It is well known that animal tissues have the capacity to induce tissue differentiation when they act upon amphibian presumptive epidermis. Recently, many papers have been published concerning separation of the inductive agents from heterogeneous tissues and their distribution in the cell (TIEDEMANN et al., 1956;YAMADA, 1958;KAWAKAMI et al., 1961). According to K~W A K A M I and IYEIRI (1962 a), the neural or archencephalic induction is produced by ribonucleoprotein particles, and the non.ribonucleoprotein fraction isolated from mesoderm-inducing tissues is responsible for the inducing effect of the tissues. Thus distribution of the inductive agents in cytoplasm has been demonstrated, but few papers have referred to the nucleus. This brief note will report data which have been obtained on the distribution of the inductive agents in isolated nuclei.
MATERIALS AND METHODSRat liver nuclei were isolated by the method reported by RENDI (1960). and fractionated by the methods of ALLFREY et al. (1957) with some modification. The nuclei were extracted first with 0.1 M Tris-phosphate buffer (pH 7.1) and centrifuged down at 1,000 g for 10 minutes. The supernatant was termed "neutral buffer extract". The sediment was extracted again with 1 M NaCI, followed by centrifugation a t 26,000 g for 60 minutes, and the supernatant and resulting sediment were termed "1 M NaCl extract" and "residue", respectively. T h e neutral buffer extract was centrifuged a t 105,000 g for 90 minutes and the resulting sediment was termed "nuclear ribosome fraction". The inductive capacities of these materials were tested by on the presumptive epidermis of Triturw hrrhogaster gastrulae. Chemical analysis of RNA was performed by the orcinol method, and DNA was analysed by the diphenylamine method. The samples of isolated nuclei were examined under both light and electron microscopes. For electron microscopical observation, the nucleus samples were fixed by Veronal-buffered osmium tetroxide (pH 7.3, l,q), dehydrated and embedded in n-butyl methacrylate (PALADE, 1952 a).
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