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Teratogenic development in chicken embryos associated with a major deletion in the rRNA gene cluster
Author(s) -
Delany M. E.,
Taylor R. L.,
Bloom S. E.
Publication year - 1995
Publication title -
development, growth and differentiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 66
eISSN - 1440-169X
pISSN - 0012-1592
DOI - 10.1046/j.1440-169x.1995.t01-3-00007.x
Subject(s) - gastrulation , biology , embryo , ribosomal rna , primitive streak , embryogenesis , morphogenesis , andrology , microbiology and biotechnology , gene , genetics , medicine
A new strain of chickens (mPNU) that segregates a severely deleted rDNA cluster was studied. Individuals heterozygous (+/ p 2 ) and homozygous ( p 2 / p 2 ) for the deletion were found to have 56 and 27%, respectively, of the normal complement of rRNA genes (290 copies/cell). Morphogenesis, cellular rRNA levels, and nucleolar sizes, were investigated and compared in normal +/+, +/ p 2 , and p 2 / p 2 embryos. Cellular rRNA contents were similar among the three genotypes at stage X, but subsequently during gastrulation, p 2 / p 2 levels were reduced to 56% and eventually to 43% of +/+. Viability and morphogenesis were normal in p 2 / p 2 embryos until the initial primitive streak stage of gastrulation. However, further development was abnormal and characterized by disrupted axis formation. In +/+ and +/ p 2 embryos, rRNA levels and nucleolar sizes increased during early development; however, the profile of these increases differed temporally and quantitatively between the genotypes. The +/ p 2 embryos, at the full streak stage of gastrulation, exhibited reduced rRNA levels and nucleolar sizes (80% of +/+), yet the +/ p 2 embryos developed normally. These studies establish a minimum copy number requirement lower than previously demonstrated, that is, a rDNA genotype with only 56% of the normal gene complement (∼160 genes) is compatible with early embryonic viability. Also, a rRNA threshold was detected: rRNA levels that were 56% of +/+ failed to support normal gastrulation; however, even under the circumstance of reduced rRNA levels (43% of control), some aspects of gastrulation apparently continue (cell migration and invagination). The teratogenic development of p 2 / p 2 embryos is a biological consequence unique from that found in other metazoan models of rDNA‐deficiency, and will be useful as a model to investigate mechanisms of vertebrate gastrulation and axis formation.