What are the homeobox characteristics?
- contain a highly conserved sequence of 180 nucleotides called the homeobox which codes for the 60 aa homeodomain
- play a major role in vertebrates with regard to cranio-caudal segmentation, not only along main body axis but within the development of many organs
- activated in a 3’ to 5’ direction (opposite of transcription direction)
What are examples of homeobox containing genes?
- Hox
- Pax
- POU
- Lim protein genes
- Dix
What are some mutations in homeobox containing genes?
- loss of function -> result in posterior to anterior transformations
- gain of function -> result in anterior to posterior transformations
What are some groups of genes that contain the homeobox?
- Hox
- entrained
- paired: Pax
- POU
- LIM
- ZF (Zn finger)
- NK-2
What direction are homeobox genes activated?
-3’ to 5’
What are some characteristics of The Tbx(T-box) genes?
- contained a conserved T-box coding 180-200aa
- family includes up to 100 genes
- plays role in inducing mesodermal germ layer and in coordinating the outgrowth of the arm or leg
What are some characteristics of helix-loop-helix genes?
- code for basic helix loop helix transcription factors
- basic regions of proteins bind to DNA
- Helix loop helix involved in homodimerization and heterodimerization
- important in myogenesis
What are some characteristics of Forkhead(Fox) genes?
- type of helix loop helix family
- expressed in many developing organs throughout the body
What are zinc finger transcription factors?
-the proteins have zinc ions bound to polypeptide chain that cause the chain to form finger like projections that can be inserted into the DNA helix
What are some examples of zinc finer transcription factors?
- Sox genes: high mobility group domain that binds to minor groove on DNA helix rather than major groove, includes SRY gene
- WT1: important for the development of the embryonic kidney and the adult kidney. Takes name from Wilms tumor, which is a kidney tumors that develops in children
What are the categories of developmental molecules?
- transcription factors
- signaling molecules
- receptor molecules
What are the different classes of genes that control Drosophilia development?
-egg polarity/maternal effect genes
-segmentation genes
+Gap
+pair-rule
+segment-polarity genes
-homeotic genes
What is the function of maternal effect genes?
-establish gradients from anterior and posterior poles of the egg
What is the function of segmentation genes?
-define broad regions in the egg
What are the functions of pair-rule and segment-polarity genes?
- define 7 segments
- define 14 segments
What is the function of homeotic genes?
- determine regional characteristics
- products of homeotic genes activate other genes that encode segment specific characteristics
What are three protein expressed in the Drosophilia ovary and how do they interact?
- Dorsal
- cactus
- toll
- cactus binds to the dorsal protein and traps it in the cytoplasm
- toll leads to the degradation of the cactus protein, allowing the dorsal protein to move into the nuclei of the ventral cells
What genes in Drosophilia establish dorsal-ventral axis? Anterior-posterior?
Dorsal-ventral:
- dorsal
- cactus
- toll
Anterior-posterior:
- bicoid
- nanos
- hunchback
How are egg polarity genes expressed?
- transcribed into mRNAs in the ovary during egg formation.
- mRNAs migrate into the eggs and are translated into proteins after fertilization
- these genes work by setting up protein gradients
What is a morphogen?
-a protein that varies in concentration and causes different developmental responses as a result of the conc gradients
What do bicoid and nanos proteins do?
- bicoid: responsible for anterior structures, stimulates hunchback
- nanos: responsible for posterior structures, inhibits hunchback
Are segmentation genes maternal genes? Why/
NO! Because they are transcribed after fertilization
What regulates segmentations genes?
-bicoid and nanos
What are the three classes of segmentation genes and what do they do?
- gap genes: delete adjacent segments
- pair-rule genes: delete same part of pattern in every other segment
- segment-polarity genes: affect polarity of segment (ant. Vs post)
