Spatial transcriptomic analysis of mouse parathyroid gland cells expressing an activating variant of <i>Gcm2</i>

Glial cells missing 2 (<i>GCM2</i>) is an essential transcription factor for the development of parathyroid glands. Germline <i>GCM2</i> variants that repress or enhance transcriptional activity predispose a subset of patients to hypoparathyroidism or hyperparathyroidism, respectively. A recurrent germline heterozygous activating missense variant of <i>GCM2</i>, p.Y394S has been identified in some patients with primary hyperparathyroidism. A genetically engineered knock-in mouse model of this variant corresponding to p.Y392S in the mouse <i>Gcm2</i> gene (<i>Gcm2</i> ^+/Y392S) did not show obvious parathyroid tumors. However, in GCM2-binding site mediated luciferase reporter assays in HEK293 cells, the mouse and the human variant both exhibited enhanced transcriptional activity. Therefore, we assessed the effect of this variant on gene expression in vivo in parathyroid glands from <i>Gcm2</i> ^+/Y392S and WT mice. Using the 10x Genomics Visium platform, spatially resolved transcriptomic analysis was performed on formalin-fixed and paraffin-embedded (FFPE) tracheal tissue sections of <i>Gcm2</i> ^+/Y392S and WT mice to capture RNA from parathyroid glands together with other cell types in the tissue sections. Transcriptome sequence data analysis detected 8 different clusters in the tissue sections based on similarity of gene expression profiles. Cluster-1, which contained parathyroid gland cells expressing <i>Pth</i> and <i>Gcm2</i>, was further evaluated for transcripts that were differentially expressed more than 2-fold in <i>Gcm2</i> ^+/Y392S compared to WT. Increased transcript level of <i>Lgals3</i> (galectin-3) was seen in <i>Gcm2</i> ^+/Y392S parathyroid gland cells which is among markers of parathyroid carcinoma. Galectin-3 protein was detected in available FFPE human parathyroid samples of patients with germline heterozygous activating <i>GCM2</i> variants, p.Y394S (<i>n</i> = 4/10) or p.L379Q (<i>n</i> = 2/2). These results indicate a potential for growth and malignancy of parathyroid glands expressing <i>GCM2</i> variants. The transcriptomic data of mouse parathyroid gland cells generated in this study can serve as a valuable resource for investigating genes and pathways in normal or abnormal parathyroid gland growth and physiology.