Left-right asymmetry in chicken embryonic gonads

Abstract

Avian embryos have reproductive organs with unique characteristics. In female, the gonads develop asymmetrically: the left gonad generates a functional ovary, whereas the right gonad and associated embryonic oviduct (Müllerian duct) regress. In males, however, both left and right gonads develop into testes. Recent evidence, however, revealed that left-right asymmetry can be detected in both sexes. Even male embryos have a greater number of germ cells in the left gonad. Moreover, pluripotency-associated markers, as well as SSEA1, the surface antigen that is strongly expressed in chick embryonic stem cells, also show asymmetric expression in both sexes both in germ cells and in stromal cells of the gonad. This review provides an update of the state of the field.