Characterization and partial purification of bovine alpha-lactalbumin and beta-casein produced in milk of transgenic mice

A Comparative Review of the Extrinsic and Intrinsic Factors Regulating Lactose Synthesis

Milk is critical for the survival of all mammalian offspring, where its production by a mammary gland is also positively associated with its lactose concentration. A clearer understanding of the factors that regulate lactose synthesis stands to direct strategies for improving neonatal health while also highlighting opportunities to manipulate and improve milk production and composition. In this review we draw a cross-species comparison of the extra- and intramammary factors that regulate lactose synthesis, with a special focus on humans, dairy animals, and rodents. We outline the various factors known to influence lactose synthesis including diet, hormones, and substrate supply, as well as the intracellular molecular and genetic mechanisms. We also discuss the strengths and limitations of various in vivo and in vitro systems for the study of lactose synthesis, which remains an important research gap.

Designer milk

Dairy biotechnology is fast gaining ground in the area of altering milk composition for processing and/or animal and human health by employing nutritional and genetic approaches. Modification of the primary structure of casein, alteration in the lipid profile, increased protein recovery, milk containing nutraceuticals, and replacement for infant formula offer several advantages in the area of processing. Less fat in milk, altered fatty acid profiles to include more healthy fatty acids such as CLA and ω‐fats, improved amino acid profiles, more protein, less lactose, and absence of β‐lactoglobulin (β‐LG) are some opportunities of “designing” milk for human health benefits. Transgenic technology has also produced farm animals that secrete in their milk, human lactoferrin, lysozyme, and lipase so as to simulate human milk in terms of quality and quantity of these elements that are protective to infants. Cow milk allergenicity in children could be reduced by eliminating the β‐LG gene from bovines. Animals that produce milk containing therapeutic agents such as insulin, plasma proteins, drugs, and vaccines for human health have been genetically engineered. In order to cater to animal health, transgenic animals that express in their mammary glands, various components that work against mastitis have been generated. The ultimate acceptability of the “designer” products will depend on ethical issues such as animal welfare and safety, besides better health benefits and increased profitability of products manufactured by the novel techniques.

An expression profile of human alpha-lactalbumin in the milk of transgenic mouse

Five female transgenic mice were produced by microinjection using a construct made up of a 7.3-kb-5' flanking region and a 2.0-kb coding region of human alpha-lactalbumin, as well as a 227-bp 3'-flanking region from bovine growth hormone gene. A founder female expressed human alpha-lactalbumin as much as 0.3 g per liter of its milk, approximately a 3-fold increase in the total alpha-lactalbumin concentration of the transgenic mouse milk. Compared with the normal mice, the expression profile of the halpha-Lac transgene in the transgenics is different during the lactation, showing low level in the first 3 days and becoming increased from day 4, then gradually reaching and stabilizing at the highest level from day 13. In addition, the milk yielding volume in the transgenics tended to be higher than in normal mice, suggesting higher concentrations of alpha-lactalbumin might boost more milk output.

Processing and localization of bovine beta-casein expressed in transgenic soybean seeds under control of a soybean lectin expression cassette

We have examined the processing and subcellular localization of a chimeric gene consisting of the bovine milk protein, beta-casein, under the control of a soybean seed lectin promoter and its 32 amino acid signal sequence in the seeds of transgenic soybean plants. The beta-casein expressed in developing soybean seeds is a doublet with apparent molecular weight slightly smaller than the bovine beta-casein and expression of the protein was highest in immature cotyledons. The casein proteins were purified from the immature soybean seeds by immunoaffinity chromatography and were analyzed by two-dimensional gel electrophoresis, blotting, and amino terminal sequencing. The N-terminal sequences of both of the doublet soybean casein polypeptides were identical to the N-terminal sequence of the bovine beta-casein indicating that the 32 amino acid lectin signal sequence was cleaved precisely from the chimeric protein in developing soybean seeds. Analysis of the purified soybean beta-casein polypeptides by mass spectrometry (MALDI-MS) showed that they are not phosphorylated. Absence of added phosphate groups is the cause of the size difference between the soybean beta-casein and native bovine beta-casein protein. Immunolocalization experiments showed that the casein protein was found in the protein storage vacuoles (PSV) in developing and mature soybean seeds. The precise removal of the 32 amino acid lectin amino terminal sequence from the chimeric lectin-casein fusion suggests that the lectin expression cassette can be used for production of pharmaceutical or other recombinant proteins of added value in the developing soybean seed.

Transgenic animals and nutrition research

Transgenic animals are useful tools for the study of biological functions of proteins and secondary gene products synthesized by the action of protein catalysts. Research in nutrition and allied fields is benefiting from their use as models to contrast normal and altered metabolism. Although food, nutritional products, and ingredients from transgenic animals have not yet reached consumers, the technologies for their production are maturing and yielding exciting results in experimental and farm animals. Regulatory governmental bodies are already issuing guidelines and legislation in anticipation of the advent of these products and ingredients. This review summarizes available technology for the production of transgenic animals, discusses their scientific and commercial potential, and examines ancillary issues relevant to the field of nutrition.