In order to achieve the main objectives of elucidating the molecular mechanisms regulating inhibitory cell survival in the developing cortex, the project is divided into several work projects as described below, together with its main objectives and key findings.
Work Package 1
The main objective for this work package is to characterise neuronal cell death in the developing mouse cortex. To achieve this, we have performed stereology, an unbiased and systematic method of estimating the number of cells in a tissue. By using this method, we were able to determine changes in the number of pyramidal cells and the main subtype of interneurons, namely the medial ganglion eminence (MGE) interneurons at different time points during the first three weeks of postnatal development.
The key findings are as follows:
(1) Pyramidal cells undergo programmed cell death during the first week of postnatal development where around 13% of excitatory cells die by postnatal (P) day 5.
(2) MGE interneurons undergo programmed cell death between P5 and P10, where around 30% of MGE interneurons die.
Together, this data suggest that there is a consecutive wave of programmed cell death in early postnatal cortex and that this two events may be linked during development.
Work Package 2
The main objective for this work project is to determine the molecular mechanisms underlying interneuron cell death. To achieve this, we have divided this work package into the following subproject as listed below
(a) Impact of pyramidal cell activity and number on interneuron survival
(b) Identification of the molecular mechanisms driving MGE interneuron cell death
(c) Identification of the molecular mechanisms driving caudal ganglionic eminence (CGE), the other interneuron subtype cell death
The key findings are as follows
(1) Alteration of pyramidal cell activity or numbers can impact both MGE and CGE interneurons survival during a critical time window in development. For instance, increasing pyramidal cell activity or number enhanced the survival of interneurons during this critical time period in development. Alteration of pyramidal cell activity beyond this critical time window has no impact on interneuron survival.
(2) PTEN, a known inhibitor of PI3 kinase (a molecule that has been associated with cell survival), is expressed at different levels during the first two weeks of postnatal development. A peak expression of PTEN was observed at P7-P8 within the MGE interneuron population, corresponding to the peak of their cell death.
(3) Pyramidal cell can regulate the survival of inhibitory cell via an activity-dependent modulation of interneuron PTEN levels.
Together, our findings have demonstrated that early postnatal activity-dependent mechanisms dynamically adjusted inhibitory cell numbers and ultimately led to the establishment of the appropriate excitatory to inhibitory balance during early postnatal development. Current work is still ongoing on the molecular mechanisms regulating CGE interneuron cell death.
This work has resulted in a high-impact publication (Wong et al. Nature 2018) and has been disseminated in both national and international conferences. Furthermore, to increase the exposure of the work to the general public, a layman summary of this work has been written in international newspapers such as the Financial Times (
https://preview.tinyurl.com/yy654p6m(öffnet in neuem Fenster)) science blogs (
https://www.nature.com/articles/s41586-018-0139-6/metrics(öffnet in neuem Fenster)) and podcast (
https://tinyurl.com/y2tfn9bc(öffnet in neuem Fenster)).
