Production of low-lactose milk by ectopic expression of intestinal lactase in the mouse mammary gland

The Lithbea Domain

The tree of life is the evolutionary metaphor for the past and present connections of all cellular organisms. Today, to speak of biodiversity is not only to speak of archaea, bacteria, and eukaryotes, but they should also consider the "new biodiversity" that includes viruses and synthetic organisms, which represent the new forms of life created in laboratories. There is even a third group of artificial entities that, although not living systems, pretend to imitate the living. To embrace and organize all this new biodiversity, I propose the creation of a new domain, with the name Lithbea (from life-on-the-border entites) The criteria for inclusion as members of Lithbea are: i) the acellular nature of the living system, ii) its origin in laboratory manipulation, iii) showing new biological traits, iv) the presence of exogenous genetic elements, v) artificial or inorganic nature. Within Lithbea there are two subdomains: Virworld (from virus world) which includes all viruses, regarded as lifeless living systems, and classified according to the International Committee on Taxonomy of Viruses (ICTV), and ii) Humade (from human-made) which includes all synthetic organisms and artificial entities. The relationships of Lithbea members to the three classical woesian domains and their implications are briefly discussed.

Effect of Polyethylene Glycol-Induced Molecular Crowding on the Enzymatic Activity and Thermal Stability of β-Galactosidase from Kluyveromyces lactis

Here, we report the effect of polyethylene glycol (PEG₆₀₀₀)-induced molecular crowding (MC) on the catalytic activity and thermal stability of Kluyveromyces lactis β-galactosidase (β-Gal). The β-Gal-catalyzed hydrolysis of o-nitrophenyl-β-d-galactopyranoside followed a Michaelian kinetics at [PEG₆₀₀₀] ≤ 25% w/v and positive cooperativity at higher concentrations (35% w/v PEG₆₀₀₀). Compared with dilute solutions, in the MC media, β-Gal exhibited stronger thermal stability, as shown by the increase in the residual activity recovered after preincubation at high temperatures (e.g., 45 °C) and by the slower inactivation kinetics. Considering the effects of water thermodynamic activity on the reaction kinetics and protein structure and the effect of the exclusion volume on protein conformation, we suggest that changes in the protein oligomerization state and hydration could be the responsible for the behavior observed at the highest MC levels assayed. These results could be relevant and should be taken into account in industrial food processes applying β-Gal from K. lactis.

β-Galactosidase gene codon optimization results in post-transcriptional enhancement of expression

OBJECTIVE

lacZ encodes for β-galactosidase within the galactose operon of bacterial cells. When used as a reporter gene, bacterial "β-galactosidase" expression is often insufficient for detection in mammalian cells. We intended to optimize the lacZ codon usage according to the most frequently used codons for the seven major proteins in cow's milk, in order to pave a way for the enhancement of transgenic genes expression in eukaryotes.

RESULTS

We constructed modified lacZ (named olacZ) according to optional codons used for proteins expressed in cow's milk. The expression of lacZ and olacZ was then compared in HC11 (a murine mammary gland epithelial line), 293T, HeLa, Cos7, and NIH 3T3 cells. While there was no significant difference at the mRNA level between lacZ and olacZ (P > 0.05). The quantification of β-galactosidase activity and in situ staining experiments showed a 1.2-fold to 3.3-fold expression improvement when comparing olacZ with lacZ. The levels of β-galactosidase expression at the protein levels from olacZ were approximately 9.2-fold and 2.4-fold respectively for Cos7 and HC11 cells. Furthermore, a 1.9-fold tendency of enhanced expression of olacZ in mammary gland during lactation was observed in transgenic-olacZ mice.

CONCLUSION

This study demonstrates an alternative choice for improving lacZ reporter expression in eukaryotes, especially in the mammary gland of cattle or goats.

Ca2+-activated Cl− channel currents in mammary secretory cells from lactating mouse

The Cl− secretion via Ca2+-activated Cl− channel (CaCC) is critical for fluid secretion in exocrine glands like the salivary gland. Also in the mammary gland, it has been hypothesized that CaCC plays an important role in the secretion of Cl− and aqueous phase of milk. However, there has been no evidence for the functional expression of CaCC in native mammary secretory (MS) cells of lactating animals. We therefore assessed membrane current in MS cells that were freshly isolated from lactating mice using whole cell patch-clamp techniques. In MS cells, we detected CaCC current that exhibited the following characteristics: 1) Ca2+-dependent activation at the concentrations of submicromolar range; 2) voltage-dependent activation; 3) slow kinetics for activation and deactivation; 4) outward rectification of the steady-state current; 5) anion permeability in the sequence of I− > NO3− > Br− > Cl− >> glutamate; 6) inhibition by Cl− channel blockers (niflumic acid, DIDS, and CaCCinh-A01). These characteristics of native CaCC current were similar to reported characteristics of heterologously expressed TMEM16A. RT-PCR analyses showed the expression of multiple CaCC channels including TMEM16A, Best1, and Best3 in the mammary glands of lactating mice. Immunohistochemical staining revealed the localization of TMEM16A protein at the apical membrane of the MS cells. Collectively, our data strongly suggest that MS cells functionally express CaCC, which is at least partly constituted by TMEM16A. The CaCC such as TMEM16A at the apical membrane of the MS cells may influence the quantity and/or quality of milk.

Strategies to enable the adoption of animal biotechnology to sustainably improve global food safety and security

The ability to generate transgenic animals has existed for over 30 years, and from those early days many predicted that the technology would have beneficial applications in agriculture. Numerous transgenic agricultural animals now exist, however to date only one product from a transgenic animal has been approved for the food chain, due in part to cumbersome regulations. Recently, new techniques such as precision breeding have emerged, which enables the introduction of desired traits without the use of transgenes. The rapidly growing human population, environmental degradation, and concerns related to zoonotic and pandemic diseases have increased pressure on the animal agriculture sector to provide a safe, secure and sustainable food supply. There is a clear need to adopt transgenic technologies as well as new methods such as gene editing and precision breeding to meet these challenges and the rising demand for animal products. To achieve this goal, cooperation, education, and communication between multiple stakeholders-including scientists, industry, farmers, governments, trade organizations, NGOs and the public-is necessary. This report is the culmination of concepts first discussed at an OECD sponsored conference and aims to identify the main barriers to the adoption of animal biotechnology, tactics for navigating those barriers, strategies to improve public perception and trust, as well as industry engagement, and actions for governments and trade organizations including the OECD to harmonize regulations and trade agreements. Specifically, the report focuses on animal biotechnologies that are intended to improve breeding and genetics and currently are not routinely used in commercial animal agriculture. We put forward recommendations on how scientists, regulators, and trade organizations can work together to ensure that the potential benefits of animal biotechnology can be realized to meet the future needs of agriculture to feed the world.

Genetically engineering milk

It has been thirty years since the first genetically engineered animal with altered milk composition was reported. During the intervening years, the world population has increased from 5bn to 7bn people. An increasing demand for protein in the human diet has followed this population expansion, putting huge stress on the food supply chain. Many solutions to the grand challenge of food security for all have been proposed and are currently under investigation and study. Amongst these, genetics still has an important role to play, aiming to continually enable the selection of livestock with enhanced traits. Part of the geneticist's tool box is the technology of genetic engineering. In this Invited Review, we indicate that this technology has come a long way, we focus on the genetic engineering of dairy animals and we argue that the new strategies for precision breeding demand proper evaluation as to how they could contribute to the essential increases in agricultural productivity our society must achieve.

Expression of human growth hormone in the milk of transgenic rabbits with transgene mapped to the telomere region of chromosome 7q

The advent of transgenic technology has provided methods for the production of pharmaceuticals by the isolation of these proteins from transgenic animals. The mammary gland has been focused on as a bioreactor, since milk is easily collected from lactating animals and protein production can be expressed at very high levels, including hormones and enzymes. We demonstrate here the expression pattern of recombinant human growth hormone (rhGH) in transgenic rabbits carrying hGH genomic sequences driven by the rat whey acidic protein (WAP) promoter. The transgene was mapped to the q26-27 telomere region of chromosome 7q by fluorescence in situ hybridization (FISH). Nearly 30 % of the F1 generation demonstrated the presence of transgene. The recombinant growth hormone was detected in the milk of the transgenic rabbit females, but not in serum, up to the level of 10 μg/ml. Ectopic expression of the transgene in the brain, heart, kidney, liver, and salivary gland was not observed, indicating that a short sequence of rat WAP promoter (969 bp) contained essential sequences directing expression exclusively to the mammary gland. The biological activity of recombinant growth hormone was measured by immunoreactivity and the capability to stimulate growth of the hormone-dependent Nb211 cell line.

The construction and expression of lysine-rich gene in the mammary gland of transgenic mice

Lysine is the limiting amino acid in cereal grains, which represent a major source of human food and animal feed worldwide, and is considered the most important of the essential amino acids. In this study, β-casein, αS2-casein, and lactotransferrin cDNA clone fragments encoding lysine-rich peptides were fused together to generate a lysine-rich (LR) gene and the mammary gland-specific expression vector pBC1-LR-NEO(r) was constructed. Transgenic mice were generated by pronuclear microinjection of the linearized expression vectors harboring the LR transgene. The transgenic mice and their offspring were examined using multiplex polymerase chain reaction (PCR), Southern blotting, reverse transcriptase-PCR, in situ hybridization, and Western blotting techniques. Our results showed that the LR gene was successfully integrated into the mouse genome and was transmitted stably. The specific LR gene expression was restricted to the mammary gland, active alveoli of the transgenic female mice during lactation. The lysine level of the two transgenic lines was significantly higher than that of nontransgenic controls (p<0.05). In addition, the growth performance of transgenic pups was enhanced by directly feeding them the LR protein-enriched transgenic milk. Our results demonstrated that lysine-rich gene was successfully constructed and expressed in mammary gland of transgenic mice. This study will provide a better understanding of how mammary gland expression systems that increase the lysine content of milk can be applied to other mammals, such as cows.

Precision genetics for complex objectives in animal agriculture

Indirect modification of animal genomes by interspecific hybridization, cross-breeding, and selection has produced an enormous spectrum of phenotypic diversity over more than 10,000 yr of animal domestication. Using these established technologies, the farming community has successfully increased the yield and efficiency of production in most agricultural species while utilizing land resources that are often unsuitable for other agricultural purposes. Moving forward, animal well-being and agricultural sustainability are moral and economic priorities of consumers and producers alike. Therefore, these considerations will be included in any strategy designed to meet the challenges produced by global climate change and an expanding world population. Improvements in the efficiency and precision of genetic technologies will enable a timely response to meet the multifaceted food requirements of a rapidly increasing world population.

[Applications of genetically modified animals]

The first transgenic animals, mice, were obtained in 1980. The techniques of gene transfer had to be adapted to obtain transgenic animals with an acceptable yield in about fifteen species. When the yield is low (low rate of random integration and targeted integration via homologous recombination), genetic modifications must be achieved in intermediate cells able to participate to the development of chimeric transgenic animals (ES cells, EG cells, iPS obtained by the dedifferentiation of somatic cells) or in somatic cells used as nuclear donor to generate transgenic clones. Various tools make possible a marked increase of homologous recombination efficiency (meganucleases and ZFN), or a gene inactivation at the genome level (direct or conditional knock out) or at the mRNA level (interfering RNAs). Vectors allow a more reliable transgene expression. Genetically modified animals are used mainly to obtain information on biological functions and human diseases. Transgenic animals produce recombinant pharmaceutical proteins in milk and soon in egg white. Pig organs adapted to be tolerated by patients might be tested in humans in five years. The projects based on the use of transgenesis to improve animal production are presently few. Transgenic salmon with accelerated growth might be on the market when their possible escape in oceans will be controlled.

Safety assessment of food products from r-DNA animals

Recombinant-DNA (transgenic) animals intended for food production are approaching the market. Among them, recombinant-DNA fishes constitute the most advanced case. As a result, intergovernmental organizations are working on guidelines which would eventually become international standards for national food safety assessments of these products. This article reviews the emerging elements for the food safety assessment of products derived from recombinant-DNA animals. These elements will become highly relevant both for researchers and regulators interested in developing or analyzing recombinant-DNA animals intended to be used in the commercial elaboration of food products. It also provides references to science-based tools that can be used to support food safety assessments. Finally, it proposes recommendations for the further development of biosafety assessment methodologies in this area.

Animal transgenesis: state of the art and applications

There is a constant expectation for fast improvement of livestock production and human health care products. The advent of DNA recombinant technology and the possibility of gene transfer between organisms of distinct species, or even distinct phylogenic kingdoms, has opened a wide range of possibilities. Nowadays we can produce human insulin in bacteria or human coagulation factors in cattle milk. The recent advances in gene transfer, animal cloning, and assisted reproductive techniques have partly fulfilled the expectation in the field of livestock transgenesis. This paper reviews the recent advances and applications of transgenesis in livestock and their derivative products. At first, the state of art and the techniques that enhance the efficiency of livestock transgenesis are presented. The consequent reduction in the cost and time necessary to reach a final product has enabled the multiplication of transgenic prototypes around the world. We also analyze here some emerging applications of livestock transgenesis in the field of pharmacology, meat and dairy industry, xenotransplantation, and human disease modeling. Finally, some bioethical and commercial concerns raised by the transgenesis applications are discussed.

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.

Preparation of recombinant proteins in milk to improve human and animal health

Milk is a very abundant source of proteins for animal and human consumption. Milk composition can be modified using transgenesis, including exogenous gene addition and endogenous gene inactivation. The study of milk protein genes has provided researchers with regulatory regions capable of efficiently and specifically driving the expression of foreign genes in milk. The projects underway are aimed at modifying milk composition, improving its nutritional value, reducing mammary infections, providing consumers with antipathogen proteins and preparing purified recombinant proteins for pharmaceutical use. The present paper summarises the current progress in this field.

Endless versatility in the biotechnological applications of Kluyveromyces LAC genes

Most microorganisms adapted to life in milk owe their ability to thrive in this habitat to the evolution of mechanisms for the use of the most abundant sugar present on it, lactose, as a carbon source. Because of their lactose-assimilating ability, Kluyveromyces yeasts have long been used in industrial processes involved in the elimination of this sugar. The identification of the genes conferring Kluyveromyces with a system for permeabilization and intracellular hydrolysis of lactose (LAC genes), along with the current possibilities for their transfer into alternative organisms through genetic engineering, has significantly broadened the industrial profitability of lactic yeasts. This review provides an updated overview of the general properties of Kluyveromyces LAC genes, and the multiple techniques involving their biotechnological utilization. Emphasis is also made on the potential that some of the latest technologies, such as the generation of transgenics, will have for a further benefit in the use of these and related genes.

Production and Processing of Milk from Transgenic Goats Expressing Human Lysozyme in the Mammary Gland

The potential for applying biotechnology to benefit animal agriculture and food production has long been speculated. The addition of human milk components with intrinsic antimicrobial activity and positive charge to livestock milk by genetic engineering has the potential to benefit animal health, as well as food safety and production. We generated one line of transgenic goats as a model for the dairy cow designed to express human lysozyme in the mammary gland. Here we report the characterization of the milk from 5 transgenic females of this line expressing human lysozyme in their milk at 270 microg/mL or 68% of the level found in human milk. Milk from transgenic animals had a lower somatic cell count, but the overall component composition of the milk and milk production were not different from controls. Milk from transgenic animals had a shorter rennet clotting time and increased curd strength. Milk of such nature may be of benefit to the producer by influencing udder health and milk processing.

Use of transgenic animals to improve human health and animal production

Contents Transgenic animals are more widely used for various purposes. Applications of animal transgenesis may be divided into three major categories: (i) to obtain information on gene function and regulation as well as on human diseases, (ii) to obtain high value products (recombinant pharmaceutical proteins and xeno-organs for humans) to be used for human therapy, and (iii) to improve animal products for human consumption. All these applications are directly or not related to human health. Animal transgenesis started in 1980. Important improvement of the methods has been made and are still being achieved to reduce cost as well as killing of animals and to improve the relevance of the models. This includes gene transfer and design of reliable vectors for transgene expression. This review describes the state of the art of animal transgenesis from a technical point of view. It also reports some of the applications in the medical field based on the use of transgenic animal models. The advance in the generation of pigs to be used as the source of organs for patients and in the preparation of pharmaceutical proteins from milk and other possible biological fluids from transgenic animals is described. The projects in course aiming at improving animal production by transgenesis are also depicted. Some the specific biosafety and bioethical problems raised by the different applications of transgenesis, including consumption of transgenic animal products are discussed.

Genetically engineered livestock: closer than we think?

The potential of biotechnology to benefit production agriculture has long been speculated. Whereas many transgenic crops have been produced and commercialized, there has yet to be any implementation of genetically engineered livestock. A recent publication by Wall et al. represents one of the first reports to bring the potential of genetic engineering closer to realization by improving disease resistance in dairy cattle: a practical advantage to both the producer and animal.

Membrane topology modulates beta-galactosidase activity against soluble substrates

The effect of bio-surfaces of contrasting curvature, on the kinetic parameters of ortho-nitrophenyl-beta-D-galactopiranoside hydrolysis catalyzed by E. coli beta-galactosidase, was investigated. The self-aggregating state and structure of the amphiphiles (Phosphatidylcholine, Lubrol-PX, Triton X-100, DocNa, SDS and CTAB) were inferred from their c.m.c. values and light-scattering measurements. Low curvature phosphatidylcholine or mixed phosphatidylcholine-detergent vesicles increased V(max) without affecting K(M). High curvature micellar structures containing ionic detergents modulated negatively the enzyme activity (decreased or abolished V(max) and increased K(M)). Neither micelles containing non-ionic detergents nor the amphiphiles in a monomeric form, affected enzyme activity. CTAB at a concentration below its c.m.c but incorporated into a bilayer, became an activator (K(M) decreased respect to the control). Non-enzymatic interfacial hydrolysis of the substrate was discarded. Enzyme-membrane interaction and membrane elasticity, were evaluated using monomolecular layers at the air-water interface. Beyond particular molecular structures, topology affected the direction of the modulatory effects exerted by these amphiphiles on beta-galactosidase activity.

The use of recombinase proteins to generate transgenic large animals

The endogenous properties of recombinase proteins allow them to associate with and bind DNA to catalyze homologous recombination. These endogenous properties of cellular recombination enzymes may be useful to the field of transgenesis. The production of transgenic animals, in particular livestock, is an inefficient process by both conventional pronuclear microinjection techniques and nuclear transfer. Furthermore, the use of pronuclear microinjection is currently limited to the random addition of genes and does not allow for the replacement of an endogenous gene with a more desired one. The functions of cellular recombination enzymes have been exploited to develop a technique that is compatible with pronuclear microinjection and may make the process of generating transgenic livestock more efficient while also enabling the targeting of homologous chromosomal genes. In our hands, transgenic animals generated by the pronuclear microinjection of various recombinase protein-coated DNA fragments led to a higher than expected birth rate as well as transgene integration frequency. Most founder animals generated were likely mosaic, indicating that integration occurred after cell division. The presence of multiple related genes makes detection of any recombination event difficult. Overall, this technique is a straightforward, rapid, and efficient procedure that can be applied to any segment of DNA and any microinjection apparatus, and is less labor intensive than nuclear transfer.

The methods to generate transgenic animals and to control transgene expression

Transgenic animals have been used for years to study gene function and to create models for the study of human diseases. This approach has become still more justified after the complete sequencing of several genomes. Transgenic animals are ready to become industrial bioreactors for the preparation of pharmaceuticals in milk and probably in the future in egg white. Improvement of animal production by transgenesis is still in infancy. Despite its intensive use, animal transgenesis is still suffering from technical limitations. The generation of transgenics has recently become easier or possible for different species thanks to the use of transposons or retrovirus, to incubation of sperm which DNA followed by fertilization by intracellular sperm injection or not and to the use of the cloning technique using somatic cells in which genes have been added or inactivated. The Cre-LoxP system is more and more used to withdraw a given sequence from the genome or to target the integration of a foreign DNA. The tetracycline system has been improved and can more and more frequently be used to obtain faithful expression of transgenes. Several tools: RNA forming a triple helix with DNA, antisense RNA including double strand RNA inducing RNA interference and ribozymes, and also expression of proteins having a negative transdominant effect, are tentatively being improved to inhibit specifically the expression of host or viral genes.All these techniques are expected to offer experimenters new and more precise models to study gene function even in large animals. Improvement of breeding by transgenesis has become more plausible including through the precise allele replacement in farm animals.

Lethal hypoglycemic ketosis and glyceroluria in mice lacking both the mitochondrial and the cytosolic glycerol phosphate dehydrogenases

The activities of either the mitochondrial or cytosolic glycerol phosphate dehydrogenase (mGPD, cGPD) plus that of glycerol kinase are required for the use of glycerol in aerobic metabolism and gluconeogenesis. A knockout mouse lacking mGPD has reduced body weight and fertility but shows remarkably normal liver and muscle metabolite levels. The BALB/cHeA mouse strain, which lacks cGPD, breeds well and is phenotypically normal, although it demonstrates metabolite abnormalities in certain tissues. Crosses were made between these two strains, and mice were generated that lacked both dehydrogenases. These mice, although active and nursing well for several days, failed to grow, and usually died within the first week. Liver glycerol phosphate levels were elevated 30-fold, whereas liver ATP, ADP, and AMP levels were reduced by 30-40%. Plasma glycerol was elevated 30- to 50-fold to 30-50 mm, and urine glycerol exceeded 0.45 m (4% w/v). GPD-deficient mice were hypoglycemic, had a 50% increase in plasma free fatty acids, and developed ketonuria within the first day of life. Uncoupling protein-1 mRNA in brown adipose tissue was reduced 60%. These mice share some features of both glycerol kinase deficiency and hereditary fructose intolerance, suggesting the phenotype may be due to the combined effects of the loss of a gluconeogenic substrate, the osmotic effects of glycerol, and the metabolic effects of the accumulation of a phosphorylated metabolite.

Normal thyroid thermogenesis but reduced viability and adiposity in mice lacking the mitochondrial glycerol phosphate dehydrogenase

The mitochondrial glycerol phosphate dehydrogenase (mGPD) is important for metabolism of glycerol phosphate for gluconeogenesis or energy production and has been implicated in thermogenesis induced by cold and thyroid hormone treatment. mGPD in combination with the cytosolic glycerol phosphate dehydrogenase (cGPD) is proposed to form the glycerol phosphate shuttle, catalyzing the interconversion of dihydroxyacetone phosphate and glycerol phosphate with net oxidation of cytosolic NADH. We made a targeted deletion in Gdm1 and produced mice lacking mGPD. On a C57BL/6J background these mice showed a 50% reduction in viability compared with wild-type littermates. Uncoupling protein-1 mRNA levels in brown adipose tissue did not differ between mGPD knockout and control pups, suggesting normal thermogenesis. Pups lacking mGPD had decreased liver ATP and slightly increased liver glycerol phosphate. In contrast, liver and muscle metabolites were normal in adult animals. Adult mGPD knockout animals had a normal cold tolerance, normal circadian rhythm in body temperature, and demonstrated a normal temperature increase in response to thyroid hormone. However, they were found to have a lower body mass index, a 40% reduction in the weight of white adipose tissue, and a slightly lower fasting blood glucose than controls. The phenotype may be secondary to consequences of the obligatory production of cytosolic NADH from glycerol metabolism in the mGPD knockout animal. We conclude that, although mGPD is not essential for thyroid thermogenesis, variations in its function affect viability and adiposity in mice.

Over-expression of the murine pIgR gene in the mammary gland of transgenic mice influences the milk composition and reduces its nutritional value

The polymeric immunoglobulin receptor (pIgR) transports dimeric IgA (dIgA) across epithelial cells lining mucosal and glandular tissues, including the mammary gland. Four transgenic mouse lines were generated, overexpressing the murine pIgR gene in the epithelial cells of their mammary glands under control of the regulatory sequences of the bovine alphas1-casein gene. Ten to 270-fold over-expression of the IgA receptor was achieved. The pIgR transgenic line 3644, having the highest pIgR transgene expression, had a markedly altered milk composition compared to non-transgenic mice. In the other three transgenic lines the milk composition, other than SC levels, were not changed. In the milk of line 3644 a protein of 31 kD was lacking and a new protein of 11 kD appeared at relatively high levels. The 31 kD protein was identified as k-casein and the 11 kD protein as serum amyloid A-1 (SAA1). The nutritional value of the milk of females from transgenic line 3644 was dramatically impaired as shown by the retarded growth and development of the pups, leading to death two weeks after birth.

Introduction of the human growth hormone gene into the guinea pig mammary gland by in vivo transfection promotes sustained expression of human growth hormone in the milk throughout lactation

We tested the feasibility of transfecting mammary tissue in vivo with an expression plasmid encoding the human growth hormone (hGH) gene, under the control of the cytomegalovirus promoter. Guinea pig mammary glands were transfected with plasmid DNA infused through the nipple canal and expression was monitored in control and transfected glands by radioimmunoassay of milk samples for hGH. Sustained expression of hGH throughout lactation was attained with a polyion transfection complex shown to be optimal for the transfection of bovine mammary cells, in vitro. However, contrary to expectations, hGH expression was consistently 5- to 10-fold higher when DEAE-dextran was used alone for transfection. Thus polyion complexes which are optimal for the transfection of cells in vitro may not be optimal in vivo. The highest concentrations of hGH in milk were obtained when glands were transfected within 3 days before parturition. This method may have application for studying the biological role or physical properties of recombinant proteins expressed in low quantities, or for investigating the regulation of gene promoters without the need to construct viral vectors or produce transgenic animals.

Species differences in the sites of cleavage of pro-lactase to lactase supports lack of selective pressure

The pro-sequences in pro-lactase-phlorizin hydrolase (LPH) are needed for lactase to proceed past the ER, but are irrelevant as to the enzymatic activities. Hence, in all species removal of the pro- sequences (or most of them) must take place after the ER. Contrary to this, the details of the removal of these pro-sequences are to be expected to differ in the various species, since they are not subjected to selective pressure. Using site-directed mutagenesis we investigated processing in rabbit. The first cleavage occurs by furin (or furin-like PCs) and takes place at R-A-A-R(349) in the pro-sequence, generating the known 180 kDa intermediate. Replacing R(349) by Q results in a mutant which is not cleaved but nevertheless transported to the cell surface as demonstrated by immunofluorescence. Further processing of either the 180 kDa intermediate or the mutant is not directly mediated by furin-like PCs, but involves (also) other proteases. These results demonstrate that formation of the 180 kDa intermediate, consistently found only in rabbits, but not in man, is not essential for lactase transport: in all likelihood lack of selective pressure has led to species-specific processing of pro-LPH.