Biol168_10F_Lecture 7_8Oct2010

Biol168_10F_Lecture 7_8Oct2010 - Dr. Morris Maduro, UC...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 7, page 1 Lecture #7: Drosophila : Segment Polarity and Homeotic Genes Text: 2nd Ed.: 175-177; 181-188. 3rd Ed.: 67-73; 78-85. Some figures in these notes are redrawn from Wolpert et al. (2nd edition). Segment polarity genes The transient prepatterning that is established by the gap and pair-rule genes must give way to activities within cells as the embryo moves from syncytial to cellularized. The final stage of refinement of cell fates is to specify regions within each parasegment. This is accomplished by the segment polarity genes (6 known). Segment polarity mutants have the normal number of segments, but part of each segment is deleted and replaced with a mirror-image duplication of the remainder. Hence, these genes do not establish the identity of segments, but rather the pattern within each segment. For example, on the right is shown the pattern of denticle belts in a wild-type and gooseberry segment polarity mutant. The segment polarity genes mark the first genes expressed to be involved in cell-cell signaling. As such, only two genes are transcription factors ( engrailed and gooseberry ); the remainder are involved in signal transduction. The region-specific expression and activity of the segment polarity genes involves several stages. First, the expression patterns of the pair-rule genes are refined from a sine-wave ON-OFF pattern into a set of repeating gradients through interactions with other pair-rule gene products (i.e. ftz , hairy and runt ). This results in a polarization of eve expression – miniature gradients within each parasegment. Eve works with another pair-rule gene, fushi tarazu ( ftz ; “too few segments” in Japanese), whose expression (even numbered parasegments) is complementary to that of eve (odd numbered parasegments). Like eve , its expression becomes refined in the complementary parasegments. High levels of eve or ftz result in activation of the transcription factor engrailed ( en ) in the anteriormost cell of each parasegment . The result of this is the generation of 14 engrailed stripes in which e ngrailed expression marks the anterior boundary of each parasegment. Immediately anterior to en -expressing cells, the secreted protein
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

Biol168_10F_Lecture 7_8Oct2010 - Dr. Morris Maduro, UC...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online