A cytochemical study of the relationship between RNA synthesis and hemoglobin synthesis has been performed on splenectomized newts, Triturus viridescens. Employing radioautography, labeled cytidine was incorporated into the RNA of the early developmental stages but was not incorporated in the later stages. Labeled leucine was incorporated into the cellular protein of all stages except mature erythrocytes but was incorporated at a higher level in the later stages. Microphotometric measurements of azure B binding to cytoplasmic RNA revealed a sharp initial increase between the stem cell and proerythroblast followed by a rapid decrease between the basophilic and polychromatophilic stages. The loss of cytoplasmic RNA became more gradual in the late stages and, in the mature erythrocyte, little or no cytoplasmic RNA could be detected. Measurements of cytoplasmic total protein, using fast green staining at pH 2.0, and of heme showed that both curves increased similarly with development, indicating net hemoglobin synthesis. The results are compatible with the hypothesis that, as the stem cell differentiates along erythrocytic lines, a stable "messenger" RNA specifying the production of a given type or types of hemoglobin is formed. This complex probably becomes associated with ribosomal RNA and is retained throughout the process of RBC differentiation.

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