A CamKIIalpha iCre BAC allows brain-specific gene inactivation

We describe the generation of transgenic mouse lines expressing the Cre recombinase enzyme in brain under control of the CamKIIalpha gene present in a BAC expression vector. The CamKIIalpha BAC transgene gave a faithful expression pattern resembling the pattern of the endogenous CamKIIalpha gene. Specifically, high levels of CamKIIalpha Cre were detected in hippocampus, cortex, and amygdala, and lower levels were detected in striatum, thalamus, and hypothalamus. As expected, no expression was detected in the cerebellum or outside of the brain. The expression level of the BAC CamKIIalpha driven Cre was shown to be copy number dependent. To test the activity of the Cre recombinase, the transgenic mice were crossed with mice harbouring the CREB (cAMP response element binding protein) allele with the 10th exon flanked by two loxP sites, and recombination was monitored by the disappearance of the CREB protein. Finally, evaluation of the developmental postnatal expression of the CamKIIalpha Cre BAC revealed the expression of the Cre recombinase as early as P3.

The C-terminal region of PTHrP, in addition to the nuclear localization signal, is essential for the intracrine stimulation of proliferation in vascular smooth muscle cells

PTHrP is secreted by most cell types. In addition to a paracrine/autocrine role, PTHrP has "intracrine" actions, entering the nuclear compartment under the direction of a classic bipartite nuclear localization signal. In vascular smooth muscle cells, nuclear entry stimulates mitogenesis. In the current study, we sought to more precisely define the regions of PTHrP required for the activation of mitogenesis in vascular smooth muscle cells. PTHrP deletion mutants missing large regions [i.e. the signal peptide, N terminus (1--36), mid region (38--86), nuclear localization signal, C terminus (108--139), or combinations of the above] were expressed in A-10 vascular smooth muscle cells. The consequences on nuclear localization and proliferation were examined. Deletion of the nuclear localization signal prevented nuclear entry and slowed proliferation. Deletion of the highly conserved N terminus or mid region had no impact on nuclear localization or on proliferation. Deletion of the C terminus had no deleterious effect on nuclear localization but dramatically reduced proliferation. Thus, the nuclear localization signal is both necessary and sufficient for nuclear localization of PTHrP. In contrast, activation of proliferation in vascular smooth muscle cells requires both an intact nuclear localization signal and an intact C terminus. Whereas the nuclear localization signal is required for nuclear entry, the C terminus may serve a trans-activating function to stimulate mitogenesis once inside the nucleus of vascular smooth muscle cells.

NSD3, a new SET domain-containing gene, maps to 8p12 and is amplified in human breast cancer cell lines

We describe the isolation and characterization of NSD3, the third member of a gene family including Nsd1 and NSD2. Murine Nsd1 was isolated in a search for proteins that interact with the ligand-binding domain of retinoic acid receptor alpha. NSD2 (also known as WHSC1 and MMSET) is located in the Wolf-Hirschhorn syndrome (WHS) critical region on 4p16.3 and is involved in multiple myeloma with t(4;14) translocations. The proteins Nsd1, NSD2, and NSD3 are highly similar within a block of about 700 amino acids. This block contains several conserved domains, such as the SET domain and the PHD finger, present in proteins involved in development and/or chromatin reorganization. The NSD3 gene consists of an 8.5-kb transcript composed of 23 coding exons and spans >90 kb of genomic DNA. NSD3 maps to chromosome band 8p12 and is amplified in several tumor cell lines and primary breast carcinomas.

Techniques: Recombinogenic engineering--new options for cloning and manipulating DNA

Driven by the needs of functional genomics, DNA engineering by homologous recombination in Escherichia coli has emerged as a major addition to existing technologies. Two alternative approaches, RecA-dependent engineering and ET recombination, allow a wide variety of DNA modifications, including some which are virtually impossible by conventional methods. These approaches do not rely on the presence of suitable restriction sites and can be used to insert, delete or substitute DNA sequences at any desired position on a target molecule. Furthermore, ET recombination can be used for direct subcloning and cloning of DNA sequences from complex mixtures, including bacterial artificial chromosomes and genomic DNA preparations. The strategies reviewed in this article are applicable to modification of DNA molecules of any size, including very large ones, and present powerful new avenues for DNA manipulation in general.

Parathyroid hormone-related protein-(1--36) stimulates renal tubular calcium reabsorption in normal human volunteers: implications for the pathogenesis of humoral hypercalcemia of malignancy

All would agree that hypercalcemia occurs among patients with humoral hypercalcemia of malignancy (HHM) as a result of osteoclastic bone resorption. Some studies suggest that enhanced renal calcium reabsorption, which plays an important pathophysiological role in the hypercalcemia occurring in primary hyperparathyroidism, is also important pathophysiologically in HHM. Other studies have not agreed. In large part, these differences result from the inability to accurately assess creatinine and calcium clearance in critically ill subjects with HHM. To circumvent these issues, we have developed steady state 48-h PTH-related protein (PTHrP) infusion and 8-h hypercalcemic calcium clamp protocols. These techniques allow assessment of the effects of steady state PTHrP and calcium infusions in normal healthy volunteers in a setting in which renal function is stable and measurable and in which the filtered load of calcium can be matched in PTHrP- and calcium-infused subjects. Normal subjects were infused with saline (placebo), PTHrP, or calcium. Subjects receiving PTHrP, as expected, displayed mild hypercalcemia (10.2 mg/dL), suppression of endogenous PTH-(1--84), and phosphaturia. Subjects receiving the hypercalcemic calcium clamp displayed indistinguishable degrees of hypercalcemia and PTH suppression. Despite their matched degrees of hypercalcemia and PTH suppression, the two groups differed importantly with regard to fractional calcium excretion (FECa). The hypercalcemic calcium clamp group was markedly hypercalciuric (FECa averaged 6.5%), whereas FECa in the PTHrP-infused subjects was approximately 50% lower (between 2.5--3.7%), and no different from that in the normal controls, which ranged from 1.5--3.0%. These studies demonstrate that PTHrP is able to stimulate renal calcium reabsorption in healthy volunteers. These studies suggest that PTHrP-induced renal calcium reabsorption, in concert with the well established acceleration of osteoclastic bone resorption, contributes in a significant way to the hypercalcemia observed in patients with HHM.

Independent regulation of cardiac Kv4.3 potassium channel expression by angiotensin II and phenylephrine

Hypertrophied cardiac myocytes exhibit prolonged action potentials and decreased transient outward potassium current (I(to)). Because Kv4.3 is a major contributor to I:(to), we studied regulation of its expression in neonatal rat cardiac myocytes in response to the known stimulators of cardiac myocyte hypertrophy, angiotensin II (Ang II) and phenylephrine (PE). RNase protection assays and immunoblots revealed that Ang II and PE each downregulate Kv4.3 mRNA and protein. However, although PE induces a faster and more extensive hypertrophic response than Ang II, the PE effect on Kv4.3 mRNA develops slowly and is sustained, whereas Ang II rapidly and transiently decreases Kv4.3 mRNA expression. Turnover measurements revealed that Kv4.3 mRNA is very stable, with a half-life >20 hours. This suggests that Ang II must destabilize the channel mRNA. In contrast, PE does not affect the rate of Kv4.3 mRNA degradation. To test for transcriptional regulation, the 5' flanking region of the rat Kv4.3 gene was cloned, and Kv4.3 promoter-reporter constructs were expressed in cardiac myocytes. Whereas Ang II was found to have no effect on transcription, PE inhibits Kv4.3 promoter activity. Pharmacological experiments also indicate that PE and Ang II act independently to downregulate Kv4.3 gene expression. Thus, regulation of Kv4.3 gene expression is not a simple secondary response to hypertrophy. Rather, Ang II and PE use different mechanisms to decrease Kv4.3 channel expression in neonatal rat cardiac myocytes.

Using beta-cell growth factors to enhance human pancreatic Islet transplantation

This is a particularly exciting time in the field of pancreatic islet growth, development, and survival. The recent publication of a study demonstrating that human pancreatic islet transplantation is both technically and immunologically feasible has highlighted the need for large supplies of pancreatic islets or pancreatic beta cells for larger-scale islet transplantation in patients with diabetes. This, together with a rapid expansion in the past several years of the understanding of mechanisms of islet growth, development, and survival, has accelerated and invigorated efforts to therapeutically harness the cellular mechanisms responsible for pancreatic beta-cell proliferation, survival, and development and to take advantage of this new knowledge to enhance the availability, survival, and function of pancreatic beta cells in human islet transplantation for diabetes mellitus. Here, we briefly review the confluence of events that have provided optimism and energy to the islet transplant field, and we focus on peptide growth factors that eventually may be deployed in the effort to augment islet mass and function in patients with diabetes.

DNA cloning by homologous recombination in Escherichia coli

The cloning of foreign DNA in Escherichia coli episomes is a cornerstone of molecular biology. The pioneering work in the early 1970s, using DNA ligases to paste DNA into episomal vectors, is still the most widely used approach. Here we describe a different principle, using ET recombination, for directed cloning and subcloning, which offers a variety of advantages. Most prominently, a chosen DNA region can be cloned from a complex mixture without prior isolation. Hence cloning by ET recombination resembles PCR in that both involve the amplification of a DNA region between two chosen points. We apply the strategy to subclone chosen DNA regions from several target molecules resident in E. coli hosts, and to clone chosen DNA regions from genomic DNA preparations. Here we analyze basic aspects of the approach and present several examples that illustrate its simplicity, flexibility, and remarkable efficiency.

Point mutation of bacterial artificial chromosomes by ET recombination

Bacterial artificial chromosomes (BACs) offer many advantages for functional studies of large eukaryotic genes. To utilize the potential applications of BACs optimally, new approaches that allow rapid and precise engineering of these large molecules are required. Here, we describe a simple and flexible two-step approach based on ET recombination, which permits point mutations to be introduced into BACs without leaving any other residual change in the recombinant product. Introduction of other modifications, such as small insertions or deletions, is equally feasible. The use of ET recombination to achieve site-directed mutagenesis opens access to a powerful use of BACs and is extensible to DNA molecules of any size in Escherichia coli, including the E. coli chromosome.

RecE/RecT and Redalpha/Redbeta initiate double-stranded break repair by specifically interacting with their respective partners

The initial steps of double-stranded break (DSB) repair by homologous recombination mediated by the 5'-3' exonuclease/annealing protein pairs, RecE/RecT and Redalpha/Redbeta, were analyzed. Recombination was RecA-independent and required the expression of both components of an orthologous pair, even when the need for exonuclease activity was removed by use of preresected substrates. The required orthologous function correlated with a specific protein-protein interaction, and recombination was favored by overexpression of the annealing protein with respect to the exonuclease. The need for both components of an orthologous pair was observed regardless of whether recombination proceeded via a single-strand annealing or a putative strand invasion mechanism. The DSB repair reactions studied here are reminiscent of the RecBCD/RecA reaction and suggest a general mechanism that is likely to be relevant to other systems, including RAD52 mediated recombination.

RecE/RecT and Redα/Redβ initiate double-stranded break repair by specifically interacting with their respective partners

The initial steps of double-stranded break (DSB) repair by homologous recombination mediated by the 5′–3′ exonuclease/annealing protein pairs, RecE/RecT and Redα/Redβ, were analyzed. Recombination was RecA-independent and required the expression of both components of an orthologous pair, even when the need for exonuclease activity was removed by use of preresected substrates. The required orthologous function correlated with a specific protein–protein interaction, and recombination was favored by overexpression of the annealing protein with respect to the exonuclease. The need for both components of an orthologous pair was observed regardless of whether recombination proceeded via a single-strand annealing or a putative strand invasion mechanism. The DSB repair reactions studied here are reminiscent of the RecBCD/RecA reaction and suggest a general mechanism that is likely to be relevant to other systems, including RAD52 mediated recombination.

Six-month daily administration of parathyroid hormone and parathyroid hormone-related protein peptides to adult ovariectomized rats markedly enhances bone mass and biomechanical properties: a comparison of human parathyroid hormone 1-34, parathyroid hormone-related protein 1-36, and SDZ-parathyroid hormone 893

Daily administration of parathyroid hormone (PTH) and PTH-related protein (PTHrP) peptides has been shown to increase bone mass and strength in animals and, for PTH, to increase bone mass in humans. Long-term direct comparison of multiple members of the PTH/PTHrP family in vivo has not been reported. We therefore selected three PTH/PTHrP molecules for direct comparison in vivo in an adult rat model of postmenopausal osteoporosis: PTH(1-34), PTHrP(1-36), and the PTH analog, SDZ-PTH 893 ¿Leu8, Asp10, Lys11, Ala16, Gln18, Thr33, Ala34 human PTH 1-34 [hPTH(1-34)]¿. A 6-month study was performed in which adult (6-month-old) vehicle-treated ovariectomized (OVX) and sham OVX rats were compared with OVX rats receiving 40 micrograms/kg per day of either PTH(1-34), PTHrP(1-36), or PTH-SDZ-893. Bone mass, as assessed by ash weight and densitometry, bone histomorphometry, biomechanical properties at trabecular and cortical sites, and indices of bone formation markedly increased in all three PTH/PTHrP peptide-treated groups as compared with controls. In general, this improvement followed a rank order of SDZ-PTH-893 > PTH > PTHrP. The adverse effect profile also was greatest with SDZ-PTH-893; these rats developed moderate hypercalcemia, marked renal calcium accumulation, and displayed a 13% mortality. These studies show that PTH(1-34), PTHrP(1-36), and PTH-SDZ-893 significantly and progressively increase bone mass and bone strength in this rat model of postmenopausal osteoporosis. The adverse effect profile correlates in general terms with efficacy. All three peptides show promise as skeletal anabolic agents. Further studies in humans will be required to define optimal efficacy-to-adverse effect ratios and relative efficacy for each peptide in human osteoporosis.

Identification of the functional domain in the transcription factor RTEF-1 that mediates alpha 1-adrenergic signaling in hypertrophied cardiac myocytes

Cardiac myocytes respond to alpha(1)-adrenergic receptor stimulation by a progressive hypertrophy accompanied by the activation of many fetal genes, including skeletal muscle alpha-actin. The skeletal muscle alpha-actin gene is activated by signaling through an MCAT element, the binding site of the transcription enhancer factor-1 (TEF-1) family of transcription factors. Previously, we showed that overexpression of the TEF-1-related factor (RTEF-1) increased the alpha(1)-adrenergic response of the skeletal muscle alpha-actin promoter, whereas TEF-1 overexpression did not. Here, we identified the functional domains and specific sequences in RTEF-1 that mediate the alpha(1)-adrenergic response. Chimeric TEF-1 and RTEF-1 expression constructs localized the region responsible for the alpha(1)-adrenergic response to the carboxyl-terminal domain of RTEF-1. Site-directed mutagenesis was used to inactivate eight serine residues of RTEF-1, not present in TEF-1, that are putative targets of alpha(1)-adrenergic-dependent kinases. Mutation of a single serine residue, Ser-322, reduced the alpha(1)-adrenergic activation of RTEF-1 by 70% without affecting protein stability, suggesting that phosphorylation at this serine residue accounts for most of the alpha(1)-adrenergic response. Thus, these results demonstrate that RTEF-1 is a direct target of alpha(1)-adrenergic signaling in hypertrophied cardiac myocytes.

Targeted expression of placental lactogen in the beta cells of transgenic mice results in beta cell proliferation, islet mass augmentation, and hypoglycemia

The factors that regulate pancreatic beta cell proliferation are not well defined. In order to explore the role of murine placental lactogen (PL)-I (mPL-I) in islet mass regulation in vivo, we developed transgenic mice in which mPL-I is targeted to the beta cell using the rat insulin II promoter. Rat insulin II-mPL-I mice displayed both fasting and postprandial hypoglycemia (71 and 105 mg/dl, respectively) as compared with normal mice (92 and 129 mg/dl; p < 0.00005 for both). Plasma insulin concentrations were inappropriately elevated, and insulin content in the pancreas was increased 2-fold. Glucose-stimulated insulin secretion by perifused islets was indistinguishable from controls at 7.5, 15, and 20 mm glucose. Beta cell proliferation rates were twice normal (p = 0. 0005). This hyperplasia, together with a 20% increase in beta cell size, resulted in a 2-fold increase in islet mass (p = 0.0005) and a 1.45-fold increase in islet number (p = 0.0012). In mice, murine PL-I is a potent islet mitogen, is capable of increasing islet mass, and is associated with hypoglycemia over the long term. It can be targeted to the beta cell using standard gene targeting techniques. Potential exists for beta cell engineering using this strategy.

BAC trimming: minimizing clone overlaps

Bacterial vectors containing large inserts of genomic DNA are now the standard substrates for large-scale genomic sequencing. Long overlaps between some clones lead to considerable redundant effort. A method for deleting defined regions from bacterial artificial chromosome (BAC) inserts, using homologous recombination, was applied to minimize the overlap between successive BAC clones. This procedure, called trimming, was carried out in the recA(-) BAC host. We have precisely deleted up to 70 kb of DNA from BACs that were to be sequenced. This method requires minimal prior characterization of the clones: collections of BAC end sequences or STS-based maps will accelerate the process. BAC trimming will be useful in both small and large genome sequencing projects and will be of particular utility for gap closure in finishing phases.

Hepatocyte growth factor overexpression in the islet of transgenic mice increases beta cell proliferation, enhances islet mass, and induces mild hypoglycemia

Hepatocyte growth factor (HGF) is produced in pancreatic mesenchyme-derived cells and in islet cells. In vitro, HGF increases the insulin content and proliferation of islets. To study the role of HGF in the islet in vivo, we have developed three lines of transgenic mice overexpressing mHGF using the rat insulin II promoter (RIP). Each RIP-HGF transgenic line displays clear expression of HGF mRNA and protein in the islet. RIP-mHGF mice are relatively hypoglycemic in post-prandial and fasting states compared with their normal littermates. They display inappropriate insulin production, striking overexpression of insulin mRNA in the islet, and a 2-fold increase in the insulin content in islet extracts. Importantly, beta cell replication rates in vivo are two to three times higher in RIP-HGF mice. This increase in proliferation results in a 2-3-fold increase in islet mass. Moreover, the islet number per pancreatic area was also increased by approximately 50%. Finally, RIP-mHGF mice show a dramatically attenuated response to the diabetogenic effects of streptozotocin. We conclude that the overexpression of HGF in the islet increases beta cell proliferation, islet number, beta cell mass, and total insulin production in vivo. These combined effects result in mild hypoglycemia and resistance to the diabetogenic effects of streptozotocin.

Breast cancer incidence highest in the range of one species of house mouse, Mus domesticus

Incidence of human breast cancer (HBC) varies geographically, but to date no environmental factor has explained this variation. Previously, we reported a 44% reduction in the incidence of breast cancer in women fully immunosuppressed following organ transplantation (Stewart et al (1995) Lancet 346: 796-798). In mice infected with the mouse mammary tumour virus (MMTV), immunosuppression also reduces the incidence of mammary tumours. DNA with 95% identity to MMTV is detected in 40% of human breast tumours (Wang et al (1995) Cancer Res 55: 5173-5179). These findings led us to ask whether the incidence of HBC could be correlated with the natural ranges of different species of wild mice. We found that the highest incidence of HBC worldwide occurs in lands where Mus domesticus is the resident native or introduced species of house mouse. Given the similar responses of humans and mice to immunosuppression, the near identity between human and mouse MTV DNA sequences, and the close association between HBC incidence and mouse ranges, we propose that humans acquire MMTV from mice. This zoonotic theory for a mouse-viral cause of HBC allows testable predictions and has potential importance in prevention.

Quantitative comparison of DNA looping in vitro and in vivo: chromatin increases effective DNA flexibility at short distances

The probability that two sites on a linear DNA molecule will contact each other by looping depends on DNA flexibility. Although the flexibility of naked DNA in vitro is well characterized, looping in chromatin is poorly understood. By extending existing theory, we present a single equation that describes DNA looping over all distances. We also show that DNA looping in vitro can be measured accurately by FLP recombination between sites from 74 bp to 15 kb apart. In agreement with previous work, a persistence length of 50 nm was determined. FLP recombination of the same substrates in mammalian cells showed that chromatin increases the flexibility of DNA at short distances, giving an apparent persistence length of 27 nm.

Papillary thyroid carcinoma metastatic to the pituitary gland

Many malignancies may present with metastases to the pituitary gland. The association of thyroid carcinoma with pituitary metastases is, however, very rare. This report describes two patients in whom metastases from a papillary thyroid carcinoma to the pituitary gland resulted in panhypopituitarism with blunted endogenous thyrotropin (TSH) production following withdrawal of levothyroxine. Both required the use of recombinant human TSH prior to radioiodine therapy. Symptoms of hypopituitarism may be difficult to distinguish clinically from those of hypothyroidism in the setting of levothyroxine withdrawal. Clinicians should be aware of the clinical and biochemical manifestations of this rare association.

Parathyroid hormone-related protein in rat penis: expression, localization, and effect on cavernosal pressure

Although PTH-related protein-(1-36) [PTHrP-(1-36)] is known to be expressed in smooth muscle and to exert potent myorelaxant effects, its tonic effects on cavernosal smooth muscle has not yet been explored. Using the RT-PCR technique, the present study establishes that PTHrP messenger RNA is present in microdissected corpus cavernosa in the rat. In immunohistochemical studies using affinity-purified antibodies to middle regions of PTHrP, immunostaining was localized throughout the penile structures, including vessels, cavernosal smooth muscle, and trabecular fibroblasts. Strong immunostaining for PTHrP was also detected in the dorsal nerve bundles. In anesthetized rats, intracavernosally injected boluses of increasing doses of PTHrP-(1-36) (0.3-30 pmol in 100 microl saline) had little effect on intracavernosal pressure. However, they markedly potentiated the dilatory response to papaverine (8-800 nmol), increasing the papaverine-induced intracavernous pressure by 2.5-fold, close to the mean arterial pressure. In conclusion, the cavernosal expression of PTHrP messenger RNA, the distribution of immunoreactive PTHrP throughout the structuro-functional components of the erectile apparatus and its strong potentiating action on papaverine-induced cavernosal relaxation, collectively suggest that PTHrP participates in the control of cavernosal tone.

Simplified generation of targeting constructs using ET recombination

ET recombination is a way to engineer DNA in Escherichia coli using homologous recombination. Here we develop the potential of ET recombination in two ways relevant to complex engineering exercises such as building gene targeting constructs. First, a targeting construct was made in a single step. Second, ET recombination was used to place two unique restriction sites at precise positions in a large genomic clone. Subsequently a complex targeting construct was created by ligation with a multifunctional cassette.

Therapeutic controversies in primary hyperparathyroidism

There is little debate about the primacy of surgery in the management of classical PHPT. Rather, the question has been what to do about the many patients with nonclassical disease. A 1990 NIH consensus conference (55) clearly recommended surgery for patients with significant adverse effects of PHPT, for patients with complicating coexistent illnesses, for younger patients, and for those in whom consistent long-term follow-up could not be assured. It allowed that conscientious surveillance may be justified in patients with minimal hypercalcemia and no adverse effects, but it recognized that for many patients, the time and expense involved in rigorous follow-up would outweigh the burden of surgery. Nine years later, the demonstrated prevalence of nonclassical symptoms and their reversibility, the evidence of "asymptomatic" but harmful effects reversible by surgery, and the accumulating evidence for surgical reduction of increased long-term mortality risk substantially strengthen the argument for surgery in such patients. For these reasons, parathyroidectomy should generally be recommended for patients with a secure diagnosis of PHPT, even in the absence of classical symptoms.