Table 1.
Maturation age of the paraxial mesoderm expressing a gene at selected stages of development
| Stage | HH4/5 | HH8 | HH10 | HH14 | HH16 | HH19/20 | Comments |
|---|---|---|---|---|---|---|---|
| Key feature | Fully extended primitive streak – streak beginning to retract, head process visible | 4 somites | 10 somites | 22 somites | 26–28 somites | 37–43 somites | |
| Gene | |||||||
| Tbx6; expression encompasses | n = 2; ps/ emerging mesoderm | n = 3; ps, sp, s0 | n = 5; ps, sp, s0–s2/3 | n = 5; tb, sp, s0 | n = 5; tb, sp, s0–s1 | n = 3; tb–s1/2 | |
| Onset | |||||||
| Paraxis | n = 3; condensing somite | n = 2; rostral sp, s0 | n = 10; rostral sp, s0 | n = 3; rostral sp, s0 | n = 4; rostral sp, s0 | n = 10; sp–s0 | |
| Pax3 | n = 4; ps, epiblast | n = 4; s0 | n = 2; s0 | n = 5; s0 | n = 5; rostral sp, s0 | n = 10; sp–s0 | Prominent expression in the neural tube and in neural crest cells |
| Pax7 | n = 4; ps | n = 4; s0 | n = 5; s0 | n = 4; s0 | n = 4; rostral sp, s0 | n = 9; sp–s0 | Prominent expression in the neural tube and in neural crest cells |
| Six1 | n = 2; head mesoderm | n = 2; s0 | n = 7; s0 | n = 2; s0 | n = 5; rostral sp, s0 | n = 10; rostral sp, s0 | Expression in the HH5-10 head mesoderm |
| Eya1 | n = 2; ps | n = 1; s0 | n = 3; s0 | n = 2; s0 | n = 1; rostral sp, s0 | n = 6; sp, s0 | |
| Myf5 | n = 3; – | n = 4; – | n = 7; s0–s1 | n = 7; s0–s1 | n = 8; s0–s1 | n = 11; s0–1 | |
| MyoD | n = 3; – | n = 3; – | n = 4; – | n = 8; s4/5 | n = 6; s1/2 | n = 7; s1/2 | |
| MyoG | n = 1; – | n = 1; – | n = 1; – | n = 4; s9/10 | n = 4; s6/7 | n = 4; s5 | |
| Mrf4 | n = 2; – | n = 3; – | n = 2; – | n = 9; s9/10 | n = 7; s8/9 | n = 7; s6–8 | Low overall expression levels |
| Mef2a | n = 5; ps | n = 2; – | n = 1; – | n = 7; s1 | n = 8; s1; myotome s10 | n = 1; s1 | Low overall expression levels; HH7-16: widespread expression, strongest: cardiac precursors; HH16 onwards: upregulated in the mature myotome |
| Mef2c | n = 1; – | n = 8; weak signal in somites | n = 8; weak signal in s1–3 | n = 5; s5–7 | n = 4; s3/4 | n = 3; s3 | HH7-14: strongest signal in cardiac precursors |
| Mef2d | n = 1; – | n = 1; – | n = 1; – | n = 2; s6–8 | n = 2; s7–9 | n = 2; s4/5 | Low overall expression levels, strongest: cardiac precursors |
| Mef2b | n = 1; – | n = 1; s1 | n = 1; s1 | n = 3; s1 | n = 1; s1 | n = 1; s1 | HH7-14: widespread expression, strongest in ps and somites |
| Cdh4 | n = 1; – | n = 2; – | n = 5; – | n = 6; s7–9 | n = 2; s0,s1; then from s7/8 onwards | n = 10; s3/4 | HH7-10: notochord; from HH13/14 onwards: intermediate mesoderm; low overall expression levels |
| Desmin | n = 1; – | n = 1; – | n = 1; – | n = 2; s10–12 | n = 2; S11–13 | n = 6; s7/8 | Weak signal; HH13/14 onwards: prominent expression in heart; low overall expression levels |
| Tnni1 | n = 1; – | n = 2; – | n = 1; – | n = 1; s9/10 | n = 2; s5/6 | n = 6; s4/5 | HH7-10 onwards: cardiac precursors; heart |
| Myh15 | n = 1; – | n = 2; – | n = 3; – | n = 3; s20/21 | n = 3; s14/15 | n = 2; s11/12 | HH7-10 onwards: cardiac precursors; heart |
| Myh7 | n = 1; – | n = 2; – | n = 3; – | n = 3; – | n = 3; s19/20 | n = 2; s11–13 | Low overall expression levels; HH7-10: precursors of cardiac inflow tract; HH13/14 onwards: heart |
| Sarcomeric myosins | n = 3; – | n = 1; – | n = 3; – | n = 2; s16/17 | n = 4; s14–16 | n = 4; s8–9 | HH9/10 onwards: heart |