Fig. 5: A subpopulation of muscle progenitors aggregated at the proximal region of emu forelimb buds undergoes cell death.
a Violin plots showing the expression levels of Bak1, Casp10 and Apaf1 in Pax3 + /Hand2- cells, or Pax3 + /Hand2+ cells in the muscle cluster of stage 25 emu forelimb data. b–d TUNEL staining (b, n = 3), immunostaining for active caspase-3 (c, n = 2) and immunostaining for 8-oxoguanine (d, n = 2) in the aggregated cell population at the proximal region of stage 25 emu forelimb buds. b’–d’ Enlarged images indicated in (b–d). Panels of (b, b’) and (c, c’) are flipped horizontally. Scale bars, 50 μm. e Schematic model of forelimb development in emu embryos. Migratory muscle precursors (Pax3 + , Lbx1 + , cMet + ) delaminated from the ventral edge of the dermomyotome and begin to migrate into the forelimb mesenchyme (Hand2 + , Prrx1 + , Tbx5 + ). Subsequently, a subpopulation of muscle precursors with a dual somite-derived myogenic cell (Pax3 + , Lbx1 + , cMet + ) /LPM cell (Hand2 + , Prrx1 + , Tbx5 + ) appears and aggregates at the proximal part of forelimb buds. This aggregated cell population undergoes cell death and thereby failing to form majority of muscles. Impaired formation of limb muscles seems to be at least partially responsible for the asymmetric reduction or fusion of distal skeletal elements. Our results and those of others2,5,6,7,8,9 suggest that multiple mechanisms contribute to the unique emu wing morphology. See text for details.
