Biology 1001A Lecture Notes - Lecture 11: Apoptosis, Rna Interference, Ecdysone
7 May 2018
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Main Stages of Drosophila Development
1) Mothers pack eggs with organelles (mitochondria) and goodies (mRNAs and proteins) that babies need as soon
as they are fertilized
2) Egg is fertilized and nucleus begins to divide while cell does not. This results in a multinucleate cell.
3) When there are enough nuclei, they migrate to the periphery of the cell which forms blastula: hollow ball of
cytoplasm with nuclei on periphery (the skin is called cellular blastoderm).
4) The blastula turns into gastrula via gastrulation.
5) Gastrula becomes segmented and the segmented parts of the gastrula represent parts of the adult fl’s od
Maternal Effect Genes, Segmentation Genes, Homeotic Genes
- Maternal Effect Genes: genes that are transcribed in the mother during egg formation and the mRNA is packed
into the egg where it is translated; these genes control egg/embryo polarity because the egg (and nuclei in the egg)
need to know which side of the larvae they are on.
- Bicoid: responsible for front + back / anterior + posterior development
- Gurken: responsible for top + bottom / dorsal + ventral development
*Bicoid and Gurken proteins are transcription factors of segmentation genes
How Bicoid and Gurken allow nuclei to determine their location in the embryo
- It is possible for mothers to pack their eggs on one end w/ mRNA. Mothers put Bicoid mRNA into head-
end(anterior) of their eggs. This Bicoid mRNA just sits there w/out being translated (due to masking proteins).
- When egg is fertilized, the masking proteins are degraded and the Bicoid mRNA can be translated. The Bicoid
protein is concentrated at the head-end (anterior) of the egg and absent from the tail-end (posterior) which forms
a Bicoid protein gradient. The Bicoid at the head end tells the nuclei where they are in the embryo.
- Ex. If the nuclei do’t ko hee the ae i the laae, the detet the concentration of Bicoid protein - the
more Bicoid protein that is detected, the closer the nuclei is to the head-end Gurken also works this way,
except the higher the concentration of Gurken protein, the closer the nuclei are to the top (back/dorsal) of the
larvae.
- Segmentation Genes: genes that divide the embryo into segments that become eyes, wings, legs, etc.; the protein
products of maternal effect genes are transcription factors of these genes and these genes are under the control of
homeotic genes
1. Gap Genes subdivide the embryo along the anterior-posterior axis into broad regions
2. Pair-rule Genes further divide embryo into units of 2 segments each
- Homeotic Genes: have a homeobox (DNA) that codes for a DNA-binding homeodomain (transcription factors)
that does’t id to the hoeoo ut to a egio i the pootes of the segetatio gees hose
transcription is regulated by certain homeotic genes
How do Homeotic Genes Regulate Development?
- Homeotic Genes determine what structures are formed in a given segment - if a given segment is supposed to
grow legs, it is the homeotic genes that do this
- Homeotic Genes encode transcription factors that regulate the expression of whole host of genes needed to
make a particular adult structure - if you collect all genes controlling a segment, you will find that they have the
same homeobox
- Certain homeotic genes are activated in specific segments to create segment specific structures. For example, a
utatio i atea a hoeoti gee aused legs to go out of the dosophila’s head.
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Document Summary
Main stages of drosophila development: mothers pack eggs with organelles (mitochondria) and goodies (mrnas and proteins) that babies need as soon as they are fertilized, egg is fertilized and nucleus begins to divide while cell does not. Bicoid: responsible for front + back / anterior + posterior development. Gurken: responsible for top + bottom / dorsal + ventral development. *bicoid and gurken proteins are transcription factors of segmentation genes. How bicoid and gurken allow nuclei to determine their location in the embryo. It is possible for mothers to pack their eggs on one end w/ mrna. Mothers put bicoid mrna into head- end(anterior) of their eggs. This bicoid mrna just sits there w/out being translated (due to masking proteins). When egg is fertilized, the masking proteins are degraded and the bicoid mrna can be translated. The bicoid protein is concentrated at the head-end (anterior) of the egg and absent from the tail-end (posterior) which forms a bicoid protein gradient.
