Experimental manipulation of the mammalian embryo: biological and genetic consequences.
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The relationship between growth rate and regionalization of amphibian, bird and mammalian embryos is briefly reviewed. In contrast to the others, mammals start gastrulation with few cells but accelerate cell proliferation coincidentally. Experiments are described which demonstrate (1) autonomous development of pieces isolated surgically from such mouse embryos, and (2) an absence of regeneration or regulation. Since such embryos regulate completely after chemically induced random cell death it is postulated that these results reflect developmental determination and a resulting mosaicism that suggests development may have a clonal basis. Maps are drawn, allocating positions to various tissues in the embryo.
Primitive streak
Developmental Biology
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Journal Article Formation of Nucellar Embryos with Total Absence of Embryo Sacs in Two Species of Gramineae Get access C. SHANTHAMMA, C. SHANTHAMMA Department of Botany, University of MysoreManasa Gangotri, Mysore 570006, S. India Search for other works by this author on: Oxford Academic PubMed Google Scholar K. N. NARAYAN K. N. NARAYAN Department of Botany, University of MysoreManasa Gangotri, Mysore 570006, S. India Search for other works by this author on: Oxford Academic PubMed Google Scholar Annals of Botany, Volume 41, Issue 2, March 1977, Pages 469–470, https://doi.org/10.1093/oxfordjournals.aob.a085314 Published: 01 March 1977 Article history Received: 13 August 1976 Revision received: 25 October 1976 Published: 01 March 1977
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In vivo, embryos which are homozygous for the t6 mutation die during egg cylinder development (gestation days 5.5--6.5). In vitro, these mutant embryos can be distinguished from their wild-type littermates by their developmental arrest and by the failure of their trophoblast cells to transform to giant cells. We have investigated the nature of this lethality by constructing triploid embryos with varying combinations of the t6 mutant chromosome. The phenotypes of outgrowths from these triploid embryos were examined and compared with the phenotypes of outgrowths from +/+, +/t6, and t6/t6 embryos. The data show 1) that +/t6/t6 embryos are phenotypically wild-type, while t6/t6/t6 embryos are phenotypically mutant and 2) that t6/t6/t6 and t6/t6 embryos are developmentally arrested at the same stage of outgrowth.
Trophoblast
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Arabidopsis DNA hypomethylation mutation, ddm1 , results in a variety of developmental abnormalities by slowly inducing heritable lesions at unlinked loci. Here, late‐flowering traits observed at high frequencies in independently‐established ddm1 lines were genetically characterized. In all of the four late‐flowering lines examined the traits were dominant and mapped to the same chromosomal region, which is close or possibly identical to the FWA locus. The ddm1 ‐induced phenotypic onsets are apparently not random mutation events, but specific to a group of genes, suggesting the underlying epigenetic mechanism. The DNA methylation mutant provide useful system for identifying epigenetically‐regulated genes important for plant development.
RNA-Directed DNA Methylation
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ABSTRACT The size of the inner cell mass and egg cylinder was estimated in mouse embryos derived from the aggregation of two 8-cell stages and in control ‘single’ embryos. The comparison suggests that growth regulation in the ‘double’ embryos takes place fairly rapidly, after the formation of the egg cylinder but before the appearance of the pro-amniotic cavity.
Inner cell mass
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Coelom
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Despite the fact that a variety of experimental techniques have been devised over the years to induce tetraploid mammalian embryonic development, success rates to date have been limited. Apart from the early study by Snow, who obtained development to term of a limited number of cytochalasin B-induced tetraploid mouse embryos, no other researchers have achieved development of tetraploid embryos beyond the early postimplantation period. We now report advanced postimplantation development of tetraploid mouse embryos following electrofusion of blastomeres at the 2-cell stage, and subsequent transfer of these 1-cell 'fused' embryos to appropriate recipients. Cytogenetic analysis of the extraembryonic membranes of all of the postimplantation embryos encountered in the present study has provided an unequivocal means of confirming their tetraploid chromosome constitution. A preliminary morphological and histological analysis of the tetraploid embryos obtained by this technique has revealed that characteristic craniofacial abnormalities particularly involving the forebrain and eyes were consistently observed, and these features were often associated with abnormalities of the vertebral axis and heart. The most advanced viable embryo in this series was recovered on the 15th day of gestation, and its morphological features suggest that it was developmentally equivalent to a normal embryo of about 13.5-14 days p.c.
Electrofusion
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Des recherches recentes effectuees dans de nombreux laboratoires ont permis de mettre en evidence les interactions morphoganes qui s9exercent entre les deux composants, epithelial et mesenchymateux, d9une jeune ebauche en cours de differenciation. Ces travaux, utilisant la technique de digestion partielle par la trypsine qui permet de dissocier une jeune ebauche en ses deux composants (Moscona, 1952), confirment les resultats obtenus par Grobstein (1953, 1955)sur les glandes salivaires et le metanephros de l9embryon de souris. Us etablissent les faits suivants: Chaque element, epithelial ou mesenchymateux, d9une jeune ebauche determinee ne se differencie pas a l9etat isole, qu9il soit cultive in vitro (Auerbach, 1960; Dameron, 1961; Calame, 1961; Sigot, 1962), ou greffe sur la membrane chorio-allantoidienne de l9embryon de Poulet (Calame, 1961). La reassociation des deux elements entre eux permet la differenciation de l9ebauche. Des associations heterologues d9epithelium avec des mesenchymes d9organes differents permettent de tester la specificite des interactions demontrees.
Chorioallantoic membrane
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