Two distinct populations of neoblasts exist:

1. Sigma neoblast population 

2. Zeta neoblast population 

TLS Online TPP Program

#Id: 1377

#Unit 4. Cell Communication and Cell Signaling

Short-term regulation: 

JAK2 deactivation by SHP1 phosphatase

TLS Online TPP Program

#Id: 1378

#Unit 4. Cell Communication and Cell Signaling

Long-term regulation: 

• SOCS proteins

• Targets the receptor as well as JAK2 for degradation by the ubiquitin-proteasome pathway

TLS Online TPP Program

#Id: 1379

#Unit 4. Cell Communication and Cell Signaling

The rate-limiting step in actin filament assembly is the formation of a short actin oligomer (nucleus).

TLS Online TPP Program

#Id: 1380

#Unit 4. Cell Communication and Cell Signaling

The critical concentration (Cc) is the concentration of free G-actin at which the filaments are formed.

TLS Online TPP Program

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#Unit 4. Cell Communication and Cell Signaling

At steady state, ATP–G-actin subunits add preferentially to the (+) end, while ADP–G-actin subunits disassemble from the (−) end, giving rise to treadmilling of subunits.

TLS Online TPP Program

#Id: 1382

#Unit 4. Cell Communication and Cell Signaling

Profilin enhances the exchange of ADP for ATP on G-actin. Cofilin enhances the rate of loss of ADP-actin from the filament (−) end. Thymosin-β4, binds to ATP–G-actin in such a way that it inhibits addition of the actin subunit to either end of the filament.