Oxidation-Reduction Indicator Patterns in the Development of Clavellina huntsmani

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Abstract
A study of intracellular developmental pattern by means of the indophenol reaction, intracellular oxidation of methylene blue and Janus green, reduced by sodium hydrosulfite, reduction of indophenol and oxidized dyes by hydrosulfite and reoxidation of these indicators following reduction. The indophenol reagents were used in very much lower concn. than in the Nadi reaction and low dye concns. were also used, so that intracellular oxidations and reductions occurred while the material was still living. From very early oocyte stages there is an oxidation-reduction gradient of indophenol and of oxidized and reduced dyes. Nuclear position is somewhat variable but, at least in later oOcyte stages and full grown eggs, the nucleus is usually in or near the region of greatest reactivity. The most conspicuous feature of pattern following fertilization is appearance of a region of very great reactivity in oxidation and reduction of indicators in the posterior region of the egg, as observed in earlier studies. This persists in certain cells through cleavage and into larval development and differentiates chiefly into the muscles of the larval tail. Greater reactivity in the two apical posterior cells than in anterior cells of the 8-cell stage and later, a perinuclear zone of greater reactivity in earlier cleavage, and slight reaction in the cytoplasm of all cells, are other characteristics of the pattern. In the early gastrula before elongation of the tail begins, reactivity increases in the prospective tail ectoderm and to a lesser degree in the neural plate and still less in regions lateral to the blastopore. The intensely reacting mesoderm cells appear in longitudinal rows, increasing in length by continued division. With beginning elongation of the tail further increase in reactivity occurs in the tail ectoderm with a gradient decreasing from the tip. A region, varying in length at the tip of the tail may secondarily reduce intracellular indophenol and oxidized dyes without external oxygen decrease. With differentiation of the muscles of the tail their reactivity decreases some-what. In the larval body reactivity decreases from the dorsal region. With increase in intracellular concn. of indophenol and of oxidized dyes, toxic effect becomes evident in differential retardation or absence of reduction. Susceptibility to toxic effect decreases with decrease in original reactivity so that there may be more or less reversal of the pattern differentials as the intracellular concns. of indicators become toxic. Absence of sharp boundaries in the regions of differing reactivity indicates that the pattern of Clavellina is in some degree quantitative rather than a pattern of strictly qualitative regional differences.

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