It not only expresses the typical ORS marker KRT14 but is also enriched for companion layer marker KRT75 plus KRT6C and mouse bulge SC marker SOX9 plus LHX2. Its closest counterpart in mouse HF would be the “Inner Bulge” cells that are ORS derivatives enriched for K6 and SOX9 expression33. Here, KRT75 is linked to hydrops fetalis.