tissues from these explants, we find paraxial somitic mesoderm is nearly twice as stiff as either the notochord or neural plate, and at least 10-fold stiffer than the endoderm. Stiffness measurements from explants with reduced fibronectin fibril assembly or disrupted actomyosin contractility suggest that it is the state of the actomyosin cell cortex rather than accumulating fibronectin that controls tissue stiffness in early amphibian embryos.

SUBMITTER: Zhou J

PROVIDER: S-EPMC2685957 | biostudies-literature | 2009 Feb

REPOSITORIES: biostudies-literature

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Actomyosin stiffens the vertebrate embryo during crucial stages of elongation and neural tube closure.

Zhou Jian J Kim Hye Young HY Davidson Lance A LA

Development (Cambridge, England) 20090201 4

Physical forces drive the movement of tissues within the early embryo. Classical and modern approaches have been used to infer and, in rare cases, measure mechanical properties and the location and magnitude of forces within embryos. Elongation of the dorsal axis is a crucial event in early vertebrate development, yet the mechanics of dorsal tissues in driving embryonic elongation that later support neural tube closure and formation of the central nervous system is not known. Among vertebrates, ...[more]

PMID: 19168681

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Project description:This data series was used for two separate studies. The initial study was aimed to idenify expression changes brought about by the Cecr2Gt45Bic mutation during neural closure. The study included two different strains, BALB/cCrl in which Cecr2GT45Bic shows a neural tube defect phenotype and FVB/N in which Cecr2Gt45Bic does not manifest neural closure defects. The second was to idenify strain specific expression differences present during neural closure of the mouse embryo between BALB/cCrl and FVB/N in order to identify candidate modifiers of the Cecr2Gt45Bic neural tube defect. Relevant abstracts are included below. The initial study ; BACKGROUND: Over 200 mouse genes are associated with neural tube defects (NTDs), including Cecr2, the bromodomain-containing subunit of the CERF chromatin remodeling complex. METHODS: Gene-trap mutation Cecr2Gt45Bic results in 74% exencephaly (equivalent of human anencephaly) on the BALB/c strain. Gene expression altered during cranial neural tube closure by the Cecr2 mutation was identified through microarray analysis of 11M-bM-^@M-^S14 somites stage Cecr2Gt45Bicembryos. RESULTS: Analysis of Affymetrix Mouse 430 2.0 chips detected 60 transcripts up-regulated and 54 transcripts down-regulated in the Cecr2Gt45Bic embryos (fold > 1.5, p < 0.05). The Cecr2 transcript was reduced only M-bM-^HM-<7- to 14-fold from normal levels, suggesting the Cecr2Gt45Bic is a hypomorphic mutation. We therefore generated a novel Cecr2 null allele (Cecr2tm1.1Hemc). Resulting mutants displayed a stronger penetrance of exencephaly than Cecr2Gt45Bic in both BALB/c and FVB/N strains, in addition to midline facial clefts and forebrain encephalocele in the FVB/N strain. The Cecr2 transcript is reduced 260-fold in the Cecr2tm1.1Hemc line. Subsequent qRT-PCR using Cecr2tm1.1Hemc mutant heads confirmed downregulation of transcription factors Alx1/Cart1,Dlx5, Eya1, and Six1. CONCLUSIONS: As both Alx1/Cart1 and Dlx5 mouse mutations result in exencephaly, we hypothesize that changes in expression of these mesenchymal/ectodermal transcription factors may contribute to NTDs associated with Cecr2. Birth Defects Research (Part A), 2010. 010 Wiley-Liss, Inc. The second study: ABSTRACT:Although neural tube defects (NTDs) are common in humans, little is known about their multifactorial genetic causes. While most mouse models involve NTDs caused by a single mutated gene, we have previously described a multigenic system involving susceptibility to NTDs. In mice with a mutation in Cecr2, the cranial NTD exencephaly shows strain specific differences in penetrance, with 74% penetrance in BALB/cCrl and 0% penetrance in FVB/N. Whole genome linkage analysis showed that a region of chromosome 19 was partially responsible for this difference in penetrance. We now reveal by genetic analysis of three subinterval congenic lines that the chromosome 19 region contains more than one modifier gene. Analysis of embryos showed that although a Cecr2 mutation causes wider neural tubes in both strains, FVB/N embryos overcome this abnormality and close. A microarray analysis comparing neurulating female embryos from both strains identified differentially expressed genes within the chromosome 19 region, including Arhgap19, which is expressed at a lower level in BALB/cCrl due to a stop codon specific to that substrain. Modifier genes in this region are of particular interest because it is syntenic to human chromosome 10q25, the site of a human susceptibility locus. (MANUSCRIPT PENDING SUBMISSION) Thieler STAGE 13-14 (11-14 somite) female embryos where disected away from extraembryonic membranes for RNA extraction and hybridization on Affymetrix microarrays. A single embryo was processed per array, with four biological replicates per genotype BALB/cCrl, Cecr2GT45Bic BALB/cCrl, FVB/N, and Cecr2Gt45Bic FVB/N.

Project description:This data series was used for two separate studies. The initial study was aimed to idenify expression changes brought about by the Cecr2Gt45Bic mutation during neural closure. The study included two different strains, BALB/cCrl in which Cecr2GT45Bic shows a neural tube defect phenotype and FVB/N in which Cecr2Gt45Bic does not manifest neural closure defects. The second was to idenify strain specific expression differences present during neural closure of the mouse embryo between BALB/cCrl and FVB/N in order to identify candidate modifiers of the Cecr2Gt45Bic neural tube defect. Relevant abstracts are included below. The initial study ; BACKGROUND: Over 200 mouse genes are associated with neural tube defects (NTDs), including Cecr2, the bromodomain-containing subunit of the CERF chromatin remodeling complex. METHODS: Gene-trap mutation Cecr2Gt45Bic results in 74% exencephaly (equivalent of human anencephaly) on the BALB/c strain. Gene expression altered during cranial neural tube closure by the Cecr2 mutation was identified through microarray analysis of 11–14 somites stage Cecr2Gt45Bicembryos. RESULTS: Analysis of Affymetrix Mouse 430 2.0 chips detected 60 transcripts up-regulated and 54 transcripts down-regulated in the Cecr2Gt45Bic embryos (fold > 1.5, p < 0.05). The Cecr2 transcript was reduced only ∼7- to 14-fold from normal levels, suggesting the Cecr2Gt45Bic is a hypomorphic mutation. We therefore generated a novel Cecr2 null allele (Cecr2tm1.1Hemc). Resulting mutants displayed a stronger penetrance of exencephaly than Cecr2Gt45Bic in both BALB/c and FVB/N strains, in addition to midline facial clefts and forebrain encephalocele in the FVB/N strain. The Cecr2 transcript is reduced 260-fold in the Cecr2tm1.1Hemc line. Subsequent qRT-PCR using Cecr2tm1.1Hemc mutant heads confirmed downregulation of transcription factors Alx1/Cart1,Dlx5, Eya1, and Six1. CONCLUSIONS: As both Alx1/Cart1 and Dlx5 mouse mutations result in exencephaly, we hypothesize that changes in expression of these mesenchymal/ectodermal transcription factors may contribute to NTDs associated with Cecr2. Birth Defects Research (Part A), 2010. 010 Wiley-Liss, Inc. The second study: ABSTRACT:Although neural tube defects (NTDs) are common in humans, little is known about their multifactorial genetic causes. While most mouse models involve NTDs caused by a single mutated gene, we have previously described a multigenic system involving susceptibility to NTDs. In mice with a mutation in Cecr2, the cranial NTD exencephaly shows strain specific differences in penetrance, with 74% penetrance in BALB/cCrl and 0% penetrance in FVB/N. Whole genome linkage analysis showed that a region of chromosome 19 was partially responsible for this difference in penetrance. We now reveal by genetic analysis of three subinterval congenic lines that the chromosome 19 region contains more than one modifier gene. Analysis of embryos showed that although a Cecr2 mutation causes wider neural tubes in both strains, FVB/N embryos overcome this abnormality and close. A microarray analysis comparing neurulating female embryos from both strains identified differentially expressed genes within the chromosome 19 region, including Arhgap19, which is expressed at a lower level in BALB/cCrl due to a stop codon specific to that substrain. Modifier genes in this region are of particular interest because it is syntenic to human chromosome 10q25, the site of a human susceptibility locus. (MANUSCRIPT PENDING SUBMISSION)

Dataset Information

Actomyosin stiffens the vertebrate embryo during crucial stages of elongation and neural tube closure.

Publications

Actomyosin stiffens the vertebrate embryo during crucial stages of elongation and neural tube closure.

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