Table 1. Details of individual experiments performed in the four different laboratories (University College London, UCL, University of Glasgow, UoG, Max Delbrück Center for Molecular Medicine, MDC, Salk Institute), with individual cell count and virus concentration.

Same experimental code as in Figures 3D-E—6B, E, H, Figures 8E and 9E and Figure 11E and figure supplements. Experiments performed at the Salk Institute (except the PRV-Bartha experiments) were co-injections of either AAV6-B19G (3×10¹² titre) or of AAV6 - CAG-Flex-optimizedG (oG, 1×10¹² titre). AAV and RV were injected in a 3:1 ratio. For all labs and muscles the total volume injected was 1 μl, with the exception of PRV-Bartha experiments, where 0.5 μl were injected. In the Salk Institute experiments, no attempt was made to identify primarily infected motor neurons, therefore the cell count refers to both motor neurons and interneurons.

Code	Lab	Injection	Perfusion	Muscle	TitreI.U.	MNs	Double labelled MNs	Ipsi dorsal median (μm)	Ipsipremotor INs	Contrapremotor INs	Totalpremotor INs	premotor INs/MNs ratio	Section sampling
170427 n2	UCL	P2	P11	LG	1×1010	46	3	285	741	116	857	19	1/2 (30 μm)
				TA	5×109	41		298	912	88	1000	24
170427 n3	UCL	P2	P11	LG	1×1010	32	2	267	620	87	707	22	1/2 (30 μm)
				TA	5×109	6		276	386	34	420	70
170503 n6	UCL	P2	P11	LG	1×1010	83	1	294	1935	639	2574	31	1/2 (30 μm)
				TA	5×109	55		315	1887	315	2202	40
170125 n3	UCL	P1	P10	LG	5×109	39	0	365	670	107	777	20	1/2 (30 μm)
				MG	5×109	39		353	819	307	1126	29
170508 n7	UCL	P2	P11	LG	1×1010	110	3	352	1955	382	2337	21	1/2 (30 μm)
				MG	5×109	67		322	1497	429	1926	29
170125 n7	UCL	P1	P10	TA	5×109	47	0	363	907	308	1215	26	1/2 (30 μm)
				PL	5×109	39		380	1044	195	1239	32
170125 n8	UCL	P1	P10	TA	5×109	22	2	343	920	157	1077	49	1/2 (30 μm)
				PL	5×109	22		330	741	83	824	37
1570	UoG	P1	P10	LG	2×108	11	-	322	1111	404	1515	138	1/8 (60 μm)
1571	UoG	P1	P10	LG	2×108	12	-	340	760	196	956	80	1/8 (60 μm)
1573	UoG	P1	P10	TA	5×108	10	-	332	447	68	515	52	1/8 (60 μm)
1574	UoG	P1	P10	TA	5×108	14	-	365	297	26	323	23	1/8 (60 μm)
1577	UoG	P2	P10	LG	2×109	18	2	329	313	43	356	20	1/8 (60 μm)
				TA	5×109	26		312	688	105	793	31
1578	UoG	P2	P10	LG	2×109	21	5	330	292	34	326	16	1/8 (60 μm)
				TA	5×109	22		346	790	130	920	42
1579	UoG	P2	P10	LG	2×109	30	1	322	1023	194	1217	41	1/8 (60 μm)
				MG	5×108	7		306	169	19	188	27
1580	UoG	P2	P10	LG	2×109	14	0	316	414	48	462	33	1/8 (60 μm)
				MG	5×108	8		348	470	87	557	70
1605	UoG	P1	P10	MG	1×108	6	-	340	412	110	522	87	1/8 (60 μm)
1611	UoG	P1	P10	PL	1×108	2	-	328	167	24	191	96	1/8 (60 μm)
1613	UoG	P2	P10	PL	1×108	1	-	340	164	16	180	180	1/8 (60 μm)
1639	UoG	P2	P10	TA	2×108	15	-	341	591	94	685	46	1/8 (60 μm)
1640	UoG	P2	P10	PL	2×108	20	-	322	629	122	751	38	1/8 (60 μm)
1644	UoG	P2	P10	LG	1×108	1	-	344	142	32	174	174	1/8 (60 μm)
				TA	2×108	-		296	57	11	68	-
1646	UoG	P2	P10	LG	1×108	1	-	261	90	16	106	106	1/8 (60 μm)
				TA	2×108	3		305	76	13	89	30
1653	UoG	P2	P10	LG	1×108	2	-	307	60	6	66	33	1/8 (60 μm)
				TA	2×108	2		312	58	8	66	33
1656	UoG	P2	P10	LG	1×108	-	-	311	563	145	708	-	1/8 (60 μm)
1657	UoG	P2	P10	LG	1×108	1	-	321	323	51	374	374	1/8 (60 μm)
1660	UoG	P2	P10	MG	2×108	7	-	324	509	3	512	73	1/8 (60 μm)
1661	UoG	P2	P10	MG	2×108	10	-	338	175	63	238	24	1/8 (60 μm)
1662	UoG	P2	P10	MG	2×108	10	-	313	375	230	605	61	1/8 (60 μm)
1701	UoG	P2	P10	LG	2×109	8	2	351	169	26	195	24	1/8 (60 μm)
				MG	5×109	34		329	594	190	784	23
1702	UoG	P2	P10	LG	2×109	14	2	331	561	107	668	48	1/8 (60 μm)
				MG	5×109	2		322	76	11	87	44
353	MDC	P4	P10	GS	1×109	31	-	283	1542	431	1973	64	All (40 μm)
399	MDC	P4	P10	GS	1×109	41	-	286	569	77	646	16	All (40 μm)
1332	MDC	P4	P10	GS	1×109	18	-	317	1605	323	1928	107	All (40 μm)
1349	MDC	P4	P10	GS	1×109	18	-	305	1416	459	1875	104	All (40 μm)
700	MDC	P4	P10	TA	1×109	47	-	318	1723	122	1845	39	All (40 μm)
721	MDC	P4	P10	TA	1×109	22	-	310	1934	465	2399	109	All (40 μm)
1324	MDC	P4	P10	TA	1×109	17	-	292	2041	301	2342	138	All (40 μm)
1	Salk	P2	P10	GS	1×1011	N/A	N/A	328	9185	2735	11920	N/A	All (60 μm)
				TA	1×1011	N/A	N/A	349	3330	731	4061	N/A
2	Salk	P2	P10	GS	1×1011	N/A	N/A	303	8827	3867	12694	N/A	All (60 μm)
				TA	1×1011	N/A	N/A	294	3198	1132	4330	N/A
a	Salk	P1	P8	GS	1×1010	N/A	N/A	248	334	42	376	N/A	1/9 (30 μm)
b	Salk	P1	P8	GS	1×1010	N/A	N/A	237	275	30	305	N/A	1/9 (30 μm)
22 a_4	Salk	P2	P9	GS	3×1011	N/A	N/A	403	464	58	522	N/A	All (60 μm)
26 a_1	Salk	P2	P9	GS	3×1011	N/A	N/A	383	941	91	1032	N/A	All (60 μm)
26 a_2	Salk	P2	P9	GS	3×1011	N/A	N/A	351	1910	401	2311	N/A	All (60 μm)
26 a_4	Salk	P2	P9	GS	3×1011	N/A	N/A	382	1923	392	2315	N/A	All (60 μm)
26_1	Salk	P2	P9	TA	3×1011	N/A	N/A	348	3236	263	3499	N/A	All (60 μm)
26_3	Salk	P2	P9	TA	3×1011	N/A	N/A	367	2078	465	2543	N/A	All (60 μm)
26_4	Salk	P2	P9	TA	3×1011	N/A	N/A	350	2494	597	3091	N/A	All (60 μm)
1_1 PRV	Salk	P11	P13	GS	1×109	N/A	N/A	318	430	54	484	N/A	1/4 (60 μm)
				TA	1×109	N/A	N/A					N/A
1_4 PRV	Salk	P11	P13	GS	1×109	N/A	N/A	349	238	23	261	N/A	1/4 (60 μm)
				TA	1×109	N/A	N/A					N/A
2_2 PRV	Salk	P11	P13	GS	1×109	N/A	N/A	357	515	82	597	N/A	1/4 (60 μm)
				TA	1×109	N/A	N/A					N/A
3_3 PRV	Salk	P11	P13	GS	1×109	N/A	N/A	377	1005	53	1058	N/A	1/4 (60 μm)
				TA	1×109	N/A	N/A					N/A