The division and differentiation of Drosophila cystocytes

Journal of Morphology - Tập 121 Số 1 - Trang 55-70 - 1967
Elizabeth A. Koch1, Patricia Smith1, Robert C. King1
1Department of Biological Sciences, Northwestern University, Evanston, Illinois

Tóm tắt

AbstractLight and electron microscopical studies allow a descriptive account to be given of he morphogenesis of the egg chamber of Drosophila melanogaster. The study demonstrates that the mitotic products of a single cystoblast generate a branching chain of 16 inter‐connected cystocytes. Two specific cystocytes enter meiotic prophase, while the rest become nurse cells. The two pro‐oocytes form synaptinemal complexes in their nuclei. However, one of the two cells later switches back into the nurse cell developmental pathway. The elongation of the synaptinemal complexes is described, and estimates are made of the time involved in their formation. These complexes continue to be synthesized long after the DNA replication which gives the oocyte its 4C DNA content. This finding implies that at least some genetic crossing over follows DNA replication. Evidence is presented that cells undergoing crossing over are most efficient in repairing radiation‐induced chromosomal breaks. Suggestions are given as to the mechanisms by which (1) cell division is inhibited once 16 cystocytes are formed, (2) the future cleavage planes of cystocytes are programmed, (3) the pro‐oocytes are differentiated from nurse cells, and (4) the oocyte is chosen from the twin pro‐oocytes. The contrasting behaviors of the oocyte and nurse cell nucleoli are described. During oogenesis nucleolar synthesis of ribosomal RNAs is suppressed in the oocyte and concurrently stimulated in the nurse cells. It follows that the nurse nuclei are the major sources of the prodigious quantities of ribosomes found in the ooplasm of the mature oocyte.

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Tài liệu tham khảo

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Journal of Morphology

Tập 121 Số 1

55-70

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