MST1 and MST2 are expressed during development in various brain regions.

Neuron specific deletion of hippo (Mammalian Ste20-like kinase MST1/2 in mammals) or wts (Large Tumour Suppressor kinase Lats1/2 in mammals) in drosophila sensory neurons leads to deficiencies in maintenance of neuronal dendritic arbors, while deletion of hippo or another NDR kinase trc (Nuclear Dbf2 Related kinase, NDR1/2 in mammals) causes increased dendrite branching in flies, implicating MST1/2 signaling in dendritic development.

Although roles of the tumour suppressor Hippo/ MST1/2 in cell division, apoptosis, cell polarity and tissue size control have been studies in detail, whether or not MST1/2 functions in mammalian neuronal development is an open question. We plan to address this question using MST1/2 neuronal conditional knockout mice.

MST1 and MST2 are expressed during development in various brain regions. In situ hybridisation revealed that MST1 is localised to hippocampal pyramidal cell layers and dentate granule cells. In order to test if MST1/2 function is required in neuronal development, we have crossed Mst1/2 floxed (Mst1 f/f; Mst2 f/f) mice with Nex-Cre mice, which express Cre recombinase in excitatory neurons of hippocampus and cortex.

As expected, MST1 and MST2 protein levels are reduced in the knockout hippocampi. In these neuronal conditional MST1/2 knockout mice we are investigating if MST1/2 is required for synapse development by performing whole-cell patch clamp electrophysiological recordings.

We are also characterising dendrite arbors and dendritic spine morphologies using either fluorescently-recovered biocytin fills obtained during recordings or by using Thy1YFP mice and confocal imaging.

We are then going to characterise if MST1/2 acts via its canonical effector Lats1/2 or a related kinase NDR1/2. In parallel, we aim to identify novel MST1/2 kinase substrates by using chemical genetics.