Two Heads Are Better Than One Case Study

dorsal side

what side of embryo does blastopore become

she transplanted DBL cells from one embryo to the opposite side of another embryo → produced 2 DBLS, 2 opposing heads, and formation of 2 separate axes that gave a conjoined organism

what was the experiment that Hilde Proscholdt did

self-determined tissue → capable of organizing the cells around it

the DBL is the only what in the early gastrula

the organizer → they are the primary embryonic organizer

what are dorsal lip cells known as

the dorsal axis and neural tube

what do the DBL cells induce formation of

1) the transplanted DBL induces the host’s ventral tissues to change fate and form a neural tube and dorsal mesoderm tissue

2) organize the host and donor tissues into a primary and secondary embryo, each with clear A-P and D-V axes

what are the 2 reasons shown during the experiment that give the DBL cells its name as the organizer

no → it starts the processes that start a cascade of events that allow for all the organization to occur (aside from dorsal axis)

does the organizer organize everything?

1) initiate gastrulation

2) induce formation of the neural tube

3) self-differentiate into dorsal mesoderm

4) changes the mesoderm surrounding it to form somites

what are the 4 things the organizer does

inhibitors of BMPS

what are chordin and noggin

bone morphogenetic proteins that are expressed through the ectoderm and mesoderm of the blastula

what are BMPs

1) the ectoderm to become epidermis

2) mesoderm to become ventral mesoderm

what do BMPs induce

DBL release chordin and noggin which bind to BMPs and inhibit them lading to a gradient of BMPs → high concentration of BMPs on ventral side and low on dorsal side

what does the DBL release and what does it lead to

ectoderm → nervous system

mesoderm → dorsal mesoderm

when BMPs are inhibited what does ectoderm and mesoderm become

double gradient hypothesis

1) Wnt is a morphogen that is present in high levels in the posterior and low levels in the anterior (inhibitors present in the anterior region)

2) Retonic acid is another morphogen that is high in posterior and low in anterior

how does the anterior-posterior axis form

nodal (morphogen) activated Ptix2 gene in a gradient resulting in asymmetrical development

how does left-right axis form

mutation in the Ptix2 gene causing the heart to not be as far left as it should be

what happens in Rieger’s syndrome