The amygdala is an almond shaped structure located in the temporal lobe and thought to be essential for decoding emotions and in particular stimuli that are threatening to the animal. It is composed of a large number of structures and constitutes the amygdaloid complex (AC). Despite its importance, however, developmental origins of amygdalar neurons and glial cells remain poorly understood due largely to its complicated structure. Recent studies including genetic fate mapping studies have shown that the lateral ganglionic eminence is an important source of amygdalar neurons. However, progenitor origins of amygdalar cell groups remain partially understood. In addition, almost nothing is known about the developmental origin of glial cells.
In this study we applied in utero electroporation to uncover developmental origins of the cell groups that constitute the AC. To permanently label progenies of electroporated progenitors, we electroporated pCAGGS-mCherry to embryonic day 10.5 mice together with a mixture of pT2K-CAGGS-EGFP, which is a Tol2 transposon-flanked EGFP, and pCAGGS-T2TP that codes for Tol2 transposase (Yoshida et al., Genes to Cells, 5:501) directing electrodes toward the ganglionic eminences. Labelled cells were observed at postnatal day 21 and later.
We found that cells in the AC are labelled in most cases, but the labelled structures in the AC varied between animals. However, the results can be categorized into four types based on labelled structures within the AC: 1) Cells in the basolateral group are mainly labelled; 2) Those in the centromedial and cortical part are mainly lablled; 3) Both of these groups are labelled; 4) Cells in the intercalated masses are labelled. These findings indicate that the cells of the AC originate from three distinct progenitor domains. Interestingly, while pCAGGS-mCherry exclusively labeled neuronal cells, pT2K-CAGGS-EGFP labelled both neuronal and glial cells. Thus, both neuronal and glial cells that comprise the AC likely originate from common progenitors but are generated at different developmental time windows.