Differential cellular localization of galectin-1 and galectin-3 in the regressing corpus luteum of mice and their possible contribution to luteal cell elimination.

Galectin-1 and galectin-3, beta-galactoside-binding lectins, are predominantly expressed in the regressing corpus luteum (CL) of mouse ovary. This study revealed the expression patterns and cellular localizations of galectins during CL formation and regression by ISH and IHC. Galectin-1 mRNA expression temporarily increased in active CL, preceding the expression of progesterone degradation enzyme 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), which represents functional luteolysis. The expressions of both galectin-1 and galectin-3 remarkably increased in the structurally regressing CL, which vigorously expressed 20alpha-HSD and contained abundant apoptotic luteal cells. Ultrastructurally, galectin-1- and galectin-3-immunoreactive cells were identified as fibroblasts and infiltrating macrophages, respectively. In addition, some populations of luteal cells themselves expressed galectin-3 in regressing CL and formed unique demarcation membranes in the cytoplasm, showing a non-typical apoptotic feature. Ovary of adult mice with repeated estrus cycles contained CL of three different generations. Among them, the old CL formed during previous estrus cycles consisted of galectin-3-positive luteal cells. The galectin-3-positive old CL was resistant to apoptosis and seemed to be eliminated by a mechanism different from apoptosis. The stage- and cell-specific expression of galectin in CL suggests its differential contribution to luteolysis, and this expression may be mediated by major regulatory molecules of CL function, prolactin and/or prostaglandin F2alpha.