Uterine differentiation as a foundation for subsequent fertility

Uterine differentiation in cattle and sheep begins prenatally, but is compl eted postnatally. Mechanisms regulating this process are not well defined. However, studies of urogenital tract development in murine systems, particu larly those involving tissue recombination and targeted gene mutation, indi cate that the ideal uterine organizational programme evolves epigenetically through dynamic cell-cell and cell-matrix interactions that define the mic roenvironmental context within which gene expression occurs and may ensure adult tissue stability. In the cow and ewe, transient postnatal exposure of the developing uterus to steroids can produce immutable changes in adult u terine tissues that may alter the embryotrophic potential of the uterine en vironment. Thus, success of steroid-sensitive postnatal events supporting u terine growth and development can dictate the functional potential of the a dult uterus. Studies to determine effects of specific steroidal agents on p atterns of uterine development during defined neonatal periods, as well. as the functional consequences of targeted neonatal steroid exposure in the a dult uterus, should enable identification of critical developmental mechani sms and determinants of uterine integrity and function. Extreme adult uteri ne phenotypes (lesion models) created in cattle and sheep by strategic post natal steroid exposure hold promise as powerful tools for the study of fact ors affecting uterine function and the rapid identification of novel uterin e genes.