Analysis of Nuclear/Cytoplasm Ratio and Histone Levels at the Midblastula Transition Across Various Species of Drosophila

Abstract

In recently fertilized Drosophila embryos, maternal deposits regulate development, while zygotic transcription is almost nowhere to be found. Over time, the maternal RNAs are degraded and zygotic transcription is activated, in a process known as the maternal to zygotic transition, or MZT. In conjunction with the MZT, the embryo’s progression into cycle 14 induces significant lengthening of the cell cycle. This event is known as the midblastula transition, or MBT, and is strongly regulated by the nuclear-to-cytoplasm ratio, or N/C ratio. To better understand the timing of the MBT, we look at histones as a N/C ratio-dependent inhibitor across various species of Drosophila. Western blots were used to quantify histone levels of each species relative to the model organism D. melanogaster. Histone levels at the MBT, with the exception of a few outliers, remained fairly consistent across species. Images of embryos that we fixed and stained at the MBT allowed us to determine the embryo size and nuclear content for each species. The amount of DNA present in each species at the MBT varied more significantly than histone levels, as was expected due to their known differences in genome size and developmental timing. Future studies will hopefully identify proteins that vary with the N/C ratio rather than egg size alone by analyzing the relationships between total amount of DNA, histone levels, and embryo volume at the MBT.