14/ drosophila neurogenesis

Question 1

true or false: fly and vertebrate neurons are different

Answer 1

false

Question 2

where does neural tube develop in vertebrates

Answer 2

• v: dorsal side (spinal cord)

Question 2

why might the d/v axis be inverted between arthropods (flies) and vertebrates

Answer 2

• bone morphogenetic protein BMP and decapentaplegic signal Dpp inverted: (ligands)
• important for patterning dorsal in drosophila
• and ventral in vertebrates
• evolved rotation somehow, signalling pathway predates rotation
• genes are largely homologous when inverted between the groups

Question 2

what is a proneural cluster

Answer 2

• single neurons are selected from a group of largely equivalent cells called a proneural cluster
• not all cells in the fly ectoderm will become neurons, some remain ectodermal
• this uses process of lateral inhibition

Question 3

process of lateral inhibition

Answer 3

• stops all ectodermal cells becoming neurons. cells interact w each other to decide pathways
• the achaete/scute genes set up a cluster called proneural genes
• the notch/delta signalling pathway ensures selection of a single cell of the cluster
• achaete scute proteins promote delta expression
• delta is a transmembrane ligand - can only influence neighbouring cells
• delta binds and activated notch receptor
• small difs in delta expression
• strong notch signal downregulates achaete/scute, these small differences will become amplified
• high achaete/scute expression activates neural genes, losing cell reverts to epidermal fate

Question 3

how many proneural clusters per segment

Answer 3

8, so 8 neuroblasts need to be defined

Question 3

what would notch deficiency cause

Answer 3

more neurons

Question 4

what happens after selection of a neuroblast

Answer 4

• it generates a number of neuronal and glial cells in the process of asymmetric cell division
• neuroblast drops down from the epithelium into interior of embryo
• all cells in drosophila epidermis have an inherent apico-basal polarity (know what’s inside and out), neuroblasts remember this
• memory consists of localised protein complex bazooka (par3 in mammals) and insc/pins are part of this
• protein complex directs localisation of proteins and rnas to opposite poles of cell and orients mitotic spindle. numb important in this
• we then have stem cells, which divide into neuroblasts or ganglion mother cells
• these divide into neurons or glia

Question 5

example of where else asymmetric cell division is used

Answer 5

• to specify adult sensory neurons
• sensory organ precursor divides asymmetrically w numb to one side
• divides into smaller numb side IIb, which becomes socket cell, and larger IIa, which becomes sensory neuron sheath

Question 6

embryonic cerebral cortex development (vertebrates)

Answer 6

• mPar3 regulates s phase and mitosis of a stem cell (runs through entire length of cortex and connects both sides of neural tube)
• after telophase, high notch levels inhibit specialisation
• then low notch allows asymmetric cell division into a neuron for example