Dorsal Ventral patterning

Question 1

what is the difference between the dorsal and ventral sides of the dorsal?

Answer 1

the dorsal side is smooth and the ventral is prickley

Question 2

what is the ventral patterning molecule?

Answer 2

Dorsal

Question 3

how is Dorsal distributed in the embryo?

Answer 3

uniformly however it is localised in the nucleus in the ventral side of the embryo

Question 4

what are the tissues that need to be patterned in the embryo?

Answer 4

amnioserosa, dorsal ectoderm, lateral ectoderm, neurogenic ectoderm and the mesoderm from the dorsal to ventral axis

Question 5

what genes do dorsal activate?

Answer 5

twist, snail and rhomoid (rhomboid can initially be activated by int levels of dorsal) and int levels also activate short gastrulation gene

Question 6

what does snail do?

Answer 6

inhibits rhomboid to ensure that there are defined areas of gene expression within the embryo dv axis. Snail represses the neurectoderm determinant rhomboid

Question 7

what is the effect of twist?

Answer 7

twist activates itself and snail

Question 8

what does dorsal inhibit?

Answer 8

folloid, decapentagplegic and zerknullt- these genes are restricted to the dorsal area

Question 9

how do twist and snail have an effect on the patterning of the mesoderm?

Answer 9

twist activates mesoderm expression- causes mesoderm invagination- gastrulation- all twist expressing cells go inside. and to activate muscle selector genes such as bagpipe (expressed in skeletal muscle) and tinman (heart)

Question 10

once twist has ingress, what gene is expressed at the most ventral side?

Answer 10

once twist has gone inside, sog is now expressed at the most ventral side of the cell- form ventral eleemnts of the drosophila neuroblasts which invaginate

Question 11

how do the expression of ventral genes cause the patterning of the neuroblasts?

Answer 11

at different expressions of sog, vnd, ind and msh is expressed in that order. these cause neuroblasts to enlarge them delaminate- there are three waves of this: the first occurs in vnd expressiong areas (those that recieve the most sog) then in the ind then in the msh. the timing of the delamination of the neuroblasts determines their fate.
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Question 12

what is topped and gurken?

Answer 12

tropedo is a gene found in the folic cell and codes for the receptor for gurken- a gene expressed in the oocyte - they allows the follicle cell and the oocyte to communicate

Question 13

what do intermediate levels of dorsal activate?

Answer 13

Intermediate levels of Dorsal activate short gastrulation and repress dorsal determinats such as decapentaplegic, tolloid and zerknult

Question 14

what does zerknult pattern?

Answer 14

Zerknult directs the development of the aminoserosa

Question 15

where is dip expressed?

Answer 15

dorsally

Question 16

how do interactions between the dorsal proteins and ventral proteins pattern the embryo?

Answer 16

Interactions between Dpp sog and tolloid create gradients in the prospective ectoderm that have been shown to regulate the development of different subdomains within the central nervous system.

Question 17

what is the maternal gene that determines DV patterning?

Answer 17

gerkin- it is transported from the nurse cells into the oocyte

Question 18

how do gherkin and torpedo interact?

Answer 18

The binding of Gurken to Torpedo induces the follicle cells to send a message back to the oocyte leading to the re-organsation of the oocyte cytoskeleton. OOcyte microtubules line up with their minus ends anterior and thie plus (growing) ends posterior. T

Question 19

how do the newly formed microtubules (after torpedo signalling) determine dv patterning?

Answer 19

The oocyte nucleus migrates anteriorly along the microtubues bringing a cloud of Gurken protein with it. In its new anterior location Gurken acts to dorsalise the overlying follicle cells.

Question 20

how does the positioning of the nucleus and the gherkin that is released define the dv axis via dorsal?

Answer 20

Gurken-torpedo action in the dorsal follicle cells inhibits the synthesis of Pipe. The gurken signal is short range and does not affect the ventral follicle cells. Pipe synthesis in these cells complexes with an unknown factor and the complex is sectreted into the perivitelline space where it initiates a series of serine proteases (Gastrulation defective, Snake and Easter) to cleave and activate one another. The final protease in the chain, Easter, cleaves
and thereby activates the precursor of the Toll ligand, Spatzle. Activated Spatzle binds to the Toll receptor on the oocyte membrane causing the cytoplasmic kinases Tube and Pelle to phosphorylate. Unphosphorylated Cactus protein is bound to Dorsal holding it in the cytoplasm. Phosphorylation of Cactus causes it to release Dorsal. Unbound, phosphorylated Cactus is degraded and Dorsal enters the nucleus.

Question 21

how is the position of the nerve cord in arthropods and annelids relevant?

Answer 21

n arthropods and annelids nerve cord is ventral and the heart dorsal while in vertebrates the nerve cord is dorsal and the heart ventral. The idea that a vertebrate might be considered an upside-down invertebrate was first proposed in 1822 by the French naturalist Etiene Geoffroy St-Hilaire. The finding that the Drosophila dorsal determinant (Dpp) and the vertebrate ventralralising factor Bmp4 were members of the same growth factor family seemed to vindicate Geoffroy’s hypothesis

Question 22

how are the dorsal ventral patterning elements conserved but play a different biological role?

Answer 22

The Toll, pelle, cactus and dorsal genes all have mammalian counterparts (TRL 2-4, IRAK1, IκΒ and NF-κΒ), which interact in a similar way but play no role in dorso-ventral patterning during embryogeneis. Instead they regulate the innate immune response to bacterial or fungal infection. In flies the Toll pathway plays a similar role in immune defense. It is possible that immunity was the original function of this pathway but that in Drosophila the ‘tool-kit has been co-opted for dorso-ventral patterning, ie, patterning is a derived function.

Question 23

how is the pathway seen in dros seen also in vertebrates?

Answer 23

in drosophilla dpp (TFGbeta family) is expressed dorsally and sog ventrally
the homologous copy of dpp is BMP4 which acts as a ventral morphogen and chordin is dorsally
dpp/ bmp4 activates the genes specifying regions of the CNS in the same order and can substiture for one another transgenic flies/ mice.