Published in: Naturwissenschaften, vol. 52, no. 6, pp. 141-142 (1965).

"Evidence for Inductive Properties of the Micromere-RNA in Sea-urchin Embryos".

Gerhard Czihak

Max-Plank-Institut fur Meeresbiologie, Abt. H. Bauer,
74 Tubingen, Melanchthonstrasse 36, Germany


Immediately before and during the 5th cleavage, only the nuclei in the micromeres synthsize RNA (Fig. 1) as is demonstrated by 3H-uridine incorporation in pulse experiments and subsequent ribonuclease treatment. Labelling is also found in the cytoplasm of the micromeres 20 minutes after the embryos had been transferred to sea-water containing cold uridine (Fig. 2). Then and one hour later all nuclei of the embryo show incorporation of labelled substance. The labelling of the micromeres decreases gradually. No silver grains can be detected in autoradiographs previously treated with ribonuclease and cold perchloric acid. These facts suggest that it is RNA which is transported from the micromeres to the macro- and mesomeres.

As Horstadius [2] has shown, transplanted micromeres induce the differentiation of a secondary archenteron. One may therefore suppose that RNA from the micromeres has inductive properties. This hypothesis is favoured by experiments with 8-azaguanine which is exclusively incorporated into the embryos RNA [1]. 16-cell stages treated with this antimetabolite at the time when micromere-RNA synthesis occurs, are not able to develop the archenteron (Fig. 3). No influences, defects, or transformations of other parts of the embryo have been found. The primary mesenchyme cells are quite normal and even a normal skeleton is formed which indicates that the RNA synthsized in the micromeres is responsible for the differentiation of the archenteron and not for the differentiation of the micromeres into primary mesenchyme cells.

Fig. 1. Meridional section through a 16-cell stage of Paracentrotus lividus immediately after incubation with 3H-uridine

Fig. 2. Analogue section through an embryo transferred into pure sea-water and fixed one hour later: the labelled substance is spreading over the embryo

Fig. 3. 48 hours old embyo (seen from above in optical section) treated for 30 minutes with 8-azaguanine in the 16-cell stage. The archenteron is lacking in the embryo, which is in other respects quite normal (cf. skeleton, pigment cells, thickened oral and lateral ectoderm). Controls are well developed plutei.

This work, supported by the "Deutsche Forschungs-gemeinschaft" will be published at full extent in W. Roux' Arch. Entwicklungsmechan. Organismen  (vol. 156, 504 (1965).

1. Bamberger J.W., W.E. Martin, L.W. Stearns, and  W.B. Jolley: Exptl. Cell Research 31: 266-274 (1963).

2. Horstadius S.: Publ. Staz. Zool. Napoli 14: 251-479 (1935).


Additional Embryo References:

1. Love R, "Distribution of Ribonucleic Acid in Tumour Cells during Mitosis", Nature 180: 1338-1339 (1957).

2. Cowden RR, and Lehman HE, "A Cytochemical Study of Differentiation in Early Echinoid Development", Growth vol. 27, pp. 185-197 (1963).

3. Czihak G, "Entwicklungsphysiologische Untersuchen an Echiniden. Ribonucleinsaure-Synthese in dem Mikromeren und Entodermdifferenzierrung. Ein Beitrag zum Problem der Induktion", Wilhelm Roux' Arch. Entwicklungsmechan. Organismen vol. 156, pp. 504-524 (1965).

4. Hagstrom BE, and Lonning S, "Time-lapse and Electron Microscopic Studies of Sea Urchin Micromeres", Protoplasma vol. 68, no. 3, pp. 271-288 (1969).

5. Czihak G, and Horstadius S, "Transplantation of RNA-Labeled Micromeres into Animal Halves of Sea Urchin Embryos. A Contribution to the Problem of Embryonic Induction", Developmental Biology, vol. 22, no. 1, pp. 15-30 (1970).

6. Kronenberg LH, and Humphreys T, "Double-Stranded Ribonucleic Acid in Sea Urchin Embryos", Biochemistry vol. 11, no. 11, pp. 2020-2026 (1972).


Additional Chromatin References:

1. Frenster JH, Allfrey VG, and Mirsky, AE, "Repressed and Active Chromatin Isolated from Interphase Lymphocytes", Proc. Natl. Acad. Sci., USA, vol. 50, no. 6, pp. 1026-1032 (Dec. 1963):

2. Frenster JH, "Ultrastructural Continuity between Active and Repressed Chromatin", Nature, vol. 205, no. 4978, pp. 1341-1342 (March 27, 1965).

3. Frenster JH, "Nuclear Polyanions as De-repressors of Synthesis of Ribonucleic Acid", Nature, vol. 206, no. 4985, pp. 680-683 (May 15, 1965).

4. Frenster JH, "A Model of Specific De-repression within Interphase Chromatin", Nature, vol. 206, no. 4990, pp. 1269-1270 (June 19, 1965 ).

5. Frenster JH, "Localized Strand Separations within Deoxyribonucleic Acid during Selective Transcription", Nature, vol. 208: no. 5013, pp. 894-896 (November 27, 1965).

6. Frenster JH, "Correlation of the Binding to DNA Loops or to DNA Helices with the Effect on RNA Synthesis", Nature, vol. 208, no. 5015, p. 1093 (December 11, 1965).

7. Frenster JH, "Mechanisms of Repression and De-Repression within Interphase Chromatin", In-Vitro, vol. 1, pp. 78-101 (1965).

8. De Carvalho S, "Effect of RNA from Normal Human Marrow on Leukaemic Marrow In-Vivo".

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