Keywords: v. cell biology of disease; i. receptor tyrosine kinase/phosphatase
Activating mutations of both PLC-γ1 and -γ2 are observed in a variety of human diseases. This includes somatic mutations in a variety of cancers, as well as germline changes underlying auto-immune disorders; some inherited, activating, PLC-γ mutations have also been shown to be protective in early-onset Alzheimer disease. Drosophila has a single PLC-γ homolog encoded by small wing (sl) and although many sl mutations have been isolated, all are either hypomorphic or loss of function alleles. We are therefore using CRISPR to recreate in Drosophila some of the most commonly observed mammalian PLC-γ activating mutations. These mutant lines should be useful both in understanding the role of increased PLC-γ signaling in human disease, as well as providing reagents to screen for drugs that block this activation. One successful edit made to date is viable, mimicking the PLCγ1 S345F mutation observed in the malignancies from many human T cell leukemia patients. Flies homozygous for an slS349F edited X-chromosome typically show normal eye development but, in a background with increased dosage of sl+, ommatidia in two independent lines frequently show abnormal photoreceptor development, in which R3 is replaced by two photoreceptor cells with smaller rhabdomeres. This phenotype is similar to that seen in loss of function mutations of the nuclear receptor encoded by seven-up, in which R1, R3, R4, or R6 cells are transformed into R7. We are in the process of isolating additional activating mutations, and further characterizing the defect in the slS349Fmutant line.