Developmental characterization of <i>Zswim5</i> expression in the progenitor domains and tangential migration pathways of cortical interneurons in the mouse forebrain

<jats:title>Abstract</jats:title> <jats:p> GABAergic interneurons play an essential role in modulating cortical networks. The progenitor domains of cortical interneurons are localized in developing ventral forebrain, including the medial ganglionic eminence (MGE), caudal ganglionic eminence (CGE), preoptic area (POA), and preoptic hypothalamic border domain (POH). Here, we characterized the expression pattern of <jats:italic>Zswim5</jats:italic> , an MGE‐enriched gene in the mouse forebrain. At E11.5–E13.5, prominent <jats:italic>Zswim5</jats:italic> expression was detected in the subventricular zone (SVZ) of MGE, POA, and POH, but not CGE of ventral telencephalon where progenitors of cortical interneurons resided. At E15.5 and E17.5, <jats:italic>Zswim5</jats:italic> expression remained in the MGE/pallidum primordium and ventral germinal zone. <jats:italic>Zswim5</jats:italic> mRNA was markedly decreased after birth and was absent in the adult forebrain. Interestingly, the <jats:italic>Zswim5</jats:italic> expression pattern resembled the tangential migration pathways of cortical interneurons. <jats:italic>Zswim5</jats:italic> ‐positive cells in the MGE appeared to migrate from the MGE through the SVZ of LGE to overlying neocortex. Indeed, <jats:italic>Zswim5</jats:italic> was co‐localized with <jats:italic>Nkx2.1</jats:italic> and Lhx6, markers of progenitors and migratory cortical interneurons. Double labeling showed that Ascl1/Mash1‐positive cells co‐expressed <jats:italic>Zswim5</jats:italic> . <jats:italic>Zswim5</jats:italic> expressing cells contained none or at most low levels of Ki67 but co‐expressed Tuj1 in the SVZ of MGE. These results suggest that <jats:italic>Zswim5</jats:italic> is immediately upregulated as progenitors exiting cell cycle become postmitotic. Given that recent studies have elucidated that the cell fate of cortical interneurons is determined shortly after becoming postmitotic, the timing of <jats:italic>Zswim5</jats:italic> expression in early postmitotic interneurons suggests a potential role of <jats:italic>Zswim5</jats:italic> in regulation of neurogenesis and tangential migration of cortical interneurons. </jats:p>