The zona pellucida in mammals plays a role analogous to that of the vitelline envelope in invertebrates; the zona, however, is a far thicker and denser structure than the vitelline envelope

TLS Online TPP Program

#Id: 9353

#Unit 4. Cell Communication and Cell Signaling

The function of RIII for TGF-β receptors is similar to that of the α subunit of the IL-2 receptor 

(means facilitating TGF-β binding to the RII and RI)

   

         

TLS Online TPP Program

#Id: 9355

#Unit 4. Cell Communication and Cell Signaling

Most cells lack RIII, TGF-β binds directly to the RII

dimer, but Active RII kinase activity is not sufficient to generate an intracellular signal

TLS Online TPP Program

#Id: 9356

#Unit 4. Cell Communication and Cell Signaling

RI will not bind to RII unless RII is bound to TGF-β.

TLS Online TPP Program

#Id: 9357

#Unit 4. Cell Communication and Cell Signaling

RII phosphorylates serine and threonine in the juxtamembrane segment of the RI (ligand induced receptor hetero-oligomerization), releasing the inhibition of RI kinase activity.

TLS Online TPP Program

#Id: 9358

#Unit 4. Cell Communication and Cell Signaling

Active type I receptor kinase phosphorylates a Smad

TLS Online TPP Program

#Id: 9359

#Unit 4. Cell Communication and Cell Signaling

Three types of Smad proteins function in the TGF-β signaling pathway: 

R-Smads (Smad2 and Smad3)

Co-Smads (Smad4)

I-Smads (Smad7)