Histogenetic pleiotropism in the crooked neck dwarf chick embryo: degeneration of the trachea and thymus.

TLDR: Retrogressive analysis of the cn gene effect has been performed on crooked neck dwarf chick embryos between stages 28–38, providing some explanation for “escapers,” homozygous lethal embryos known to survive until hatching.

Abstract: Retrogressive analysis of the cn gene effect has been performed on crooked neck dwarf chick embryos between stages 28–38 (5–12 days). The phenocritical stage of mutant embryos studied is stage 29. Histolytic degeneration of neck tissues is first recognized by the appearance of localized degenerate nuclei in the tracheal mesenchyme. Pleiotropic autolysis of the embryonic thymus, loose mesenchyme and the ventral neck tissue is also observed. Histolysis occurs in a caudocephalic gradient in all cn-affected embryos. The degenerative effects in crooked neck dwarf embryos vary in their intensity, but the pattern of autolysis seems constant. Histological observations provide some explanation for “escapers,” homozygous lethal embryos known to survive until hatching. A mechanism for surviving developmental crises in cn embryos is proposed.