BISC 333 Midterm 1 - Drosophilla

Imaginal Discs

-Give rise to adult structures

-Patterened during embryogenesis

-Don't appera till later so if anything goes wrong in patterening it will affect the final product

Cleavge divisions

-Are rapid and synchronous

-Occur in syncytium ( only nuclei diivde)

9 divisions

nuclei move to periphery

12 divisions

-membranes grown in from the periphery and the blastoderm becomes cellular after 13 rounds

-15 pole cells at posterior are set aside and will later form germ cells

Gastrulation

-Mesoderm invaginates on ventral side, fist forminga tube

-gut form 2 invagination on both sides of embryo

Neuroblasts

-Nervous system starts to form when neuroblasts delaminate from ventral ecyoderm

What are the 2 major axis

Anterior-Posterior

Dorsal-Ventral

Segments

3- thoracic

8 -Abdominal

Oocyte

-egg chamber

-signals from older egg chamber polarize younger ones

Bicoid mRNA

-Produced by nurse cells

-Localized to anterior end

Nanos mRNA

-Produced by nurse cells

-Localized to posterior end

Maternal effect genes

-The genotype of the mother determines the phenotype of the embryo

Dorsal-Ventral axis formation

-Gurken prevents synthesis of pipe on the dorsal side

-The formation and activation (by cleaving) of the recptor toll

-Triggers the degradation of Cactus protein and allows the translocation of the dorsal protein into nucleus

What specifiec along the dorsal- ventral axis

Genes are activated/repressed by different concentration of dorsal protein, leading to different fates along the axis

What is a dorsalized/ventralized embryo

Dorsalized -dorsal structures where ventral structure would form

Ventralized- ventral strcuture where dorsal structure would be

Dorsal acts like a morphogen

-dorsal will act like a morphogen to establish different fates along d-v axis

-acts like a transcription factor and activates or represses different target genes at different concentrations specifying for mesoderm and neuroectoderm

Dorsal Morphogen gradients

High - Rhomboid and snail can both bind

(snail represses rhomboid)

Low Concen- Only high affinity sites are able to bind so (rhomboid)

Dpp

-protein and morphogen

-confined only to dorsal due to Dorsal protein and Sog

-Specifies form amnioserosa and dorsal ectoderm

Ventral fate

Controlled by dorsal protein

toll recptors bind to toll ligands which causes the degradation of catctus which releases dorsal protein into the nucleus which acts like a morphogen. when at high concensnail and rhomboid will bind but snail will repress rhomboid when low concentration only rhomboid will bind

Bicoid protein

Anterior protein

-Forms a gradient due to being able to diffuse freely through syncytium

-Bicoid causes the formation of anterior structure wherever it is placed

-prevents translation of Caudal

-transcription factor to activate anterior genes (hunchback)

-translational repressor to suppress posterior genes (caudal0

Caudual

Posterior protein

-responsible for the formation of abdominal structures

-form gradient with high concentration at the posterior end

-transcription factor and activates posterior genes

Nanos

Posterior protein

-Prevents translation of hunchback

-Translational repressor to suppress anterior genes

(hunchback )

Hunchback

-form gradients

-defines the expression of kruppel

Gradient to a stripe

-Hunchback forms a gradient as it diffuses toward the posterior end

-Hunchback can act as a repressor and activator for the same gene at different concentrations ( not activated when too high or low )

-Means kruppel is only specified in a specific window

Kruppel

-Gap gene

-helps establish the a-p segment patterning formation

-gap genes work together to activate pair rule genes

-Kruppel mutant embryos are missing, kruppel expression domains and this mutation is lethal

Even skipped

-pair rule gene

-expression is initally broad then becomes confine to 7 stripes

-activator and repressor confine the expression

-activators and repressors are generally maternal or gap genes

-Repressors limit the expression domain since activators are broadly expressed

-transiently expressed in developing embryo

-Even skipped display hal the number of denticle bands

Parasegments

-transient subdivisions that occur in the Drosophila embryo prior to the formation of segments

-One psterior part and one anterior part

How to make pair rule stripes

-activator and repressor binding sites for gap genes

-enchancer elements for each eve stripe

-LacZ=reporter gene

Gap genes activate primary pair rule which will activate secondary pair rule genes

parasegment border

-a feedback loop involving Wg and Hh signaling establishes the parasegment border

-Loss od Wg leads to the loss of segment polarity. genes normally expressed in posterior part of segment are lost means cells apodt and anterior fate

Wigngless signal tarnsduction pathway

when wnt is present them Bcatein degradation is inhibited and accumulates

Compartment

boundaries to restrict the movement of cells

Summary-Segment formation

-maternal genes activate gap genes

-gap genes in combination activate pair rule genes

-pair rule genes define parasegments and together with gap genes establish their identity

-Segmentation genes establish segment borders and fix them so they are permentantly expressed

Flow of a-p patterening genes

maternal -->gap genes -->pair rule genes-->segment polarity and segment identity

Hox genes

-specifify parasegemtn identty

- all hox genes are homebox transcription factors

-conserved throughout animals

-initial expression is established by gap and pair rule genes, maintainance of expression depends on Polycomb genes

The bithorax comples

-differences in expression levels in part determin parasegment indentity

-darker colour +higher expression

-Bithorax xomplex specifies PD 5-14

-The antennapedia comples specifies PS 1-4