Genomic and Biochemical Characterization of Acinetobacter Podophage Petty Reveals a Novel Lysis Mechanism and Tail-Associated Depolymerase Activity.

The increased prevalence of drug-resistant, nosocomial Acinetobacter infections, particularly from pathogenic members of the Acinetobacter calcoaceticus-baumannii complex, necessitates the exploration of novel treatments such as phage therapy. In the present study, we characterized phage Petty, a novel podophage that infects multidrug-resistant Acinetobacter nosocomialis and Acinetobacter baumannii Genome analysis reveals that phage Petty is a 40,431-bp ϕKMV-like phage, with a coding density of 92.2% and a G+C content of 42.3%. Interestingly, the lysis cassette encodes a class I holin and a single-subunit endolysin, but it lacks canonical spanins to disrupt the outer membrane. Analysis of other ϕKMV-like genomes revealed that spaninless lysis cassettes are a feature of phages infecting Acinetobacter within this subfamily of bacteriophages. The observed halo surrounding Petty's large clear plaques indicated the presence of a phage-encoded depolymerase capable of degrading capsular exopolysaccharides (EPS). The product of gene 39, a putative tail fiber, was hypothesized to possess depolymerase activity based on weak homology to previously reported phage tail fibers. The 101.4-kDa protein gene product 39 (gp39) was cloned and expressed, and its activity against Acinetobacter EPS in solution was determined. The enzyme degraded purified EPS from its host strain A. nosocomialis AU0783, reducing its viscosity, and generated reducing ends in solution, indicative of hydrolase activity. Given that the accessibility to cells within a biofilm is enhanced by degradation of EPS, phages with depolymerases may have enhanced diagnostic and therapeutic potential against drug-resistant Acinetobacter strains.IMPORTANCE Bacteriophage therapy is being revisited as a treatment for difficult-to-treat infections. This is especially true for Acinetobacter infections, which are notorious for being resistant to antimicrobials. Thus, sufficient data need to be generated with regard to phages with therapeutic potential, if they are to be successfully employed clinically. In this report, we describe the isolation and characterization of phage Petty, a novel lytic podophage, and its depolymerase. To our knowledge, it is the first phage reported to be able to infect both A. baumannii and A. nosocomialis The lytic phage has potential as an alternative therapeutic agent, and the depolymerase could be used for modulating EPS both during infections and in biofilms on medical equipment, as well as for capsular typing. We also highlight the lack of predicted canonical spanins in the phage genome and confirm that, unlike the rounding of lambda lysogens lacking functional spanin genes, A. nosocomialis cells infected with phage Petty lyse by bursting. This suggests that phages like Petty employ a different mechanism to disrupt the outer membrane of Acinetobacter hosts during lysis.

Gender-specific changes in bone turnover and skeletal architecture in igfbp-2-null mice.

IGF-binding protein-2 (IGFBP-2) is a 36-kDa protein that binds to the IGFs with high affinity. To determine its role in bone turnover, we compared Igfbp2(-/-) mice with Igfbp2(+/+) colony controls. Igfbp2(-/-) males had shorter femurs and were heavier than controls but were not insulin resistant. Serum IGF-I levels in Igfbp2(-/-) mice were 10% higher than Igfbp2(+/+) controls at 8 wk of age; in males, this was accompanied by a 3-fold increase in hepatic Igfbp3 and Igfbp5 mRNA transcripts compared with Igfbp2(+/+) controls. The skeletal phenotype of the Igfbp2(-/-) mice was gender and compartment specific; Igfbp2(-/-) females had increased cortical thickness with a greater periosteal circumference compared with controls, whereas male Igfbp2(-/-) males had reduced cortical bone area and a 20% reduction in the trabecular bone volume fraction due to thinner trabeculae than Igfbp2(+/+) controls. Serum osteocalcin levels were reduced by nearly 40% in Igfbp2(-/-) males, and in vitro, both CFU-ALP(+) preosteoblasts, and tartrate-resistant acid phosphatase-positive osteoclasts were significantly less abundant than in Igfbp2(+/+) male mice. Histomorphometry confirmed fewer osteoblasts and osteoclasts per bone perimeter and reduced bone formation in the Igfbp2(-/-) males. Lysates from both osteoblasts and osteoclasts in the Igfbp2(-/-) males had phosphatase and tensin homolog (PTEN) levels that were significantly higher than Igfbp2(+/+) controls and were suppressed by addition of exogenous IGFBP-2. In summary, there are gender- and compartment-specific changes in Igfbp2(-/-) mice. IGFBP-2 may regulate bone turnover in both an IGF-I-dependent and -independent manner.

Perinatal hypoxia-ischemia induces apoptotic and excitotoxic death of periventricular white matter oligodendrocyte progenitors.

Hypoxia-ischemia (HI) is a leading cause of white matter damage, a major contributor to cerebral palsy in premature infants. Preferential white matter damage is believed to result from vulnerability of the immature oligodendrocyte (the pro-OL) to factors elevated during ischemic damage, such as oxygen free radicals and glutamate. In order to determine whether pro-OLs undergo apoptotic death after HI, we analyzed periventricular white matter OLs in P7 rats 4, 12 and 24 h after HI to analyze the time course and mode of cell death. DNA fragmentation was seen at 12 and 24 h of recovery after HI, representing a 17-fold increase over control. In addition, caspase-3 activation was found in NG2+ pro-OLs at 12 h. Electron-microscopic analysis of cell death in the white matter revealed a transition from early necrotic deaths to hybrid cell deaths to classical apoptosis between 4 and 24 h of recovery from HI. The delayed time course of apoptosis in pro-OLs supports the feasibility of interventions to improve clinical outcomes for newborns surviving birth asphyxia.

IGF-I synergizes with FGF-2 to stimulate oligodendrocyte progenitor entry into the cell cycle.

Secreted peptide growth factors are critical extracellular signals that interact to promote the proliferation, differentiation, and survival of progenitor cells in developing tissues. IGF-I signaling through the IGF type I receptor provides a mitogenic signal for numerous cell types, including stem and progenitor cells. We have utilized the O-2A oligodendrocyte progenitor to study the mechanism of IGF-I mitogenic actions since these progenitors respond to IGF-I in vitro, and gene targeting studies in mice have demonstrated that IGF-I is essential for normal oligodendrocyte development in vivo. The goal of this study was to elucidate the mechanism by which IGF-I promotes the proliferation of oligodendrocyte progenitors in the context of other mitogens critical for their proliferation. Results presented here show that IGF-I significantly amplified the actions of FGF-2 and PDGF to promote DNA synthesis in O-2A progenitors. Investigation of cell cycle kinetics revealed that IGF-I had no significant effect on the rate of cell cycle progression. Instead, IGF-I promoted increased recruitment of O-2A progenitors into the S phase of the cell cycle. These studies support a role for IGF-I as a cell cycle progression factor for progenitor cells.

Perceptions of an old female eyewitness: is the older eyewitness believable?

Young adults rated an old female witness (82 years) to be less competent but more honest than a young female witness (28 years). The effect of age stereotyping on believability was assessed indirectly by using a variant of Loftus' misinformation paradigm. Regression analysis showed that the more competent a witness was perceived as being, the more influential was the misinformation she provided. This was true, however, only when the witness was young because the relatively lower competence of the old witness was associated with nonsignificant misinformation effects. These data suggest that negative beliefs associating incompetence with old age may compromise the believability of older eyewitnesses.

Experimental stroke in the female diabetic, db/db, mouse.

Diabetic hyperglycemia increases brain damage after cerebral ischemia in animals and humans, although the underlying mechanisms remain unclear. Gender-linked differences in ischemic tolerance have been described but have not been studied in the context of diabetes. In the current study, we used a model of unilateral common carotid artery ligation, combined with systemic hypoxia, to study the effects of diabetes and gender on hypoxic-ischemic (HI) brain damage in the genetic model of Type II diabetes, the db/db, mouse. Male and female, control and db/db, mice were subjected to right common carotid artery ligation followed by varying periods of hypoxia (8% oxygen/92% nitrogen) to assess mortality, infarct volume, and tissue damage by light microscopic techniques. End-ischemic regional cerebral blood flow (CBF) was determined using [14C] iodoantipyrine autoradiography. Glycolytic and high energy phosphate compounds were measured in blood and brain by enzymatic and fluorometric techniques. Gender and diabetes had significant effects on mortality from HI and extent of brain damage in the survivors. Female mice were more resistant than their male counterparts, such that the severity (mortality and infarction size) in the male diabetics > female diabetics - male controls > female controls. Endischemic CBF and depletion of cerebral high energy reserves were comparable among all groups. Surprisingly, female diabetic mice were more hyperglycemic and demonstrated a greater prolonged lactacidosis than the males; however, they were more resistant to damage. The results suggest a unique pathophysiology of hypoxia-ischemia in the female diabetic brain.

Selective alterations in organ sizes in mice with a targeted disruption of the insulin-like growth factor binding protein-2 gene.

Insulin-like growth factor binding protein 2 (IGFBP-2) is one member of the family of IGF binding proteins believed to have both endocrine functions elicited by modulating serum IGF half-life and transport as well as autocrine/paracrine functions that result from blocking or enhancing the availability of IGFs to bind cell surface receptors. To clarify the in vivo role of IGFBP-2, we have used gene targeting to introduce a null IGFBP-2 allele into the mouse genome. Animals homozygous for the altered allele are viable and fertile, contain no IGFBP-2 mRNA, and have no detectable IGFBP-2 in the adult circulation. Heterozygous and homozygous animals showed no significant differences in prenatal or postnatal body growth. Analyses of organ weights in adult males, however, revealed that spleen weight was reduced and liver weight was increased in the absence of IGFBP-2. In addition, ligand blot analyses of sera from adult IGFBP-2 null males showed that IGFBP-1, IGFBP-3, and IGFBP-4 levels were increased relative to wild-type mice. These results demonstrate that up-regulation of multiple IGFBPs accompanies the absence of IGFBP-2 and that IGFBP-2 has a critical role, either directly or indirectly, in modulating spleen and liver size.

The insulin-like growth factors (IGFs) and IGF binding proteins in postnatal development of murine mammary glands.

The insulin-like growth factors are mitogens and survival factors for normal mammary epithelial cells in vitro. Data reviewed here demonstrate that mRNAs for IGF-I and IGF-II, the IGF type I receptor and the IGFBPs are expressed locally in mammary tissue during pubertal and pregnancy-induced growth and differentiation of murine mammary glands. IGF-I, IGF-II and the IGF-IR were expressed in terminal end buds (TEBs) in virgin glands during ductal growth. In addition, IGF-II and IGF-IR mRNAs were expressed in ductal and alveolar epithelium in glands throughout postnatal development. Consistent with these results, IGF-I promoted ductal growth and proliferation in mouse mammary glands in organ culture. In addition to endogenous expression of the IGFs and IGF-IR, the IGFBPs showed a varied pattern of expression in mammary tissue during postnatal development. For example, IGFBP-3 and -5 mRNAs were expressed in TEBs and ducts while IGFBP-2 and -4 mRNAs were expressed in stromal cells immediately surrounding the epithelium. These results support a role for the IGFs and IGFBPs as local mediators of postnatal mammary gland growth and differentiation.

Ciliary neurotrophic factor induces expression of the IGF type I receptor and FGF receptor 1 mRNAs in adult rat brain oligodendrocytes.

Ciliary neurotrophic factor (CNTF) is produced and released in response to injury in the central nervous system (CNS). While CNTF initially was characterized as a trophic factor for neurons, more recent evidence supports roles for this factor in survival, proliferation, and maturation of oligodendrocyte lineage cells. Evidence is emerging to support the hypothesis that CNTF's actions may include enhancing other growth and trophic factors. Here we tested the hypothesis that CNTF can induce expression of receptors on oligodendrocytes for factors that are known to promote their generation, maturation, and survival. Specifically, we used an in vivo paradigm to test whether CNTF, when injected stereotactically into forebrain white matter of adult rats, could induce mRNA expression for the insulin-like growth factor (IGF) type I receptor (IGF-IR), fibroblast growth factor (FGF) receptor (FGFR)-1, FGFR3, and platelet-derived growth factor (PDGF) receptor-alpha (PDGFRalpha). We determined that CNTF injection increased expression of IGF-IR and FGFR1 mRNAs in adult white matter to 200-250% of control levels. Cellular analysis indicated that these receptor mRNAs were induced in interfascicular oligodendrocytes. In contrast, CNTF had no effect on levels of FGFR3 and PDGFRalpha mRNAs. These results suggest that CNTF enhances the sensitivity of oligodendrocytes to other mitogens and trophic factors via induction of their receptors.

The insulin-like growth factors (IGF) and IGF type I receptor during postnatal growth of the murine mammary gland: sites of messenger ribonucleic acid expression and potential functions.

The goals of this study were to determine the cellular sites of insulin-like growth factor (IGF) and IGF type-I receptor (IGF-IR) expression and to begin to elucidate functional roles for the IGFs during postnatal development of the murine mammary gland. Using in situ hybridization analyses, we determined that IGF-I, IGF-II, and IGF-IR messenger RNAs were expressed in the highly proliferative terminal end buds during pubertal ductal growth. Consistent with these data, IGF-I (in combination with mammogenic hormones) promoted ductal growth in pubertal stage mammary glands cultured in vitro. During postpubertal and pregnancy stages, IGF-II and IGF-IR continued to be expressed in ductal epithelium. Expression of IGF-II in ductal and alveolar epithelium correlated with the pattern of rapidly proliferating cells, as determined by incorporation of 5-Bromo-2'-deoxyuridine, suggesting a potential autocrine or paracrine role for IGF-II as a mitogen for ductal epithelial cells. IGF-I expression was reinitiated in mammary epithelium in the differentiated alveoli at the end of pregnancy, suggesting an additional role for this factor in maintenance of the alveoli during lactation. Taken together, these data support an in vivo role for locally-produced IGFs in promoting ductal growth during puberty and suggest that IGF-I and IGF-II may have distinct functions during pregnancy-induced alveolar development.

Expression of mouse ovarian insulin growth factor system components during follicular development and atresia.

Insulin growth factor I (IGF-I) appears necessary for the completion of follicular development in mice. However, little is known about changes in the IGF system components during follicular development and luteinization. This study determined the relation between gene expression of specific IGF system components and follicular growth, survival, or atresia in mice. Immature mice from three different strains (129, C57, and MF1), with or without gonadotropin treatment (2.5 IU PMSG/2.5 IU human CG (hCG)], were used. The strains were similar in all parameters measured. Apoptosis, as detected by in situ labeling of nicked DNA, preceded the appearance of morphological signs of atresia. In healthy follicles, IGF-I transcripts were low during the primary follicular stage but increased to a maximum in the late preantral and early antral stages (P < 0.001) irrespective of hormone treatment. Occasionally, IGF-I transcripts were also detected in apoptotic follicles but decreased (P < 0.05) as a function of atresia as assessed by morphological criteria. IGF binding protein-4 (IGFBP-4) messenger RNA (mRNA) expression in granulosa cells was restricted to apoptotic and atretic follicles (P < 0.001). IGFBP-5 transcript levels, on the other hand, were elevated in granulosa cells of healthy primary and secondary follicles but decreased in subsequent follicular stages and in atretic follicles (P < 0.001). Conversely, IGFBP-2 mRNA was constitutively expressed in granulosa cells. PMSG/hCG treatment induced the appearance of IGFBP-2 transcripts in the ovarian interstitium. Following PMSG/hCG-induced ovulation, IGFBP-2 and -4 and IGF type-I receptor mRNAs were strongly expressed in virtually all luteal cells, whereas IGFBP-3 and -5 transcripts were selectively localized to some cell types in the corpus luteum. Conversely, IGF-I mRNA was essentially undetectable in the corpus luteum. This study represents the most comprehensive and detailed analysis of the physiology and anatomy of the mouse ovarian IGF system, and shows that 1) IGFBP-5-is linked to the survival of the slow growing and immature preantral follicles; 2) IGF-I is associated with the growth and survival of the rapidly growing large preantral and antral follicles; 3) IGFBP-4 is an atretogenic candidate for mouse ovarian follicles; 4) ovulatory doses of PMSG/hCG up-regulate IGFBP-2 mRNA expression in the ovarian interstitium; and 5) transcripts of IGF type-I receptor and IGFBP-2 through -5, but not those of IGF-I are highly expressed in the mouse corpus luteum.

Stimulation of tumor growth by recombinant human insulin-like growth factor-I (IGF-I) is dependent on the dose and the level of IGF-I receptor expression.

The insulin-like growth factors (IGF) I and II regulate metabolism, mitogenesis, differentiation, and apoptosis. The therapeutic uses of IGF-I have been discussed extensively; however, excessive activity of the IGF ligands and IGF-I receptor has been suggested as a factor in tumorigenesis. The inhibition of apoptosis by IGF-I is believed to be particularly important for the stimulation of tumor growth. This study examined whether systemic recombinant human IGF-I (rhIGF-I) therapy affects the growth of fibrosarcomas derived from fibroblasts expressing the IGF-I receptor at high or naturally occurring densities (1.9 x 10(5) compared with 1.6 x 10(4) IGF-I receptors/cell) in athymic nude mice. Treatment with 4 or 10 mg/kg rhIGF-I resulted in a marked reduction in the tumor latency and stimulated the growth of fibrosarcomas that overexpressed the IGF-I receptor. The latency and growth of fibrosarcomas expressing parental levels of the IGF-I receptor were not affected by rhIGF-I therapy. Analysis of mitosis by histone H3 mRNA in situ hybridization and of apoptosis by terminal deoxynucleotidyl transferase-mediated nick end labeling assay indicated that rhIGF-I-stimulated tumor growth was associated with a marked increase in mitogenesis; however, there was no evidence for any significant effect on apoptosis. These data imply that: (a) systemic rhIGF-I can stimulate the growth of tumors directly by stimulating mitosis; and (b) a reasonable level of IGF-I receptor expression is required for stimulation of tumor growth by systemic rhIGF-I.

Developmental and tissue-specific sulfonylurea receptor gene expression.

We have studied the developmental regulation of mouse sulfonylurea receptor (SUR) gene expression throughout several embryonic stages as well as in the adult mouse. To this end we used a 229-bp mouse complementary DNA corresponding to the 3'-end of the SUR gene for in situ hybridization and solution hybridization/ribonuclease protection assays. We found that the SUR gene was expressed as early as embryonic day 12 in the developing pancreas, heart, and central nervous system. These tissues maintained significant levels of SUR messenger RNA (mRNA) throughout development. In addition, SUR mRNA was detected in the submandibular gland, anterior duodenum, dorsal root ganglia, lens, retina, and vibrissae by late developmental stages. SUR mRNA is widely distributed in adult mouse tissues, with the exception of the liver. In the adult pancreas, the SUR gene was expressed exclusively in endocrine tissue. Although significant levels of SUR mRNA were broadly seen throughout the brain, neurons of the cerebellum, hippocampus, and thalamus had especially high levels of SUR mRNA. These findings support the idea that the SUR has important functions in many other tissues in addition to the islets of the pancreas.

Acute exposure to CNTF in vivo induces multiple components of reactive gliosis.

CNS trauma or disease induces a constellation of changes in the glia comprising the condition known as reactive gliosis. At present, little is known regarding the nature of the injury signals and the specific consequences of their actions. Ciliary neurotrophic factor (CNTF) induces acute phase proteins in liver and increases astrocytic glial fibrillary acidic protein (GFAP) both in vitro and in vivo. The purpose of the present study was to establish whether CNTF induces other aspects of gliosis. Between 10 and 72 h after 100 ng of recombinant human CNTF was administered into the adult rat neocortex, alterations were observed in a region extending several millimeters in circumference from the injection site. Microglia in this region were more apparent and astrocytes were hypertrophic. By in situ hybridization, mRNAs for GFAP, vimentin, and clusterin were upregulated when compared to the control hemisphere (which received heat-inactivated CNTF). By immunocytochemistry, GFAP, vimentin, glutathione-S-transferase mu, S-100, and OX-42 were elevated by 48 h. By contrast, the oligodendroglial marker GSTYp, the neuronal markers MAP-2 and NSE, the intermediate filament nestin, and the stress protein alpha B-crystallin were unchanged. In addition, a greater than twofold increase in the number of proliferating cells was observed. Since CNTF induces swelling and multiple "gliotic" genes in astrocytes, increases microglial number, and stimulates cell proliferation, we conclude that CNTF is sufficient to induce multiple aspects of gliosis. These data are consistent with a model whereby CNTF (which is synthesized by astrocytes) would be released when the integrity of the astrocyte membrane is compromised, whereupon it would elicit an inflammatory response.

Involution of the lactating mammary gland is inhibited by the IGF system in a transgenic mouse model.

Development of the mammary gland during puberty, pregnancy, and lactation is controlled by steroid and peptide hormones and growth factors. To determine the role of the insulin-like growth factors (IGFs) in this process we developed a transgenic model using the whey acidic protein (WAP) gene to direct expression of rat IGF-I and human IGF binding protein-3 (IGFBP-3) to mammary tissue during late pregnancy and throughout lactation. High levels of expression of transgenic IGF-I and IGFBP-3 were seen in lobular-alveolar cells by in situ hybridization. There was no obvious effect on mammary development during pregnancy and lactation; indeed, mothers were capable of nursing their pups normally and the only structural difference seen in the mammary glands at peak lactation was an overall smaller size of the alveoli. We also evaluated the role of IGF-I and IGFBP-3 in the remodeling of mammary tissue during involution. Compared with control animals, the process of involution was modified in both transgenic lines. The degree of apoptotic cells was lower in the WAP-IGF-I and WAP-BP-3 expressing mice. In addition, there was a more quiescent pattern of involution with residual lobular secretary ability and a muted host inflammatory reaction with fewer lumenal microcalcifications. These results demonstrate that IGF-I and IGFBP-3 may modulate the involutionary process of the lactating mammary gland.

Genetic approaches to the function of insulin-like growth factor-binding proteins during rodent development.

Gene targeting provides a direct method for introducing mutations into specific mouse loci. This approach has been used productively to demonstrate that insulin-like growth factor (IGF) peptides and receptors are required for normal prenatal growth. Six genes comprising a third major component of the IGF system, the IGF-binding proteins (IGFBPs), are all expressed during prenatal rodent development. One of these genes, IGFBP-2, has also been disrupted using gene targeting, and homozygous null BP-2 mice are characterized by a decreased spleen size and an increase in circulating levels of other IGFBPs. These alterations are less dramatic than initially expected based on the fetal IGFBP-2 expression pattern. These results are discussed in light of both other genetic ablations involving members of gene families and in the context of the expression of other IGFBPs in rodent fetal and uterine tissues.

Gene-targeting and transgenic approaches to IGF and IGF binding protein function.

The ability to manipulate genetic information in the germ line of mice has provided powerful approaches to study gene function in vivo. These approaches have included the establishment of mouse lines in which a specified gene or genes are overexpressed, ectopically expressed, or deleted. Transgenic and gene-targeted mouse lines have been used extensively to study the function of the insulin-like growth factors (IGF), IGF-I and IGF-II, and their receptors and binding proteins. In the IGF system, these technologies have elucidated the roles of the IGFs in fetal and somatic growth and have demonstrated a critical role for this system in transformation and tumorigenesis. Analysis of combinatorial crosses of gene-targeted mouse lines also has suggested the existence of an as yet unidentified IGF receptor that regulates fetal growth. Similar approaches using transgenic and gene-targeted mouse models have been initiated to study the in vivo functions of the IGF binding proteins. These mouse models provide important tools to test specific functional questions in vivo as well as to study the long-term physiological consequences of chronic gene alterations.

Cytokines regulate IGF binding proteins in the cns.

Growth factor induction is a major component of the response to central nervous system trauma. The insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) are among the molecules induced by injury that have demonstrated neuroprotective actions. Induction of IGFBPs 2, 3, 4 and 5 have been documented following injury and are hypothesized to function in transport or localization of the IGFs to injured cells. It is unclear what factors lead to induction of these molecules following trauma, however, several cytokines including ciliary neurotrophic factor (CNTF) and interleukin-1 beta (IL-1 beta) have been described as major injury signals and can induce aspects of reactive gliosis. To establish whether these cytokines also are responsible for inducing the IGFBPs following CNS injury, we injected CNTF or IL-1 beta intracerebrally into the neocortex of adult rats and measured changes in mRNA expression for the IGFBPs. IGFBP-2 mRNA showed a dramatic increase by 24-48 h following either CNTF or IL-1 beta injection as compared with the contralateral side injected with heat-inactivated cytokine. Neither CNTF nor IL-1 beta caused alterations in BP3 or BP5. Levels of BP4 and BP6 mRNAs also were unchanged following CNTF injection. These results suggest that IGFBP2 is uniquely regulated among the IGFBPs in the CNS and is induced by cytokines that signal CNS injury.

Insulin-like growth factor-I and insulin-like growth factor binding protein-3 inhibit involution of the mammary gland following lactation: studies in transgenic mice.

The role of the insulin-like growth factor system on mammary gland development and involution following pregnancy and lactation was studied. Transgenic mice expressing rat IGF-I and human IGFBP-3 specifically in the mammary gland tissue, were created using the whey acidic protein gene. Mammary gland development was normal in transgenic animals expressing either rIGF-I or hIGFBP-3. In contrast, involution of the gland was delayed in both groups of transgenic mice. Specifically, the number of apoptotic cells was less in the involuting glands of transgenic mice compared with control animals. These results confirm the hypothesis that the IGF system regulates mammary gland function.