BIOMG 1350 Lecture Notes - Lecture 21: Blastoderm, Trithorax-Group Proteins, Antennapedia
18 Dec 2016
School
Department
Course
Professor
● A gene regulatory cascade specifies segments
○ Egg Polarity Genes: anterior gradient, before maternal to zygetoci transition
○ Gap Genes: Broad overlapping bands; synctial blastoderm
○ Pair-rule Genes: seven stripes (define segment boundaries), syncial blastoderm
○ Segment polarity genes: fourteen stripes (subdivide segments into smaller
domains), cellular blastoderm
● Dissecting the regulatory region of the pair rule gene Eve
○ Stripe 2 Regulatory segment
■ (Lac Z gene expressed only in stripe 2)
■ ~480 base pairs
■ Giant and Kruppel are transcriptional repressors
■ Bicoid and Hunchback are transcriptional activators
■ Bicoid is localized in anterior and has gradient towards posterior
● Same with Hunchback
■ Giant has 2 bands on anterior and posterior
■ Kruppel has 1 localized band in the middle
● Within stripe 2, there are Bicoid and hunchback expressed but not
giant or kruppel
● Only Activators are expressed
● Transcription will be activated
● Maintaining memory after cellularization
○ Segment polarity gene is present into adulthood; the others are transient and
only active during development
○ Signaling feedback loop maintains expression of segment polarity genes
● Homeotic Mutations
○ Homeotic selector genes provide segment identity
■ Mutant larva lacking all the Bithorax genes have 14 identical segments
■ Located in 2 regions
● Antennapedia compelx and bithorax complex
● Homeotic selector genes or HOX genes
● How is expression specified?
○ Egg polarity, gap geens, pair rule and segment polarity all
send signals to determin where hox genes are located
○ What maintains homeotic selector grene expression?
■ Polyccomb group proteins and trithorax group proteins
● Histone modifications
○ Parental nucleosomes with modified histones
■ Half the duaghter nucleosomes inherit the modified parental histones
● Parnetal pattern of histone modification reestablisehd by enzymes
that recognize the same modificcations they catalyze
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Egg polarity genes: anterior gradient, before maternal to zygetoci transition. Gap genes: broad overlapping bands; synctial blastoderm. Pair-rule genes: seven stripes (define segment boundaries), syncial blastoderm. Segment polarity genes: fourteen stripes (subdivide segments into smaller domains), cellular blastoderm. Dissecting the regulatory region of the pair rule gene eve. Stripe 2 regulatory segment (lac z gene expressed only in stripe 2) Bicoid is localized in anterior and has gradient towards posterior. Giant has 2 bands on anterior and posterior. Kruppel has 1 localized band in the middle. Within stripe 2, there are bicoid and hunchback expressed but not giant or kruppel. Segment polarity gene is present into adulthood; the others are transient and only active during development. Signaling feedback loop maintains expression of segment polarity genes. Mutant larva lacking all the bithorax genes have 14 identical segments. Egg polarity, gap geens, pair rule and segment polarity all send signals to determin where hox genes are located.
