Early development depends on the temporal and spatial interplay between maternally supplied material and mRNA and the onset of zygotic gene expression. Maternally encoded mRNAs must be produced, positioned, and degraded [Surdej and Jacobs-Lorena (1998). Mol. Cell Biol. 18:2892–2900]. For example, transcription of the bicoid gene that determines anterior–posterior polarity in Drosophila is maternal. The mRNA is synthesized in the ovary by nurse cells and then transported to the oocyte, where it localizes to the anterior ends of oocytes. After egg deposition, bicoid mRNA is translated and unstable bicoid protein forms a decreasing concentration gradient from the anterior end of the embryo. At the start of gastrulation, bicoid mRNA has been degraded. Consider two models to explain the degradation of bicoid mRNA: (1) degradation may result from signals within the mRNA (intrinsic model), or (2) degradation may result from the mRNA's position within the egg (extrinsic model). Experimentally, how could one distinguish between these two models?

Video transcript

Everybody. Let's take a look at this practice problem together. The absence of bike oid M R N A in Drosophila leads to the absence of blank larval body parts. So to answer this question, we need to know what by coid is. Recall that there is the bike oid protein in Drosophila. And the bike oid protein is responsible for forming the anterior posterior access of the Drosophila embryo. So is the correct answer. A anterior be posterior si dorsal or D ventral. Let's take a look at a Drosophila embryo depicted here on the screen. We have the anterior part of the embryo and the posterior part of the embryo. Now, these orange dots represent by coid, the bike oid protein. So in the Drosophila embryo, there is the concentration gradient of by coin. What that means is that as you go from the anterior pole towards the post cheerier pole, you get a decrease in the concentration of bike oid. So since the protein is more concentrated on the anterior pole, this means that by coid is important in developing the anterior larval body parts. So the correct answer is a anterior. Alright, everybody I hope you found this helpful and I'll see you soon for the next practice problem.