Question

Difference in gene expression of virgin and lactational mammary epithelial cells

Answer 1

Explanation:

Introduction

Mammary gland development during the pregnancy cycle is characterized by successive phases of cell growth, differentiation, high metabolic activity and apoptosis. At the ultrastructural level this includes dramatic changes in tissue architecture, involving ductal epithelial branching and morphogenesis, invasion of tissue compartments, vascularization and subsequent organized remodelling. These events are highly reproducible and strictly controlled at the transcriptional level by circulating hormones and locally derived factors [1]. Thus, many transcription factors have been shown either to directly affect this developmental program or to exhibit altered activity at specific stages in the pregnancy cycle [1].

Our laboratory has focused on the role of transcription factors in postlactational regression of the gland after weaning. Involution can be divided into at least two phases [2-4], broadly comprising the following: an initial reversible phase whereby the gland maintains its gross morphology but undergoes a substantial increase in the rate of epithelial cell apoptosis [5]; and a secondary irreversible phase, which involves the destruction of basement membrane by matrix metalloproteinases, phagocytic clearance of milk, and apoptotic bodies and alveolar collapse [6]. Immune cells are present at all stages of mammary development, including involution [7], but the precise role of the immune system during postlactational regression has yet to be fully established. Many genes have been shown to be differentially regulated during involution [5,8,9]. However, there has been no comprehensive analysis of gene expression in mammary involution.

Microarray analysis has had a major impact on our understanding of the transcriptional basis of complex biological systems. Normal tissue development and homeostasis has been studied in a variety of mouse tissues, including retina [10], liver [11], pancreas [12], uterus [13] and mammary gland [14].

The few microarray studies of normal mouse mammary gland described in the literature have either focused on early stages in the developmental cycle [14], or have used mammary data as a tool for illustrating methods