Mutant mouse models and their contribution to our knowledge of corpus luteum development , function and regression

The corpus luteum is a unique organ, which is transitory in nature. The development, maintenance and regression of the corpus luteum are regulated by endocrine, paracrine and autocrine signaling events. Defining the specific mediators of luteal development, maintenance and regression has been difficult and often perplexing due to the complexity that stems from the variety of cell types that make up the luteal tissue. Moreover, some regulators may serve dual functions as a luteotropic and luteolytic agent depending on the temporal and spatial environment in which they are expressed. As a result, some confusion is present in the interpretation of in vitro and in vivo studies. More recently investigators have utilized mutant mouse models to define the functional significance of specific gene products. The goal of this mini-review is to identify and discuss mutant mouse models that have luteal anomalies, which may provide some clues as to the significance of specific regulators of corpus luteum function. Introduction The corpus luteum is an important byproduct of the ovulating follicle. It is a transitory, hormonally regulated organ that consists of a heterogeneous cell population. Unlike the follicle, the different cell types are not segregated into distinct compartments, but are highly integrated. The steroidogenic cells synthesize progesterone for the establishment and maintenance of pregnancy. Other cell types include the endothelial cells and immune cells, typically thought to play supportive roles. There is evidence to suggest that the endothelial cells and the immune cells play an active role in luteal formation, maintenance and regression [1]. The vascular endothelial cells make up a large portion of the corpus luteum, whereas the immune cells vary in number dependent upon the stage of the luteal phase or pregnancy [1-3]. Studies designed to elucidate the contributions of one or more of the luteal cell types are often difficult to interpret. More often than not these studies are based on in vitro cell culture models. Primary cultures of dispersed luteal tissue or enriched populations of specific cell types provide some opportunity for investigators to delineate potential signaling pathways, which may be engaged in response to a specific stimulus. Outcomes derived from in vitro studies are important but are often subject to criticism. For example, in vitro studies tend to favor one cell type or another. Moreover, the cell-cell interactions that are present in a multidimensional environment in vivo are removed when experiments are performed in a two dimensional field in vitro (eg, tissue culture dish). What effect this has on an outcome is not always fully appreciated and cannot be directly extrapolated to the in vivo model. For example prostaglandin F2α (PGF2α) is primarily considered a Published: 10 November 2003 Reproductive Biology and Endocrinology 2003, 1:87 Received: 15 April 2003 Accepted: 10 November 2003 This article is available from: http://www.rbej. com/content/1/1/87 © 2003 Henkes et al; licensee BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.