TY - JOUR
T1 - Molecular aspects of chromatin elimination in Ascaris lumbricoides
AU - Tobler, H.
AU - Smith, K. D.
AU - Ursprung, Heinrich
N1 - Funding Information:
This work was supported by a fellowship from the Swiss Medical Academy (H.T.), and by National Science Foundation Grants no. GB-E-597 (K.D.S.) and GB-7803 (H.U.). We thank Dr. D. D. Brown for providing labeled Xenopus rRNA and for much personal advice. The collaboration of Dr. E. N. Moudrianakis in the electron microscope part is gratefully acknowledged. Drs. H. Bielka and J. Grummt (Berlin) provided valuable advice.
PY - 1972/2
Y1 - 1972/2
N2 - DNA from spermatids, 4-cell stages, and larvae of Ascaris lumbricoides was isolated, and the genome size before and after chromatin elimination was determined by isotope dilution. According to these determinations, 27% of the DNA is lost during the process of chromatin elimination. This value is based on the assumption that larval nuclei are diploid. The genomes were then characterized by CsCl equilibrium density gradient centrifugation and renaturation kinetics. The eliminated DNA does not differ from the retained DNA in base composition. About 26% of the DNA of 4-cell stage embryos sediments as a light satellite and was shown to be mitochondrial DNA by electron microscopy. Renaturation kinetics revealed that 10% of the retained somatic DNA is repetitious with an average family size of 5500 to 7000 copies, whereas 90% of the retained DNA is presumably composed of unique sequences. By contrast, germ-line DNA contains 23% fast renaturing DNA with a family size of 7000 to 10,000 copies. Thus, eliminated DNA consists of repetitious and unique sequences in a ratio of about 1:1. Hybridization experiments of heterologous rRNA to 4-cell stage and larval DNA have shown that the eliminated DNA is not selectively enriched for ribosomal DNA. The results are consistent with the assumption that eliminated DNA does not comprise any rDNA cistrons. Studies with complementary RNA indicate that the eliminated DNA contains repetitious DNA sequences that are not present in the somatic repetitious DNA.
AB - DNA from spermatids, 4-cell stages, and larvae of Ascaris lumbricoides was isolated, and the genome size before and after chromatin elimination was determined by isotope dilution. According to these determinations, 27% of the DNA is lost during the process of chromatin elimination. This value is based on the assumption that larval nuclei are diploid. The genomes were then characterized by CsCl equilibrium density gradient centrifugation and renaturation kinetics. The eliminated DNA does not differ from the retained DNA in base composition. About 26% of the DNA of 4-cell stage embryos sediments as a light satellite and was shown to be mitochondrial DNA by electron microscopy. Renaturation kinetics revealed that 10% of the retained somatic DNA is repetitious with an average family size of 5500 to 7000 copies, whereas 90% of the retained DNA is presumably composed of unique sequences. By contrast, germ-line DNA contains 23% fast renaturing DNA with a family size of 7000 to 10,000 copies. Thus, eliminated DNA consists of repetitious and unique sequences in a ratio of about 1:1. Hybridization experiments of heterologous rRNA to 4-cell stage and larval DNA have shown that the eliminated DNA is not selectively enriched for ribosomal DNA. The results are consistent with the assumption that eliminated DNA does not comprise any rDNA cistrons. Studies with complementary RNA indicate that the eliminated DNA contains repetitious DNA sequences that are not present in the somatic repetitious DNA.
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U2 - 10.1016/0012-1606(72)90097-8
DO - 10.1016/0012-1606(72)90097-8
M3 - Article
C2 - 4553431
AN - SCOPUS:0015293715
SN - 0012-1606
VL - 27
SP - 190
EP - 203
JO - Developmental biology
JF - Developmental biology
IS - 2
ER -