(C) Single cells were grouped into 60 clusters according to their expression of genes encoding homeodomain proteins (Fig 2A) and arranged along the inferred AP position (Fig 1D, 1E). For each cluster, the mean expression of Ig encoding genes was computed. Heatmap depicts Ig encoding genes in columns and clusters in rows; mean expression is color-coded and median expression level is visualized by circle size. Gene families are highlighted in color codes. The colored bars highlight the Ig genes expressed in anterior MNs (MN2c, MN2a, MN4, MN3). 