Shox2 is essential for maintenance of physiological properties and functions of thalamic neurons in young adult mouse
The lack of Short Stature Homeobox Gene, SHOX, caused several symptoms in humans including the short stature, skeletal abnormalities, heart diseases and cognitive problems. To understand the role of SHOX and SHOX2 in humans, the study of homolog gene Shox2 in mice has been applied. Previous researches have revealed that Shox2 has important role in bone, palate, heart and hindbrain development. Especially, Shox2 is critical for the development of heart pacemaker cells. In this dissertation, we studied the role of Shox2 in the thalamus of young adult mice. Our results indicated that Shox2 expression during development in the forebrain is relatively limited in the thalamus. To study the role of Shox2 in thalamic properties and functions, we conducted tamoxifen inducible knock out (KO) in RosaCreERt/+, Shox2f/f mice. Our behavioral studied showed that Shox2 KO impairs mice total activity, somatosensory function and learning and memory process, suggesting Shox2 is critical for thalamus-related behaviors. To investigate the underlying mechanism, we conducted electrophysiological experiment to test physiological properties of thalamic neurons. Our results showed that Shox2 KO caused changes in intrinsic properties including decreased cell excitability. Besides, our TUNEL staining results revealed Shox2 inducible KO in midline thalamus οf Gbx2CreERt/+, Shox2f/f mice caused increased cell death in the midline thalamus. We further investigate whether pacemaking related ion channels are involved in cellular properties impairments caused by Shox2 KO. The following experiments revealed a decrease in mRNA and protein expression of Cav3.1 and T-type calcium current density, and in mRNA and protein expression of HCN2 and HCN4 channels and HCN current. The similar enriched genes related to T-type calcium and HCN channels with heart pacemaker cells and the specific down-regulation of these genes by Shox2 KO suggested the critical role of Shox2 in maintenance of thalamic pacemaking properties and behavioral functions. Our mRNA sequencing results indicated that enriched differently expressed genes (DEGs) in gene ontology (GO) terms of cell death, neuron projection development and response to stimulus between CR and KO samples and thalamus specifically enriched genes are highly regulated by Shox2 KO, suggesting Shox2 is important for thalamic identity and survival.