Immune status of decidual macrophages is dependent on the CCL2/CCR2/JAK2 pathway during early pregnancy

PROBLEM

Decidual macrophages (dMφ ) play an important role in the formation of maternal-fetal immune tolerance. However, factors that influence the immune status of dMφ and the related potential mechanisms have not been elucidated to date.

METHOD OF STUDY

The gene transcription in dMφ , decidual stromal cells (DSCs), extravillous trophoblasts (EVTs), and peripheral monocytes (pMo) from human samples were measured using real-time polymerase chain reaction (PCR). Monocyte-DSC co-culture was established to explore whether DSCs influenced dMφ polarization via C-C motif ligand 2 (CCL2)-C-C chemokine receptor (CCR2) binding using flow cytometry. In vivo, changes in dMφ percentage and M1 and M2 marker expression after treatment with CCR2 or Janus kinase 2 (JAK2) inhibitor were detected with flow cytometry. Embryo resorption percentages in the above groups were also analyzed.

RESULTS

We found that dMφ were an M1/M2 mixed status at the maternal-fetal interface during early pregnancy. CCL2 influenced the immune status of dMφ in an autocrine and paracrine manner. As a downstream regulator of CCR2 and triggers the Stat3 pathway, JAK2 was found to be essential for dMφ homeostasis in vivo. JAK2 inhibitor decreased the dMφ proportion and attenuated Ki67, CD36, CD86, CD206, TNF, and IL-10 expression in dMφ at E8.5 d. Moreover, CCR2-JAK2 pathway inhibition decreased the width of the placental labyrinth layer, further influencing the pregnancy outcome.

CONCLUSION

The M1/M2 mixed immune status of dMφ was regulated by DSCs via CCR2, and the CCL2/CCR2/JAK2 pathway was essential for the immune status of dMφ and the outcome of early pregnancy.

BCKDK regulates the TCA cycle through PDC in the absence of PDK family during embryonic development

Pyruvate dehydrogenase kinases (PDK1-4) inhibit the TCA cycle by phosphorylating pyruvate dehydrogenase complex (PDC). Here, we show that PDK family is dispensable for murine embryonic development and that BCKDK serves as a compensatory mechanism by inactivating PDC. First, we knocked out all four Pdk genes one by one. Surprisingly, Pdk total KO embryos developed and were born in expected ratios but died by postnatal day 4 because of hypoglycemia or ketoacidosis. Moreover, PDC was phosphorylated in these embryos, suggesting that another kinase compensates for PDK family. Bioinformatic analysis implicated branched-chain ketoacid dehydrogenase kinase (Bckdk), a key regulator of branched-chain amino acids (BCAAs) catabolism. Indeed, knockout of Bckdk and Pdk family led to the loss of PDC phosphorylation, an increase in PDC activity and pyruvate entry into the TCA cycle, and embryonic lethality. These findings reveal a regulatory crosstalk hardwiring BCAA and glucose catabolic pathways, which feed the TCA cycle.

Embryonic demise caused by targeted disruption of a cysteine protease Dub-2

Background

A plethora of biological metabolisms are regulated by the mechanisms of ubiquitination, wherein this process is balanced with the action of deubiquitination system. Dub-2 is an IL-2-inducible, immediate-early gene that encodes a deubiquitinating enzyme with growth regulatory activity. DUB-2 presumably removes ubiquitin from ubiquitin-conjugated target proteins regulating ubiquitin-mediated proteolysis, but its specific target proteins are unknown yet.

Methodology/Principal Findings

To elucidate the functional role of Dub-2, we generated genetically modified mice by introducing neo cassette into the second exon of Dub-2 and then homologous recombination was done to completely abrogate the activity of DUB-2 proteins. We generated Dub-2+/− heterozygous mice showing a normal phenotype and are fertile, whereas new born mouse of Dub-2−/− homozygous alleles could not survive. In addition, Dub-2−/− embryo could not be seen between E6.5 and E12.5 stages. Furthermore, the number of embryos showing normal embryonic development for further stages is decreased in heterozygotes. Even embryonic stem cells from inner cell mass of Dub-2−/− embryos could not be established.

Conclusions

Our study suggests that the targeted disruption of Dub-2 may cause embryonic lethality during early gestation, possibly due to the failure of cell proliferation during hatching process.

Lack of Cul4b, an E3 ubiquitin ligase component, leads to embryonic lethality and abnormal placental development

Cullin-RING ligases (CRLs) complexes participate in the regulation of diverse cellular processes, including cell cycle progression, transcription, signal transduction and development. Serving as the scaffold protein, cullins are crucial for the assembly of ligase complexes, which recognize and target various substrates for proteosomal degradation. Mutations in human CUL4B, one of the eight members in cullin family, are one of the major causes of X-linked mental retardation. We here report the generation and characterization of Cul4b knockout mice, in which exons 3 to 5 were deleted. In contrast to the survival to adulthood of human hemizygous males with CUL4B null mutation, Cul4b null mouse embryos show severe developmental arrest and usually die before embryonic day 9.5 (E9.5). Accumulation of cyclin E, a CRL (CUL4B) substrate, was observed in Cul4b null embryos. Cul4b heterozygotes were recovered at a reduced ratio and exhibited a severe developmental delay. The placentas in Cul4b heterozygotes were disorganized and were impaired in vascularization, which may contribute to the developmental delay. As in human CUL4B heterozygotes, Cul4b null cells were selected against in Cul4b heterozygotes, leading to various degrees of skewed X-inactivation in different tissues. Together, our results showed that CUL4B is indispensable for embryonic development in the mouse.

Erk1 and Erk2 regulate endothelial cell proliferation and migration during mouse embryonic angiogenesis

Angiogenesis is a complex process orchestrated by both growth factors and cell adhesion and is initiated by focal degradation of the vascular basement membrane with subsequent migration and proliferation of endothelial cells. The Ras/Raf/MEK/ERK pathway is required for EC function during angiogenesis. Although in vitro studies implicate ERK1 and ERK2 in endothelial cell survival, their precise role in angiogenesis in vivo remains poorly defined. Cre/loxP technology was used to inactivate Erk1 and Erk2 in endothelial cells during murine development, resulting in embryonic lethality due to severely reduced angiogenesis. Deletion of Erk1 and Erk2 in primary endothelial cells resulted in decreased cell proliferation and migration, but not in increased apoptosis. Expression of key cell cycle regulators was diminished in the double knockout cells, and decreased DNA synthesis could be observed in endothelial cells during embryogenesis. Interestingly, both Paxillin and Focal Adhesion Kinase were expressed at lower levels in endothelial cells lacking Erk1 and Erk2 both in vivo and in vitro, leading to defects in the organization of the cytoskeleton and in cell motility. The regulation of Paxillin and Focal Adhesion Kinase expression occurred post-transcriptionally. These results demonstrate that ERK1 and ERK2 coordinate endothelial cell proliferation and migration during angiogenesis.

E1-L2 Activates Both Ubiquitin and FAT10

Ubiquitination is catalyzed by a cascade of enzymes consisting of E1, E2, and E3. We report here the identification of an E1-like protein, termed E1-L2, that activates both ubiquitin and another ubiquitin-like protein, FAT10. Interestingly, E1-L2 can transfer ubiquitin to Ubc5 and Ubc13, but not Ubc3 and E2-25K, suggesting that E1-L2 may be specialized in a subset of ubiquitination reactions. E1-L2 forms a thioester with FAT10 in vitro, and this reaction requires the active-site cysteine of E1-L2 and the C-terminal diglycine motif of FAT10. Furthermore, endogenous FAT10 forms a thioester with E1-L2 in cells stimulated with tumor necrosis factor-alpha (TNFalpha) and interferon-gamma (IFNgamma), which induce FAT10 expression. Silencing of E1-L2 expression by RNAi blocks the formation of FAT10 conjugates in cells. Deletion of E1-L2 in mice caused embryonic lethality, suggesting that E1-L2 plays an important role in embryogenesis.

Leucine carboxyl methyltransferase-1 is necessary for normal progression through mitosis in mammalian cells

Protein phosphatase 2A (PP2A) is a multifunctional phosphatase that plays important roles in many cellular processes including regulation of cell cycle and apoptosis. Because PP2A is involved in so many diverse processes, it is highly regulated by both non-covalent and covalent mechanisms that are still being defined. In this study we have investigated the importance of leucine carboxyl methyltransferase-1 (LCMT-1) for PP2A methylation and cell function. We show that reduction of LCMT-1 protein levels by small hairpin RNAs causes up to a 70% reduction in PP2A methylation in HeLa cells, indicating that LCMT-1 is the major mammalian PP2A methyltransferase. In addition, LCMT-1 knockdown reduced the formation of PP2A heterotrimers containing the Balpha regulatory subunit and, in a subset of the cells, induced apoptosis, characterized by caspase activation, nuclear condensation/fragmentation, and membrane blebbing. Knockdown of the PP2A Balpha regulatory subunit induced a similar amount of apoptosis, suggesting that LCMT-1 induces apoptosis in part by disrupting the formation of PP2A(BalphaAC) heterotrimers. Treatment with a pan-caspase inhibitor partially rescued cells from apoptosis induced by LCMT-1 or Balpha knockdown. LCMT-1 knockdown cells and Balpha knockdown cells were more sensitive to the spindle-targeting drug nocodazole, suggesting that LCMT-1 and Balpha are important for spindle checkpoint. Treatment of LCMT-1 and Balpha knockdown cells with thymidine dramatically reduced cell death, presumably by blocking progression through mitosis. Consistent with these results, homozygous gene trap knock-out of LCMT-1 in mice resulted in embryonic lethality. Collectively, our results indicate that LCMT-1 is important for normal progression through mitosis and cell survival and is essential for embryonic development in mice.

Mice deficient in heparan sulfate 6-O-sulfotransferase-1 exhibit defective heparan sulfate biosynthesis, abnormal placentation, and late embryonic lethality

Heparan sulfate (HS) plays critical roles in a variety of developmental, physiological, and pathogenic processes due to its ability to interact in a structure-dependent manner with numerous growth factors that participate in cellular signaling. The divergent structures of HS glycosaminoglycans are the result of the coordinate actions of several N- and O-sulfotransferases, C5-epimerase, and 6-O-endosulfatases. We have shown that 6-O-sulfation of the glucosamine residues in HS are catalyzed by the sulfotransferases HS6ST-1, -2, and -3. To determine the biological and physiological importance of HS6ST-1, we now describe the creation of transgenic mice that lack this sulfotransferase. Most of our HS6ST-1-null mice died between embryonic day 15.5 and the perinatal stage, and those mice that survived were considerably smaller than their wild-type littermates. Some of these HS6ST-1-null mice exhibited development abnormalities, and histochemical and molecular analyses of these mice revealed an approximately 50% reduction in the number of fetal microvessels in the labyrinthine zone of the placenta relative to that in the wild-type mice. Because we observed a modest reduction in VEGF-A mRNA and protein in the tissues of HS6ST-1-null mice, an HS-dependent defect in cytokine signaling probably contributes to increased embryonic lethality and decreased growth. Biochemical studies of the HS chains isolated from various organs of our HS6ST-1-null mice revealed a marked reduction of GlcNAc(6SO(4)) and HexA-GlcNSO(3)(6SO(4)) levels and a reduced ability to bind Wnt2. Thus, despite the presence of three closely related 6-O-sulfotransferase genes in the mouse genome, HS6ST-1 is the primary one used in HS biosynthesis in most tissues.

Critical role for the p110alpha phosphoinositide-3-OH kinase in growth and metabolic regulation

The eight catalytic subunits of the mammalian phosphoinositide-3-OH kinase (PI(3)K) family form the backbone of an evolutionarily conserved signalling pathway; however, the roles of most PI(3)K isoforms in organismal physiology and disease are unknown. To delineate the role of p110alpha, a ubiquitously expressed PI(3)K involved in tyrosine kinase and Ras signalling, here we generated mice carrying a knockin mutation (D933A) that abrogates p110alpha kinase activity. Homozygosity for this kinase-dead p110alpha led to embryonic lethality. Mice heterozygous for this mutation were viable and fertile, but displayed severely blunted signalling via insulin-receptor substrate (IRS) proteins, key mediators of insulin, insulin-like growth factor-1 and leptin action. Defective responsiveness to these hormones led to reduced somatic growth, hyperinsulinaemia, glucose intolerance, hyperphagia and increased adiposity in mice heterozygous for the D933A mutation. This signalling function of p110alpha derives from its highly selective recruitment and activation to IRS signalling complexes compared to p110beta, the other broadly expressed PI(3)K isoform, which did not contribute to IRS-associated PI(3)K activity. p110alpha was the principal IRS-associated PI(3)K in cancer cell lines. These findings demonstrate a critical role for p110alpha in growth factor and metabolic signalling and also suggest an explanation for selective mutation or overexpression of p110alpha in a variety of cancers.

Role of phosphoinositide 3-kinase regulatory isoforms in development and actin rearrangement

Class Ia phosphoinositide 3-kinases (PI3Ks) are heterodimers of p110 catalytic and p85 regulatory subunits that mediate a variety of cellular responses to growth and differentiation factors. Although embryonic development is not impaired in mice lacking all isoforms of the p85alpha gene (p85alpha-/- p55alpha-/- p50alpha-/-) or in mice lacking the p85beta gene (p85beta-/-) (D. A. Fruman, F. Mauvais-Jarvis, D. A. Pollard, C. M. Yballe, D. Brazil, R. T. Bronson, C. R. Kahn, and L. C. Cantley, Nat Genet. 26:379-382, 2000; K. Ueki, C. M. Yballe, S. M. Brachmann, D. Vicent, J. M. Watt, C. R. Kahn, and L. C. Cantley, Proc. Natl. Acad. Sci. USA 99:419-424, 2002), we show here that loss of both genes results in lethality at embryonic day 12.5 (E12.5). The phenotypes of these embryos, including subepidermal blebs flanking the neural tube at E8 and bleeding into the blebs during the turning process, are similar to defects observed in platelet-derived growth factor receptor alpha null (PDGFRalpha-/-) mice (P. Soriano, Development 124:2691-2700, 1997), suggesting that PI3K is an essential mediator of PDGFRalpha signaling at this developmental stage. p85alpha-/- p55alpha+/+ p50alpha+/+ p85beta-/- mice had similar but less severe defects, indicating that p85alpha and p85beta have a critical and redundant function in development. Mouse embryo fibroblasts deficient in all p85alpha and p85beta gene products (p85alpha-/- p55alpha-/- p50alpha-/- p85beta-/-) are defective in PDGF-induced membrane ruffling. Overexpression of the Rac-specific GDP-GTP exchange factor Vav2 or reintroduction of p85alpha or p85beta rescues the membrane ruffling defect. Surprisingly, reintroduction of p50alpha also restored PDGF-dependent membrane ruffling. These results indicate that class Ia PI3K is critical for PDGF-dependent actin rearrangement but that the SH3 domain and the Rho/Rac/Cdc42-interacting domain of p85, which lacks p50alpha, are not required for this response.

Failure to degrade poly(ADP-ribose) causes increased sensitivity to cytotoxicity and early embryonic lethality

The metabolism of poly(ADP-ribose) (PAR) is critical for genomic stability in multicellular eukaryotes. Here, we show that the failure to degrade PAR by means of disruption of the murine poly(ADP-ribose) glycohydrolase (PARG) gene unexpectedly causes early embryonic lethality and enhanced sensitivity to genotoxic stress. This lethality results from the failure to hydrolyze PAR, because PARG null embryonic day (E) 3.5 blastocysts accumulate PAR and concurrently undergo apoptosis. Moreover, embryonic trophoblast stem cell lines established from early PARG null embryos are viable only when cultured in medium containing the poly(ADP-ribose) polymerase inhibitor benzamide. Cells lacking PARG also show reduced growth, accumulation of PAR, and increased sensitivity to cytotoxicity induced by N-methyl-N'-nitro-N-nitrosoguanidine and menadione after benzamide withdrawal. These results provide compelling evidence that the failure to degrade PAR has deleterious consequences. Further, they define a role for PARG in embryonic development and a protective role in the response to genotoxic stress.

Essential role for mitochondrial thioredoxin reductase in hematopoiesis, heart development, and heart function

Oxygen radicals regulate many physiological processes, such as signaling, proliferation, and apoptosis, and thus play a pivotal role in pathophysiology and disease development. There are at least two thioredoxin reductase/thioredoxin/peroxiredoxin systems participating in the cellular defense against oxygen radicals. At present, relatively little is known about the contribution of individual enzymes to the redox metabolism in different cell types. To begin to address this question, we generated and characterized mice lacking functional mitochondrial thioredoxin reductase (TrxR2). Ubiquitous Cre-mediated inactivation of TrxR2 is associated with embryonic death at embryonic day 13. TrxR2(TrxR2(-/-)minus;/TrxR2(-/-)minus;) embryos are smaller and severely anemic and show increased apoptosis in the liver. The size of hematopoietic colonies cultured ex vivo is dramatically reduced. TrxR2-deficient embryonic fibroblasts are highly sensitive to endogenous oxygen radicals when glutathione synthesis is inhibited. Besides the defect in hematopoiesis, the ventricular heart wall of TrxR2(TrxR2(-/-)minus;/TrxR2(-/-)minus;) embryos is thinned and proliferation of cardiomyocytes is decreased. Cardiac tissue-restricted ablation of TrxR2 results in fatal dilated cardiomyopathy, a condition reminiscent of that in Keshan disease and Friedreich's ataxia. We conclude that TrxR2 plays a pivotal role in both hematopoiesis and heart function.

[Influence of nitric oxide synthase inhibitors on embryonic destructions and morphological features in pre- and postimplantation mouse embryos]

Nitric oxide is an important intraovarian regulatory factor. The periimplantation period is a critical phase in mouse development. Although it was shown that nitric oxide plays an essential role during gestation, its role in the preimplantation period is not yet fully clear. We studied the involvement of nitric oxide in developmental competence (embryonic defects and morphology of pre- and postimplantation embryos) using nitric oxide synthase inhibitors, which suppress all forms of nitric oxide synthase, and female mice, to which the inhibitors had been administered before their mating with intact males. The level of mortality of pre- and postimplantation embryos in females mated to intact males increased soon after the administration of inhibitors. Studies of the morphology of embryos have shown that there was a delay in embryogenesis at the stages of cleavage and gastrulation. The results obtained suggest that nitric oxide is a potent regulator of embryonic differentiation, specifically in pre- and postimplantation mouse embryos.

Placental failure and impaired vasculogenesis result in embryonic lethality for neuropathy target esterase-deficient mice

Age-dependent neurodegeneration resulting from widespread apoptosis of neurons and glia characterize the Drosophila Swiss Cheese (SWS) mutant. Neuropathy target esterase (NTE), the vertebrate homologue of SWS, reacts with organophosphates which initiate a syndrome of axonal degeneration. NTE is expressed in neurons and a variety of nonneuronal cell types in adults and fetal mice. To investigate the physiological functions of NTE, we inactivated its gene by targeted mutagenesis in embryonic stem cells. Heterozygous NTE(+/-) mice displayed a 50% reduction in NTE activity but underwent normal organ development. Complete inactivation of the NTE gene resulted in embryonic lethality, which became evident after gastrulation at embryonic day 9 postcoitum (E9). As early as E7.5, mutant embryos revealed growth retardation which did not reflect impaired cell proliferation but rather resulted from failed placental development; as a consequence, massive apoptosis within the developing embryo preceded its resorption. Histological analysis indicated that NTE is essential for the formation of the labyrinth layer and survival and differentiation of secondary giant cells. Additionally, impairment of vasculogenesis in the yolk sacs and embryos of null mutant conceptuses suggested that NTE is also required for normal blood vessel development.

Effects of aminoguanidine and cyclooxygenase inhibitors on nitric oxide and prostaglandin production, and nitric oxide synthase and cyclooxygenase expression induced by lipopolysaccharide in the estrogenized rat uterus

BACKGROUND/OBJECTIVE

The aim of our study was first to investigate if there exists an interaction between nitric oxide (NO) and prostaglandin (PG) generation in the estrogenized rat uterus challenged by lipopolysaccharide (LPS), and, secondly, which isoforms of nitric oxide synthase (NOS) and cyclooxygenase (COX) participate in this process.

METHODS

To study the effect of LPS and to characterize the isoenzymes involved in the process, specific inhibitors of iNOS (aminoguanidine) and COX-II (meloxicam, nimesulide) and non-specific of COX (indomethacin) were injected intraperitoneally to determine their effect on NO and PG production, and on NOS and COX expression induced by LPS in estrogenized rat uterus. NO production was measured by arginine-citrulline conversion assay and PGE(2)/PGF(2alpha,)by radioconversion. Enzyme expression was evaluated by Western blot analysis.

RESULTS

The present work shows that iNOS inhibitor, aminoguanidine, reduced NO and PGE(2)/PGF(2alpha) production induced by LPS injection. Aminoguanidine exerts its effect over the PG metabolism by inhibiting COX-II activity and expression. On the other hand, both indomethacin, a non-selective PG inhibitor, and meloxicam, a COX-II inhibitor, stimulated NO production and reduced PGE(2)/PGF(2alpha) generation. Indomethacin also reduced COX-II and iNOS expression.

CONCLUSION

These results indicate that in the estrogenized rat uterus challenged with LPS, PG and NO interact affecting each other's metabolic pathways. The above findings indicate that the interaction between NOS and COX might be important in the regulation of physiopathologic events during pregnancy.

Inhibition of dipeptidyl peptidase IV (DP IV, CD26) activity abrogates stress-induced, cytokine-mediated murine abortions

In the CBA x DBA/2 mouse model, stress-triggered abortions are mediated by a Th1-like cytokine response of decidual lymphocytes. The factors that determine the cytokine pattern leading to abortion are currently unknown. Dipeptidyl Peptidase IV (DP IV) enhances Th1-cytokine responses and impairs the evolvement of a Th2 cytokine profile. The T-cell-activation antigen, CD26, possesses DP IV activity. The aim of the present study was to investigate the role of DP IV activity and CD26-positive decidual lymphocytes in murine stress-triggered abortions by inhibition of DP IV activity. DBA/2-mated CBA mice were stressed on day 5.5 of pregnancy and received daily injections of an inhibitor of DP IV activity, Ile-thiazolidide (20 micromol/kg). On day 13 of gestation, the animals were sacrificed and the percentage of implants and abortions documented. CD26-positive lymphocytes in spleen and uterine decidua and the intracellular cytokines interferon (IFN)-gamma and interleukin (IL)-10 were determined by flow cytometry. Stressed and nonstressed animals receiving an inactive stereoisomeric form were used as controls. In mice receiving the DP IV inhibitor, stress failed to boost the abortion rate (37.2% versus 13.6%, P < 0.01). IFN-gamma producing cells were increased in stressed animals, but returned to the baseline upon the inhibition of DP IV. The number of IL-10 producing cells was reduced in stressed animals, independent from DP IV inhibition.

Decreased UDP-GlcNAc levels abrogate proliferation control in EMeg32-deficient cells

The hexosamine pathway provides UDP-N:-acetylhexosamine donor substrates used in cytosolic and Golgi-mediated glycosylation of proteins and for formation of glycosylphosphatidylinositol (GPI) anchors, which tether proteins to the outer plasma membrane. We have recently identified the murine glucosamine-6-phosphate (GlcN6P) acetyltransferase, EMeg32, as a developmentally regulated enzyme on the route to UDP-N:-acetylglucosamine (UDP-GlcNAc). Here we describe embryos and cells that have the EMeg32 gene inactivated by homologous recombination. Homozygous mutant embryos die at around embryonic day (E) 7.5 with a general proliferative delay of development. In vitro differentiated EMeg32(-/-) ES cells show reduced proliferation. Mouse embryonic fibroblasts (MEFs) deficient for EMeg32 exhibit defects in proliferation and adhesiveness, which could be complemented by stable re-expression of EMeg32 or by nutritional restoration of intracellular UDP-GlcNAc levels. Reduced UDP-GlcNAc levels predominantly translated into decreased O-GlcNAc modifications of cytosolic and nuclear proteins. Interestingly, growth-impaired EMeg32(-/-) MEFs withstand a number of apoptotic stimuli and express activated PKB/AKT. Thus, EMeg32-dependent UDP-GlcNAc levels influence cell cycle progression and susceptibility to apoptotic stimuli.

[Lactate dehydrogenase activity of the ova and early embryos in BALB/c and C57BL/6 mice and their reciprocal hybrids]

The lactate dehydrogenase (LDH) activity in eggs and 8-cell mouse embryos of BALB/c, C57BL/6 strains and their reciprocal hybrids was studied. LDH pattern of mouse eggs and 8-cell embryos is represented by only one fast migrating isozyme LDH-1. For determining the water-soluble LDH activity water extraction of enzyme was used. For determining the total LDH activity triton X-100 extraction of enzyme was used. The bound LDH activity was estimated as a difference between total LDH and water-soluble LDH activities. The total LDH activity of eggs and 8-cell embryos for all genotypes is reliably higher than the water-soluble LDH activity. Differences between strains and hybrids are reliable. There is diversity of values of eggs and 8-cell embryos LDH activity. The diversity of values of water-soluble LDH activity is higher than that of the total LDH activity in all cases. The development from the egg to 8-cell embryo is accompanied by the decrease of the total LDH activity, the water-soluble LDH activity and the bound LDH activity for all genotypes except BALB/c. Only the water-soluble LDH activity decreases by BALB/c strain.

Termination of pregnancy after accelerated lactation in the rat. IV. Relationship to 20alpha-hydroxysteroid dehydrogenase activity and plasma progesterone concentration

The activity of 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) was assayed in the ovaries of rats after accelerated lactation to determine its relationship to the decrease in progesteron secretion that occurs. When rats were sjbjected to accelerated lactation on Day 9 of pregnancy, activity of the enzyme was only slightly increased by Day 10, but had risen to twice the control level by Day 11, and three times the control level by Day 12. Administration of LH or progesterone prevented the increase in enzyme activity. Progesterone concentration had decreased considerably before the time at which any significant increase in 20alpha-HSD activity was detected. These findings are discussed in relation to the role of 20alpha-HSF in regulating progesterone levels in the rat.