The major questions…

• Further refine the timing of Golgi fission in G2

• Elucidate the role of BARS in Golgi fission

• Elucidate the Golgi mitotic checkpoint model

Background

Image from http://www.molecularexpressions.com/cells/golgi/golgiapparatus.html

Authors’ Conclusions

• Identifies an earlier stage of Golgi partitioning, namely severing of the non-compact zones in G2 to make isolated stacks

• Identifies the role of BARS in the Golgi mitotic checkpoint

• Sets the stage for continued molecular dissection of the Golgi mitotic checkpoint pathway

The Golgi begins to dissolve in G2

EM based examination of Golgi fission in interphase vs. G2

What is FRAP?

GalT-GFP

1. Source of Fluorescence2. Bleach with a laser3. Wait (minutes)4. Graph recovery

recovery (intact) no recovery (not intact)

Is BARS required for fission during G2?

Cells with isolated stacks are resistant to BARS inhibition

Golgi morphology in MEFs lacking BARS

Authors’ Conclusions

• Identifies an earlier stage of Golgi partitioning, namely severing of the non-compact zones in G2 to make isolated stacks

• Identifies the role of BARS in the Golgi mitotic checkpoint

• Sets the stage for continued molecular dissection of the Golgi mitotic checkpoint pathway

Implications of this study

• Is there a Golgi mitotic checkpoint?– Part of the G2/M checkpoint? Is BARS inhibited

upon DNA damage?– Could Golgi disassembly simply be a requirement

for centrosome activation and separation?

• Why do you need the haze?– Shouldn’t BARS-dependent fragmentation be

sufficient for Golgi segregation to daughter cells?

Future Studies

• How is BARS regulated? – PAK1– MEK1– Others– DNA damage checkpoint???

• Does BARS get degraded at M entry?• What proteins does BARS associate with? • What are the substrates of BARS?