BMP signaling can be fine-tuned through phosphorylation of Smad1/5/8 linker regions. Smad1 linker phosphorylation integrates diverse signals to control BMP signaling through interplay between phosphorylation, ubiquitination, and exclusion from the nucleus. The level of BMP activity in developing tissues is also fine-tuned by secreted proteins that modulate BMP interaction with receptors and proteases that regulate BMP trap proteins. The 1942 Spemann Organizer graft experiment demonstrated that transplanting the dorsal lip of a salamander embryo induced neighboring cells to adopt more dorsal fates, organizing nervous system, somite and kidney tissues and establishing patterning of the embryo.

1. BMP signaling can be fine-tuned at the level of Smad1/5/8 linker phosphorylation. Discuss
Briefly describe the Spemann Organizer graft experiment and outcomes.
Solution
A). Bone morphogenetic protein (BMP) are a group of signalling molecules that belongs to the
transforming growth factors.These proteins are important in embryogenesis& development,also
in maintenance of adult tissue homeostasis.BMP signalling pathway components resulting in
embryonic lethality or marked defects is shown by "MOUSE KNOCKOUT" model.BMPs
signal via canonical pathways or non- canonical pathway(Smad- dependent pathway).In
canonical pathway, BMPs are initiated by signal transduction cascade binding to typeI or typeII
serine/threonine kinase receptors and thus form heterotetrameric complex.Consitutively,active
type II receptor transphosphorylates the type I receptor & then typeI receptor phosphorylates the
receptor-regulated Smads (R-Smads 1//5/8).R-Smads associates with smad4 and further
associates with coactivators or core pressers to regulate gene expression.Smad1 linker
phosphorylation acts as interdependent inputs to control BMP signalling.The interplay between
linker phosphorylation,ubiquitination& nucleoporin exclusion enables regulation of BMP action
by diverse signals.Secreted proteins that trap BMPs to modulate their interaction with membrane
receptors & specific protease a that control the activity of these BMP traps establish a fine-tuning
of BMP activity in developing tissues.
B) Spemann Organizer Graft Experiment with outcomes-
Experiment was performed in 1942. Mangold with Spemann used salamander eggs of species
that differed in their pigmentation.They demonstrated that the graft became notochord yet
induced neighbouring cells to change fates because the fate of transplanted cells could be traced
during development.The neighbouring cella adopted differentiation pathways that were more
dorsal & produced tissues such as central nervous system,somites& kidneys.The transplanted
cells organize a perfect dorsal-ventral & anterior-posterior pattern in induced tissues.Their
experiment established the key importance of cell -cell inductions during animal development.