Parameters controlling transcriptional activation during early drosophila development

Big genes and little genes and deadlines for transcription

“…The first ten cycles occur every eight minutes, and of this eight minutes about five are occupied by events of mitosis. During cycles 11, 12, 13 and 14, the interphase period, and time allotted for transcription, lengthens progressively (4,7,16 minutes respectively) 5,6 . There is only limited transcription prior to cycle 14 (ref.…”

“…There is only limited transcription prior to cycle 14 (ref. 7 ), and the genes that are known to be expressed during these early cycles are predominantly small. One expects -and the paper by Rothe et al confirms -that a large gene would not meet the transcriptional deadline imposed by these early rapid mitoses.…”

Drosophila PLUTONIUM protein is a specialized cell cycle regulator required at the onset of embryogenesis.

“…We cannot exclude the possibility that ectopically expressed PLU is not active because it requires additional cofactors or posttranslational modification, but we favor the interpretation that PLU is capable only of controlling the specialized S-phase of early embryos. Several unique aspects of DNA replication at this developmental time might necessitate specific regulation: the onset of S-phase is controlled posttranscriptionally (Edgar and Schubiger, 1986), Sphase is extremely rapid (Foe et al, 1993), and replication origins are about 10 times more frequent than in later mitotic cycles (Blumenthal et al, 1973).…”

“…Thus, when ectopically expressed in this developmental context, PLU protein does not appear to be capable of inhibiting S-phase as it does in early embryonic development. (Edgar and Schubiger, 1986). The maternal cell cycle stockpiles, however, may make the oocyte particularly vulnerable to inappropriate DNA replication once the egg has been activated and the meiotic products have entered interphase.…”

“…Thus, the oocyte may require mechanisms to block the restart of the cell cycle after the completion of meiosis to coordinate it with fertilization. In addition, the early S-M cycles differ from archetypal G1-S-G2-M cycles because the regulation is exclusively posttranscriptional (Edgar and Schubiger, 1986). The shared syncytial cytoplasm implies there are special mechanisms to maintain polar body arrest while the zygotic nuclei replicate and divide.…”