A marsupial beta-lactoglobulin gene: characterization and prolactin-dependent expression

Area of Science:

• Comparative genomics
• Mammalian lactation
• Gene expression regulation

Background:

• Beta-lactoglobulin (BLG) is a major whey protein in the milk of many mammals.
• Understanding BLG evolution and regulation provides insights into lactation diversity.
• Marsupial milk composition and regulation offer a unique perspective on mammalian evolution.

Purpose of the Study:

• To analyze the tammar wallaby beta-lactoglobulin (BLG) cDNA and amino acid sequences.
• To investigate the regulation of BLG gene expression during lactation in tammar wallabies.
• To compare BLG sequence and expression with that of eutherian mammals.

Main Methods:

• Sequence analysis of tammar wallaby beta-lactoglobulin cDNA.
• Northern analysis of total mammary RNA to detect BLG transcripts.
• Quantification of BLG mRNA in hormone-stimulated mammary gland explants.

Main Results:

• Tammar wallaby BLG sequence exhibits extensive divergence from eutherian BLGs, with conserved structural and ligand-binding residues.
• Two BLG transcripts were identified, arising from differential polyadenylation signal usage.
• BLG mRNA levels increase during late lactation, correlating with milk production and fat content.
• Maximal BLG gene induction in late pregnancy is prolactin-dependent, independent of other eutherian lactation-initiating hormones.

Conclusions:

• Tammar wallaby BLG has evolved distinct sequence features compared to eutherian orthologs.
• BLG gene expression in marsupials is regulated differently than in eutherians, with prolactin being the key inducer.
• These findings highlight the evolutionary divergence in milk protein function and lactation regulation between marsupials and eutherians.