[Expression of recombinant proteins in the milk of transgenic animals]

Assessment of microchimerism following somatic cell nuclear transfer and natural pregnancies in goats

Microchimerism is defined as the presence of a small population of cells or DNA in 1 organism originated from a genetically different organism. It is well established that this phenomenon occurs in humans and mice as cells are exchanged between mother and fetus during gestation. Currently, no information is available about the presence of maternal microchimerism in goats, and the only published study is limited to an evaluation of fetal and fetal-fetal microchimerism in blood samples following natural breeding. In order to determine whether bidirectional fetal-maternal cell or DNA trafficking occurs in goats, we assessed: 1) fetal microchimerism in surrogates that gave birth to somatic cell nuclear transfer (SCNT)-derived transgenic offspring (n = 4), 2) maternal microchimerism following natural breeding of SCNT-derived transgenic does with a nontransgenic buck (n = 4), and 3) fetal-fetal microchimerism in nontransgenic twins of transgenic offspring (n = 3). Neomycin-resistance gene (NEO) gene was selected as the marker to detect the presence of the αMHC-TGF-β1-Neo transgene in kidney, liver, lung, lymph node, and spleen. We found no detectable maternal or fetal-fetal microchimerism in the investigated tissues of nontransgenic offspring. However, fetal microchimerism was detected in lymph node tissue of one of the surrogate dams carrying a SCNT pregnancy. These results indicate occurrence of cell trafficking from fetus to mother during SCNT pregnancies. The findings of this study have direct implications on the use and disposal of nontransgenic surrogates and nontransgenic offspring.

Methods for collecting milk from mice

Mouse models offer unique opportunities to study mammary gland biology and lactation. Phenotypes within the mammary glands, especially those caused by genetic modification, often arise during lactation, and their study requires the collection of adequate volumes of milk. We describe two approaches for collecting milk from lactating mice. Both methods are inexpensive, are easy to use in the laboratory or classroom, are non-invasive, and yield adequate volumes of milk for subsequent analyses.

Dexamethasone enhances interaction of endogenous annexin 1 with L-selectin and triggers shedding of L-selectin in the monocytic cell line U-937

(1) L-selectin, constitutively expressed by leukocytes, is involved in the initial binding of leukocytes to activated endothelium. Anti-inflammatory drugs like glucocorticoids can induce shedding of L-selectin, but the mechanism is still unknown. Annexin 1, a protein whose synthesis and externalization/secretion are induced during the inflammatory response, has been proposed as a mediator of the anti-inflammatory actions of glucocorticoids. (2) The monocytic cell line U-937 strongly expresses Annexin 1 after 24 h of phorbol 12-myristate 13-acetate (PMA, 1 nm) treatment and externalizes/releases the protein after additional 16 h of dexamethasone (1 microm) treatment. (3) This study investigated the possible regulation of cell surface L-selectin shedding by endogenous Annexin 1, and its role in glucocorticoid-induced L-selectin shedding in the U-937 cell line. (4) PMA- and dexamethasone treatment-induced L-selectin shedding was potentially mediated by Annexin 1, since neutralizing antibodies against Annexin 1 reduced dexamethasone- and Annexin 1-induced shedding. (5) Immunoprecipitation and binding assays provided support for the suggestion that this effect could be mediated by an interaction between externalized Annexin 1 and L-selectin. Such interaction involved the N-terminal domain of Annexin 1 and was calcium-dependent. Confocal microscopy studies demonstrated increased colocalization of Annexin 1 and L-selectin on the cell surface. (6) Overall, our study provides new insights into the potential role of endogenous ANXA1 as a mediator of dexamethasone-induced L-selectin shedding, which may contribute to the anti-inflammatory activity of glucocorticoids.

Regulation of human protein C gene expression by the mouse WAP promoter

A 4.1 kb mouse whey acidic protein (mWAP) promoter was cloned from a C57BL/6 cosmid library. The tissue-specific and developmental pattern of expression of a hybrid gene comprised of the mWAP promoter fragment and the human protein C (HPC) gene was analysed in transgenic mice. The corresponding RNA was detected mainly in the mammary gland, with 'leakage' of expression in the salivary gland and kidney. The developmental pattern of transgene expression differed from that of the endogenous WAP gene. In particular, recombinant HPC (rHPC) transcripts were detected earlier in pregnancy than WAP RNA, with no significant increase during lactation. This indicates that regulatory elements responsible for developmental regulation are located outside the 4.1 kb mWAP gene promoter fragment, or if present, may be subject to position effects. Precocious expression of the transgene did not compromise the health or nursing abilities of transgenic females. Expression of rHPC affected the appearance of the mammary alveoli and alveolar epithelial cells in lactating transgenic mice. The alveoli were less distended and alveolar epithelial cells appeared cuboidal with centrally positioned nuclei. We suggest that the inefficient intracellular processing of rHPC can alter the histological appearance of alveolar epithelial cells in the transgenic mammary gland.