Functional dissection of Timekeeper (Tik) implicates opposite roles for CK2 and PP2A during Drosophila neurogenesis

Area of Science:

• Developmental Biology
• Cell Signaling
• Molecular Genetics

Background:

• Notch (N) signaling is crucial for lateral inhibition, a process regulating cell fate during development.
• Protein kinase CK2 is known to regulate E(spl)M8 repression during inhibitory N signaling.
• The role of phosphatases in this process has remained largely uncharacterized.

Purpose of the Study:

• To investigate the involvement of a phosphatase in the regulation of E(spl)M8 repression during N signaling.
• To elucidate the functional relationship between protein kinase CK2 and phosphatases in N signaling.

Main Methods:

• Utilized a dominant-negative (DN) mutation (Tik) in the catalytic subunit of CK2 within a Gal4-UAS based assay.
• Examined phenotypes in Drosophila melanogaster, including ectopic bristles and retinal defects, using gain-of-function alleles of N.
• Performed functional dissection of mutations within Tik and overexpressed microtubule star (mts), the PP2A catalytic subunit.

Main Results:

• Overexpression of Tik induced ectopic bristles in N(+) flies and suppressed retinal defects in N(spl) flies.
• Mutations in Tik impairing ATP-binding and PP2A binding contributed to its dominant-negative effects.
• Overexpression of mts mimicked the loss of CK2 function phenotypes and induced notched wings, characteristic of N mutations.

Conclusions:

• Protein kinase CK2 and phosphatase PP2A play antagonistic roles in inhibitory Notch signaling.
• The findings provide new insights into the molecular mechanisms regulating lateral inhibition and cell fate determination.