[Endothelial function: role, assessment and limits]. / La fonction endothéliale : rôle, méthodes d'évaluation et limites.

For several years, detecting and preventing cardiovascular diseases have become a major issue. Different methods have been developed to evaluate endothelial function. Endothelial dysfunction is one of the first steps leading to atherosclerosis. This review presents an insight into endothelial function, the interests of its assessment and methods for studying endothelial function. To date, the vascular endothelium must be considered as a specific organ with its own functions that contribute to the homeostasis of the cardiovascular system. Endothelial dysfunction typically corresponds to a decrease of nitric oxide NO bioavailability. Biological or physico-chemical methods may be used to assess dysfunction. Biological methods allow measuring NO metabolites and pro-inflammatory and vasoconstrictor mediators released by the endothelium. The physico-chemical methods include intra-coronary injections, plethysmography, flow-mediated dilation (FMD), digital plethysmography and optical techniques using laser (laser Doppler single-point, laser Doppler imager, laser speckle contrast imaging) that can be coupled with provocation tests (iontophoresis, microdialysis, post-ischemic hyperemia, local heating). The principle of each technique and its use in clinical practice are discussed. Studying endothelial dysfunction is a particularly promising field because of new drugs being developed. Nevertheless, assessment methodology still needs further development to enable reliable, non-invasive, reproducible, and inexpensive ways to analyze endothelial dysfunction.

All trans retinoic acid abrogates spontaneous monocytic growth in juvenile chronic myelomonocytic leukaemia.

INTRODUCTION: All trans retinoic acid, the active metabolite of vitamin A, exerts profound effects on cell differentiation. On normal myeloid progenitors, retinoids switch the differentiation program of granulo-macrophagic progenitors towards the granulocytic lineage and consequently reduce CFU-M colony formation. Bone marrow and peripheral blood mononuclear cells from children with Juvenile Chronic Myelomonocytic Leukaemia show typical spontaneous monocytic growth. We questioned whether in this disease, retinoids could switch myelomonocytic growth and inhibit the abnormal CFU-M colony proliferation. METHODS: Ten JCML samples were studied in the presence of ATRA in methyl cellulose colony assay, before (CFU-C) or after (pre-CFU) liquid suspension culture. RESULTS: In vitro characteristics of JCML such as spontaneous monocytic growth in the absence of growth factor was noted in all patients. In the presence of leucocyte-conditioned medium, nine samples showed only CFU-M growth and one sample CFU-GM growth. Incubation with ATRA inhibited CFU-M colony formation in nine cases. Enhancement of granulocytic differentiation (CFU-G) was noted in nine cases. ATRA also inhibited CD34+ JCML monocytic growth and GM-CSF hypersensitivity. CONCLUSION: These data suggest that, in JCML progenitors, retinoid pathways are functional and inhibition of immature monocytic progenitors cells may be achieved with retinoids, without impeding granulocytic cell growth.

The efficiency of different IRESs (internal ribosomes entry site) in monocistronic mRNAS.

The IRES from poliovirus and from encephalomyocarditis virus (EMCV) added between the cap and the AUG initiator codon were strong inhibitors of chloramphenicol acetyltransferase gene expression in three different cell types. The poliovirus IRES also inhibited bGH (bovine growth hormone) cDNA expression in the HC11 mammary cell line when added between the rabbit whey acidic gene promoter and the cDNA whereas the HTLV-1 IRES showed a stimulatory effect in the same situation. RNA stem loops were added before HTLV-1 (SUR) and the BiP (Immunoglobulin heavy-chain Binding Protein) IRESs followed by the firefly luciferase gene under the control of Rous sarcoma virus (RSV) promoter. The RNA loops abolished the expression of the reporter gene almost completely. These data suggest that the different IRESs may favour or inhibit translation of monocistronic mRNA.

The stimulation of gene expression by the R region from HTLV-1 and BLV.

The 5' untranslated regions (5'UTR) of mRNA are known to stimulate or inhibit more or less translation. SR alpha, an association of SV40 early gene promoter and of the R region plus the first 39 nucleotides of the U5 region (designated as R) from the human T-cell leukemia virus (HTLV-1) is currently used to stimulate expression of various coding regions. Its effect is considered to take place at the translational level. In all studies published so far, the R region was associated with the promoter and 5'UTR from SV40 early genes. In the present work, the role of SV40 5'UTR and HTLV-1R region was evaluated separately using different promoters, reporter genes and cells. Both SV40 5'UTR (SU) and R region (R) from HTLV-1 stimulated separately the expression of adjacent reporter genes. When associated, the SV40 5'UTR and the R region from HTLV-1 (SUR) were a more potent stimulator of gene expression and their effects were more than additive. This effect was very potent in HeLa and HC11 cells and almost inexistent in CHO and COS 7 cells. It was of various intensity in other cell types including bird and fish cells. The presence of SUR in gene constructs favoured the accumulation of the mRNAs. SUR stimulated gene expression when added between the cap and the initiation codon. Unexpectedly, SUR was never inhibitory. SUR can therefore be considered essentially as potent and specific stimulator of gene expression favoring mRNA accumulation.

Association of the 5'HS4 sequence of the chicken beta-globin locus control region with human EF1 alpha gene promoter induces ubiquitous and high expression of human CD55 and CD59 cDNAs in transgenic rabbits.

Whatever its field of application, animal transgenesis aims at a high level of reproducible and stable transgene expression. In the case of xenotransplantation, prevention of hyperacute rejection of grafts of animal origin requires the use of organs expressing human inhibitors of complement activation such as CD55 (DAF) and CD59. Pigs transgenic for these molecules have been produced, but with low and variable levels of expression. In order to improve cDNA expression, a vector containing the 5'HS4 region from the LCR of the chicken beta-globin locus and the promoter and the first intron from the human EF1 alpha gene, was used to co-express human CD55 and CD59 cDNAs in transgenic rabbits. The transgenic lines with the 5'HS4 region displayed dramatically enhanced CD55 and CD59 mRNA concentrations in brain, heart, kidney, liver, lung, muscle, spleen and aortic endothelial cells in comparison with the transgenic lines without the 5'HS4 region. In the absence of the 5'HS4 region, only some of the transgenic lines displayed specific mRNAs and at low levels. Human CD55 and CD59 proteins were detectable in mononuclear cells from transgenic rabbits although at a lower level than in human mononuclear cells. On the other hand, primary aortic endothelial cells from a bi-transgenic line were very efficiently protected in vitro against human complement-dependent lysis. Transgenic rabbits harbouring the two human inhibitors of complement activation, CD55 and CD59, can therefore be used as new models in xenotransplantation. Moreover, the vector containing the 5'HS4 region from the LCR of the chicken beta-globin locus seems appropriate not only for xenotransplantation but also for any other studies involving transgenic animals in which cDNAs have to be expressed at a high level in all cell types.

Ovine chorionic somatomammotrophin (oCS) production by isolated cotyledon cells from sheep in early and mid gestation: auto-regulation by recombinant oCS.

We report the ability of sheep placental cotyledonary cells, isolated at different periods of pregnancy (40 to 90 days) to produce ovine chorionic somatomammotrophin (oCS) in in vitro culture conditions. This oCS production increased gradually with stage of pregnancy. Endogenous oCS net production by isolated placental cells was increased, in a dose-dependent manner, by addition of recombinant oCS (roCS). This effect was not observed after addition of recombinant ovine growth hormone. The roCS effect was more potent on cells collected during early pregnancy. Specific immunoprecipitation of oCS revealed that roCS treatment was associated with an increased dose-dependent incorporation of [35S]methionine-[35S]cysteine. These findings provide evidence that oCS may act in a paracrine/autocrine manner to up-regulate its own production during early gestation. We suggest that this autoregulation may be associated with morphological and functional differentiation of the trophoblast during the growth of the placenta.

Effect of intercistronic length on internal ribosome entry site (IRES) efficiency in bicistronic mRNA.

Specific structures found in the mRNA of picornavirus are known to allow a cap-independent translation. These structures, named internal ribosome entry sites (IRES), are also able to favor translation of the second cistron in bicistronic mRNAs. Their mechanism of action is not well understood. In the present study, two IRESs have been used: the IRES from poliovirus and a newly discovered IRES (SUR) composed of the 5' P untranslated sequence from SV40 early genes, the R structure, and a small part of the U5 region from the human leukemia virus-1 (HTLV-1). The bicistronic constructs containing the firefly luciferase gene as the first cistron and the chloramphenicol acetyltransferase (CAT) as the second cistron were driven by the Rous sarcoma virus (RSV) promoter and contained the early gene SV40 terminator. All the resulting plasmids were tested by transfection in HeLa and CHO cells. In the bicistronic mRNAs without IRES, the expression of the CAT gene was dependent on the distance between the two cistrons. The maximum efficiency in the expression of the second cistron was obtained when the intercalating RNA was composed of 30 to 90 nucleotides. This expression was deeply reduced when the intercalating fragment contained 8 or 300 nucleotides and was undetectable with 500 nucleotides. Unexpectedly, the luciferase mRNA was almost not expressed when the intercalating RNA was of 8 or 30 nucleotides. Expression of the luciferase gene occurred when the intercistronic RNA fragment was of 80 nucleotides and it became lower at 300 and 500 nucleotides. The same observations were done when the poliovirus or the SUR IRESs were added after the intercistronic spacers. However, expression of the CAT gene was amplified by both IRESs. When the CAT cistron preceded by the poliovirus or SUR IRES was introduced within luciferase cistron, 316 nucleotides before its termination codon, the IRESs were able to initiate translation of the following CAT gene irrespectively of the mRNA luciferase reading frame. Moreover, with all these constructs the highest expression level of the CAT cistron did not exceed 10% of that obtained with the same vector carrying only the CAT cistron. To identify a possible relation between the IRESs and the cap site, the CAT cistron preceded or not with an IRES was introduced 210 nucleotides downstream of the AUG codon of the luciferase gene (i.e., 258 nucleotides from the cap site) and 100 nucleotides after an added UAG termination codon. Expression of the CAT gene was not modified by the addition of the poliovirus IRES but it was strongly stimulated by the SUR IRES (the level of expression corresponded to 65% of that obtained with the same vector carrying only the CAT cistron). These results suggest that there is a cooperation between the cap and the SUR IRES and not the poliovirus IRES to stimulate translation. These data indicate that IRESs must be introduced in precise position to allow an efficient expression of the second cistron in bicistronic mRNAs.

Cloning, structural organization and tissue-specific expression of the rabbit transferrin gene.

We cloned the rabbit transferrin (rTf) cDNA and gene, and quantified the expression of the rTf gene at the RNA level in various organs. The tissue-specific pattern of expression of rTf gene is different to those in other species, with a high expression in mammary gland and kidney. The exon/intron structure of the rTf gene (17 exons/16 introns) is similar to those of transferrins from other species. The sequence of the rTf cDNA already published is corrected and lengthened in the 5' region, and a likely polymorphism is documented.

Recombinant human extracellular superoxide dismutase produced in milk of transgenic rabbits.

Expression of human extracellular superoxide dismutase (EC-SOD), a glycosylated, tetrameric metalloprotein, was targeted to the lactating mammary gland of transgenic rabbits. Efficient expression of the recombinant whey acidic protein/ec-sod gene was achieved and up to 3 mg ml-1 of the enzyme was secreted into the milk. Rabbit milk-produced recombinant EC-SOD was primarily found in the whey and purified by a two-step chromatographic method. To evaluate the rabbit milk-produced human EC-SOD, comparisons with native and Chinese hamster ovary cell (CHO)-produced EC-SOD were performed. All proteins were tetrameric and N-glycosylated. The behaviour on SDS-PAGE and size-exclusion chromatography indicated that the masses, and thereby the extent of post-translational modification of the proteins was similar. The monosaccharide composition of both recombinant EC-SOD variants was analysed and indicated similarities in the attached N-glycans on the two proteins. Furthermore, the peptide maps of the three EC-SOD variants revealed that all proteins had similar polypeptide backbones.

Porcine Dax-1 gene: isolation and expression during gonadal development.

The identification of XY females carrying a duplication of a region of the X chromosome (Xp21) led to the hypothesis that a double dose of a gene in the duplicated region causes sex reversal (DSS; dosage sensitive sex reversal). A gene isolated from this region, named DAX-1 (DSS-AHC critical region on the X), encodes a new member of the nuclear hormone receptor family. Here, we describe the isolation of porcine Dax-1 and the analysis of its pattern of expression both during foetal development and in several adult tissues. Dax-1 is expressed in the adrenals, the pituitary gland and the gonads at various stages of differentiation. In gonads, Dax-1 expression starts between 21 and 23 days post coitum in both XX and XY urogenital ridges then continues to be expressed until adult age. The expression in these tissues indicates the involvement of DAX-1 in the development and the function of the reproductive system at multiple levels.

The effect of prolactin on casein kinase II, MAP kinase and PKC in rabbit mammary cells and Nb2 rat lymphoid cells.

Prolactin induces milk protein gene expression in rabbit primary mammary cells without any concomitant cell multiplication. Prolactin or other lactogenic hormones is the major inducer of cell division in the rat lymphoid Nb2 cells. In Nb2 cells, prolactin also rapidly induces the expression of the c-myc gene, and beta-actin and stathmin gene expression is induced more slowly. The possible involvement of casein kinase II (CKII), mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) in these process is not well known. The present work was undertaken to evaluate the effect of prolactin on these protein kinases and to determine the possible involvement of these enzymes in the activity of several genes under the control of the hormone. In rabbit mammary cells, prolactin did not alter CKII activity but did transiently stimulate MAP kinase activity. Prolactin also stimulated Ca(2+)-independent PKC. This effect was visible after 10 min and was maintained for at least 24 hr. Staurosporine, an inhibitor of PKC and of several tyrosine kinases altered Ca(2+)-independent PKC only moderately. In contrast, GF 109203X, a potent and specific inhibitor of PKC, abrogated almost all PKC activity. Staurosporine, but not GF 109203X, prevented the induction of the casein gene by prolactin. In Nb2 cells, prolactin induced a slow stimulation of CKII activity. The hormone did not induce MAP kinase activity. Prolactin stimulated Ca(2+)-independent PKC over periods of 24 hr. GF 109203X, but not staurosporine, inhibited PKC activity, whereas staurosporine but not GF 109203X, inhibited the induction of Nb2 cell multiplication and the accumulation of c-myc, beta-actin and stathmin mRNAs. From these data, it can be concluded that (1) the stimulation of CKII by prolactin in Nb2 cells is concomitant with cell multiplication: (2) MAPK stimulation is not necessary for prolactin to induce Nb2 cell multiplication; and (3) PKC is stimulated in mammary and Nb2 cells, but this stimulation is not required for prolactin to stimulate casein, c-myc, beta-actin and stathmin gene expression and Nb2 cell division.

Expression of the growth hormone gene in ovine placenta: detection and cellular localization of the protein.

In several species, placenta has been found to express GH-related proteins. In the ovine placenta, such a protein, ovine chorionic somatommamotropin, has been described, but its involvement in the fetal/placental growth process is not clearly established. The aim of this study was to investigate the occurrence of another GH-related peptide in the ovine placenta. Placental extracts (days 30-140 of pregnancy) showed GH immunoreactivity between days 35-70. SDS-PAGE analysis of these extracts indicated that this immunoreactivity corresponded to 22- and 28-kDa proteins. GH-like immunoreactivity was localized on cotyledonary frozen sections in the syncytium and the trophectoderm. Northern blot analysis of placental RNA showed the expression of GH-hybridizing transcripts migrating to the same position as that of GH pituitary messenger RNA (mRNA). Those transcripts were highly expressed between days 40 and 50. Their sequence analysis showed the existence of three GH mRNA (GHP1, GHP2, and GHP3). GHP1 is identical to pituitary GH mRNA and probably codes for the 22-kDa protein. GHP2 and GHP3 encode the same protein, which differs from GHP1 by four amino acids. This study establishes the expression of GH gene and GH-immunoreactive proteins in the ovine placenta.

OZF gene expression in growing mouse and rabbit mammary gland and in rabbit mammary cells and Nb2 cells under prolactin action.

The OZF gene identified recently is expressed in a few cell types and particularly in mammary cell but not in fibroblasts. This gene is expressed more abundantly in several mammary tumor cell lines than in normal cells. In the present work, OZF mRNA concentration was evaluated in rabbit and mouse mammary gland during the pregnancy-lactation-weaning cycle. The OZF mRNA concentration was at its highest level during the first part of pregnancy and decreased at parturition. It was maintained at its lowest level throughout lactation. Prolactin which induces mammary gland growth and milk synthesis in vivo did not stimulate OZF gene expression. In the Nb2 lymphoid cell line, prolactin, which is a compulsory growth factor, did not alter OZF mRNA concentration. These data suggest that OZF may be involved in some way in mammary gland growth. Moreover, OZF does not appear to be a key gene for the induction of cell multiplication. OZF gene expression might negatively control, to some extent, mammary cell differentiation.

The effects of various kinase and phosphatase inhibitors on the transmission of the prolactin and extracellular matrix signals to rabbit alpha S1-casein and transferrin genes.

In all species, milk protein genes are specifically expressed in the mammary gland under the control of lactogenic hormones and extracellular matrix. In rabbit, casein gene expression is induced by prolactin alone and this induction is amplified by extracellular matrix. Transferrin gene expression is induced by extracellular matrix in the absence of hormones. The transduction mechanisms of prolactin and extracellular matrix to milk protein genes is only partly known. The present study has been undertaken to determine if protein kinases and phosphatases are involved in these mechanisms. Rabbit primary mammary cells were cultured in three different conditions (i) directly on floating collagen I, (ii) on plastic after a trypsinization to remove endogenous extracellular matrix, and (iii) on floating collagen I after a trypsinization to restore a functional extracellular matrix. In these culture conditions, prolactin and several protein kinase and phosphatase inhibitors were added to the medium. The expression of alpha S1-casein and transferrin genes was evaluated using Northern blotting analysis. In cells cultured directly on collagen I, staurosporine, quercetin and 6-dimethylaminopurine strongly inhibited prolactin action of alpha S1-casein gene whereas herbimycin A was only partly inhibitory. An erbstatin analogue, tyrosine phosphate, 1(5 isoquinolylsulphonyl) 2-methylpiperazine and GF 109 203 X did not alter prolactin action. The inhibitors which inhibited prolactin action when cells were directly cultured on collagen I were also those which prevented the induction of alpha S1-casein gene expression when cells were cultured on plastic in the absence of extracellular matrix. The induction of transferrin gene by the extracellular matrix was inhibited slightly by quercetin. Okadaic acid, phenylarsine oxide and sodium pervanadate which inhibit Ser/Thr and Tyr phosphatase inhibitors were unable to mimic prolactin action on alpha S1-casein gene expression. On the contrary, these inhibitors prevented prolactin action. These data suggest that a cascade including protein kinases and phosphatases for Ser/Thr and Tyr phosphate is involved in the transduction of the prolactin message from its receptor to casein genes. The signal delivered to the mammary cells by the extracellular matrix is quite different, possibly involving another cascade of protein kinases.

The effect of various introns and transcription terminators on the efficiency of expression vectors in various cultured cell lines and in the mammary gland of transgenic mice.

Various combinations of promoters, introns and transcription terminators were used to drive the expression of bovine growth hormone (bGH) cDNA in different cell types. In constructs containing the human cytomegalovirus (hCMV) promoter and the SV40 late genes terminator, the intron from SV40 genes (VP1) was much more efficient, than the intron from the early genes (t). The synthetic intron SIS generated by the association of an adenovirus splice donor and an immunoglobulin G splice acceptor showed the highest activity. The respective potency of these introns was similar in several mammalian (CHO, HC11 and COS) and fish (TO2 and EPC) cells. The rabbit whey acidic protein (WAP) gene promoter was highly efficient to drive the expression of bGH gene in the HC11 mammary cell lines. In contrast, the bGH cDNA under the control of the same promoter was much less efficiently expressed when the SV40 VP1 intron and transcription terminator were used. The rabbit WAP gene and the human GH gene terminators did not or only moderately enhanced the expression of the construct WAP bGH cDNA. Introduction of a promoter sequence from the mouse mammary tumor virus (MMTV) LTR in the VP1 intron increased very significantly the expression of the WAP bGH cDNA. Although several of these vectors showed high potency when expressed stably in HC11 cells, all of them were only moderately efficient in transgenic mice. These data indicate that the VP1 and the SIS introns may be used to express foreign cDNAs with good efficiency in different cell types. The addition of an enhancer within an intron may still reinforce its efficiency. However, transfection experiments, even when stable expression is carried out, are poorly predictive of the potential efficiency of a vector in transgenic animals.

Polymeric-Ig receptor gene expression in rabbit mammary gland during pregnancy and lactation: evolution and hormonal regulation.

The polymeric immunoglobulin receptor (poly Ig-R) mediates transcytosis of IgA and IgM antibodies produced by local plasma cells across epithelial cells of mucosal and glandular tissues. Gene expression of the poly-Ig R was analyzed in rabbit mammary gland during pregnancy and lactation. The poly Ig-R was expressed as early as day 8 (G8) of gestation and mRNA accumulation remained low until about G18. From G21, the mRNA abundance increased and reached steady state levels approximately 5-fold higher at day 15 of lactation (L15) when compared to basal levels at G8. The hormonal regulation of poly-Ig receptor gene expression was assessed in mammary organ cultures. Poly-Ig R mRNA accumulation in mammary explants cultured for 24 or 48 h in the presence of ovine prolactin (oPRL) was significantly increased to a maximal 4-fold level at 1 microgram ml-1 of oPRL. Estradiol (100 pg ml-1) or progesterone (1 microgram ml-1) did not further stimulate poly-Ig R expression. In contrast, their combination resulted in a significant 30-50% decrease of poly-Ig-R mRNA levels. The addition of 1 microgram ml-1 of cortisol to medium in the absence or presence of estradiol or progesterone decreased the amount of poly-Ig-R mRNA. The results suggest that until mid-pregnancy, poly-Ig-R expression is inhibited by elevated progesterone-estradiol concentrations and that the subsequent increase is due to the concomitant decrease of the two circulating steroids and the increase of serum prolactin levels.

Protein kinase C is not necessary for beta-casein gene induction by prolactin in HC11 mouse mammary cells.

HC11 mouse mammary cells cultured in the presence of insulin, cortisol and prolactin for 24 h accumulated beta-casein mRNA. When the specific inhibitor of protein kinase C, GF 109203 X, was added to the medium with the hormones, the accumulation of beta-casein mRNA was unaltered, although the protein kinase C activity was almost completely suppressed. This suggests that protein kinase C is not strictly necessary for prolactin to induce milk protein gene expression.

Stathmin gene expression in mammary gland and in Nb2 cells.

Mammary gland growth occurs essentially during pregnancy and induction of milk synthesis is triggered at parturition. Prolactin is mammogenic in vivo but only marginally in vitro. Prolactin induces milk synthesis in vivo and in cultured mammary cells. Prolactin is also strictly required for the multiplication of the rat lymphoid Nb2 cells. Stathmin is an ubiquitous and highly conserved phosphoprotein which seems to be involved in the intracellular mechanisms which trigger cell multiplication and differentiation. In the present study, the concentration of stathmin mRNA has been evaluated during the pregnancy-lactation-weaning cycle in mouse and rabbit. Stathmin mRNA appeared at its highest level during pregnancy and it was almost undetectable during lactation. Prolactin injected into mid-pregnant rabbits induced milk synthesis and this effect was not accompanied by any modification of stathmin mRNA concentration. In cultured primary rabbit mammary cells, prolactin induced casein gene expression without any alteration of stathmin mRNA concentration. In Nb2 cells, prolactin induced a progressive increase of stathmin mRNA concentration. This effect was not significant until after 4 h of prolactin action. These data suggest that stathmin is involved in mammary and Nb2 cell multiplication but may not be necessary for mammary cell differentiation.

Variation of transferrin mRNA concentration in the rabbit mammary gland during the pregnancy-lactation-weaning cycle and in cultured mammary cells. A comparison with the other major milk protein mRNAs.

The concentration of transferrin mRNA was evaluated during pregnancy and lactation in rabbit mammary gland and liver using northern blot and dot blot assays. Transferrin mRNA was present in the virgin rabbit mammary gland and its concentration increased as pregnancy proceeded, with a major enhancement after day 15. A high concentration was reached 3 days after parturition, with no additional increase during lactation and with a marked decline after weaning. During the same period, the concentration of transferrin mRNA showed only a very weak variation in liver. This mRNA was six times more abundant in mammary gland than in liver of lactating rabbit. The accumulation of transferrin mRNA in the mammary gland was concomitant with the accumulation of alpha s1-, beta-, kappa-casein and WAP (whey acidic protein) mRNAs. The concentration of glyceraldehyde 3-phosphate dehydrogenase mRNA, taken as a non-inducible control mRNA, declined progressively during pregnancy to reach its lower level in lactation. These observations suggest that casein, WAP and transferrin mRNAs are subjected to a similar control mechanism in vivo, at least in the second half of pregnancy and during lactation. Experiments carried out in vitro using isolated rabbit epithelial mammary cells cultured on collagen I gel indicated that transferrin mRNA was abundant and only weakly inducible by the lactogenic hormones insulin, cortisol and prolactin, as opposed to caseins and WAP mRNAs. R5020, an analogue of progesterone, inhibited at most very slightly the accumulation of alpha s1-casein mRNA in the presence of prolactin and it did not reduce the expression of transferrin gene.(ABSTRACT TRUNCATED AT 250 WORDS)

High level production of human growth hormone in the milk of transgenic mice: the upstream region of the rabbit whey acidic protein (WAP) gene targets transgene expression to the mammary gland.

The 5' flanking region (6.3 kb) of the rabbit WAP (rWAP) gene possesses important regulatory elements. This region was linked to the human growth hormone (hGH) structural gene in order to target transgene expression to the mammary gland. Thirteen lines of transgenic mice were produced. Milk could be collected from six lines of transgenic mice. In five of them, hGH was present in the milk at high concentrations ranging from 4 to 22 mg ml-1. hGH produced by the mammary gland comigrated with hGH of human origin. It was biologically active, and through its prolactin-like activity induced lactogenesis when introduced into mammary culture media. Two of these mouse lines were studied further. hGH mRNA was only detected in the mammary gland during lactation. In the seven other transgenic lines, hGH was present in the blood of cyclic females. The prolactin-like effect of hGH in these mice probably induced female sterility, and milk could therefore not be obtained. In two lines studied in more detail, the mammary gland was the main organ producing hGH, even in cyclic mice. Low ectopic expression was detected in other organs which varied from one line to the other. This was probably due to the influence on the transgene of the site of integration into the mouse genome. In the 13 lines studied, high mammary-specific hGH expression was not correlated to the transgene copy number. The rWAP-hGH construct thus did not behave as an independent unit of transcription. However, it can be concluded that the 6.3 kb flanking region of the rWAP gene contains regulatory elements responsible for the strong mammary-specific expression of hGH transgene, and that it is a good candidate to control high levels of foreign protein gene expression in the mammary gland of lactating transgenic animals.