Chromatoid bodies in somatic cells of the planarian: Observations on their behavior during mitosis

The behavior of somatic cell chromatoid bodies in the planarian Dugesia dorotocephala during mitosis has been studied by electron microscopy. The relatively undifferentiated beta (progenitor) cells are the only somatic cells containing chromatoid bodies and also are the only dividing somatic cells. Somatic cell chromatoid bodies are known to disappear as differentiation takes place and reappear when dedifferentiation occurs. Interphase and prophase beta cells have juxtanuclear and peripheral cytoplasmic chromatoid bodies. There is no ultrastructural evidence to suggest they are derived from formed nuclear material. During metaphase and anaphase, the chromatoid bodies are segregated from the chromosomes and adjacent cytoplasm by cups of double membranes. By the completion of telophase, the chromatoid body size and number immediately adjacent to the nucleus is markedly decreased and extremely large chromatoid bodies may be found further out in the cytoplasm. These findings are compared to the behavior of germ cell chromatoid bodies and discussed in terms of their possible significance and function.