Fig. 3. dILA neurons are the product of asymmetric cell divisions. (A) Summary of all possible cell divisions that could generate dILA or dILB neurons. Yes/no indicates if a particular type of progenitor cell division was observed by lineage tracing experiments using retroviral infection. (B) Quantification of the different types of independent two-cell clones observed after retroviral infection. (C-G) Two-cell clones residing in the dorsal spinal cord were identified after retroviral infection by the expression of ß-galactosidase, as assessed by immunohistochemisty (green). The molecular identity of cells was assessed by the use of antibodies directed against Lbx1 (red) and Lhx1/5 (blue). dILA neurons were defined as Lbx1+/Lhx1/5+ cells, dILB neurons as Lbx1+/Lhx1/5– cells, and progenitors as Lbx1-negative cells located close to the ventricle. Only those clones that contained at least one Lbx1+ neuron were assessed. Spinal cords are shown at low (C) and high (D-G) magnification. (E) High magnification of a two-cell clone containing one dILA (white) and one dILB (yellow) neuron. (G) High magnification of a two-cell clone containing two dILB neurons (yellow). Scale bar: 100 µm in A;10 µm in B-E.