Functional analyses of mouse ASK, an activation subunit for Cdc7 kinase, using conditional ASK knockout ES cells

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Cdc7 kinase is essential for cell cycle progression.
• ASK is an essential activation subunit for mammalian Cdc7 kinase.
• Understanding ASK's function is critical for cell viability.

Purpose of the Study:

• To investigate the essential roles of ASK in mouse embryonic stem (ES) cell viability.
• To functionally dissect the ASK protein using conditional inactivation in ES cells.
• To identify critical motifs within ASK required for its in vivo function.

Main Methods:

• Generation of conditional ASK-deficient ES cell lines.
• Analysis of cell growth, DNA synthesis, and cell death upon ASK inactivation.
• Functional characterization of ASK motifs (M, C, N, and C-terminal tail).
• Assessment of MCM phosphorylation and Cdc7 autophosphorylation activity.

Main Results:

• ASK deficiency leads to rapid cessation of ES cell growth, DNA synthesis arrest, and cell death.
• Conserved motifs M and C are essential for ASK function, while the C-terminal tail is dispensable.
• Motif-N, dispensable in yeast, is essential for ES cell viability.
• Motif-N is required for maximal MCM phosphorylation, but not Cdc7 autophosphorylation.

Conclusions:

• ASK is essential for the viability of mouse ES cells.
• Motif-N of ASK plays a critical role in ES cell survival, likely by facilitating substrate recruitment for Cdc7 kinase.
• These findings highlight species-specific differences in ASK function and provide insights into cell cycle regulation.