Cytochcmical studies of oocyte growth in the lancelet, Branchiostoma caribaeum

Summary

• 1. The general pattern of RNA and protein yolk synthesis in growing lancelet oocytes was similar to that encountered in most animal groups; i.e., after an initial period of increasing concentrations of cytoplasmic and nuclear RNA, these declined coincident with the initiation of protein yolk synthesis.

• 2. As the cytoplasmic concentration of RNA decreased in late stage one and subsequent stages, a central vacuole appeared in the nucleoli and progressively enlarged. In late stage two and stage three oocytes a filamentous intravacuolar ribonucleoprotein component became particularly prominent in the nucleolus.

• 3. Cytoplasmic and nucleolar staining was obtained with a method for histones; the intensity and distribution of staining paralleled that of RNA, being greatest in stage one and decreasing in subsequent stages. This indicated that the material stained by this method was probably associated with RNA rather than DNA. The possibility that material stained by the histone method in oocytes might be ribosomal protein was discussed.

• 4. Coincident with the elaboration of protein yolk, there was a dramatic increase in the concentration of non-chromosomal karyoplasmic protein. This represents an instance of cytochemically demonstrable nuclear differentiation. The possible developmental significance of this accumulation of nuclear protein in oocytes was discussed.

• 5. During stages two and three a cortical zone of acid mucopolysaccharide material was produced in lancelet oocytes. This cortical zone corresponded both morphologically and cytochemically with the zona radiata of teleost oocytes. The zona radiata of lancelet oocytes was clearly produced by the oocyte rather than the investing connective tissue cells.