Hormone-dependent expression of the ovine beta-lactoglobulin gene

The comparative biology of whey proteins

Lactational strategies and associated development of the young have been studied in a diverse range of species, and comparative analysis allows common trends and differences to be revealed. The whey fraction contains a vast number of proteins, many of which have not been assigned a function. However, it is expected that an understanding of the comparative biology of these proteins may provide some promise in assigning a function to the major whey proteins. Whey acidic protein is a major component of the whey fraction that has been studied across a range of species, revealing conservation of gene structure, whereas regulation and temporal expression patterns vary. This review focuses primarily on comparative analysis of whey acidic protein, highlighting gene structure, developmental and hormonal regulation, and potential functional roles for this protein. In addition, the contrasting regulation and secretion profiles of several other major whey proteins are discussed.

Nucleosome organisation of the beta-lactoglobulin gene. Transcription complex formation

In most mammals, the major whey protein beta-lactoglobulin (beta lg) represents a marker for tissue-specific, temporally regulated gene expression in the mammary gland. Prolactin, the major lactogenic stimulus which activates beta lg expression acts through a cytoplasmic signalling cascade ending in the activation of the transcription factor STAT5. Although much is known about the complexities of this signalling cascade, little is known about how this transcription factor functions within the context of chromatin. Using DNaseI as a probe of chromatin structure we have identified temporally regulated elements within the ovine beta lg gene domain. The appearance of these hypersensitive sites accompanies changes in expression state of the beta lg gene. Changes in DNaseI hypersensitivity at the proximal promoter region, while reflecting STAT5 activation, is not dependent upon STAT5 interaction at this site. We have mapped the nucleosome positions over the entire beta lg gene, both in vitro using the monomer extension assay and in vivo using cuprous phenanthroline to probe for nucleosome-linker positions. The specific positioning pattern detected, which reflects strong sequence-directed positioning over the proximal promoter, complement the STAT5 consensus sites within this region. The comparison of both the functional and chromatin data enables a model for beta lg gene transcription to be developed.

An in vitro approach to ruminant mammary gland biology

This review discusses both fundamental and applied in vitro studies on ruminant mammary gland biology and summarizes progress made over the last decade in development of in vitro techniques to study growth, function and pathology of the mammary gland. The advantages and limitations of different in vitro systems are considered including explant cultures, primary cell cultures and immortalized lines of mammary-derived cells from cow, sheep and goat. The cell growth, differentiation and response to lactogenic hormones and growth factors are discussed as well as the relevance of the cell behavior in different culture conditions.