Proteoglycans and glycosaminoglycans during maturation of the mouse mammary gland.

The mammary gland underwent morphological changes starting from a simple tubular structure, developing into a rich alveolar formation during lactation and ultimately a terminally differentiated tubular complex in retired breeders. Early stages of development, male and virgin mouse glands, were rich in hyaluronic acid but also contained smaller amounts of a low sulfate heparan. During lactation, there was a dramatic increase in sulfated glycosaminoglycan, in particular dermatan sulfate. Retired breeders were characterized by a highly sulfated heparan. These changes in glycosaminoglycan composition were analogous to changes seen in many embryologic tissues during morphogenesis and reflect the alterations in tissue modeling. The changes in glycosaminoglycans were reflective of the change observed in solubilized membrane associated proteoglycan. During lactation there was a dramatic increase in the content of dermatan sulfate proteoglycan. Both the dermatan sulfate and the proteoglycan which predominate during lactation was isolated as a complex with a small RNA, called pgRNA. The pgRNA was found only in-the lactating stage and not in virgin mice or retired breeders.