Lamin B1 is essential for neuronal migration and progenitor proliferation during the development of the cerebral cortex. The observation of distinct phenotypes of Lmnb1- and Lmnb2-knockout mice and the differences in the nuclear morphology of cortical neurons in vivo suggest that lamin B1 and lamin B2 play distinct functions in the developing brain.

Nuclear lamins are components of the nuclear lamina, a structural scaffolding for the cell nucleus. Defects in lamins A and C cause an array of human diseases, including muscular dystrophy, lipodystrophy, and progeria, but no diseases have been linked to the loss of lamins B1 or B2. To explore the functional relevance of lamin B2, we generated lamin B2-deficient mice and found that they have severe brain abnormalities resembling lissencephaly, with abnormal layering of neurons in the cerebral cortex and cerebellum. This neuronal layering abnormality is due to defective neuronal migration, a process that is dependent on the organized movement of the nucleus within the cell. These studies establish an essential function for lamin B2 in neuronal migration and brain development.brain | lissencephaly | neuronal migration | nuclear envelope | nuclear lamina T he nuclear lamina is an intermediate filament meshwork lying beneath the inner nuclear membrane that provides a structural scaffolding for the nucleus (1). The lamina is also important for other processes, including gene transcription, chromatin organization, nuclear pore distribution, nuclear envelope assembly, and tethering of the nucleus to the cytoskeleton (1, 2). The main components of the nuclear lamina are nuclear lamins, a class of intermediate filament proteins that is generally divided into two groups, A-type (lamins A and C) and B-type (lamins B1 and B2) (3, 4). Lamins A and C are produced from LMNA by alternative splicing, whereas lamins B1 and B2 are encoded by distinct genes, LMNB1 and LMNB2, respectively. Lamins B1 and B2 are expressed in all cells and throughout development, whereas lamins A and C are expressed in differentiated cells, beginning at midgestation (3).Interest in the nuclear lamins has intensified with the discovery that over a dozen human diseases, including muscular dystrophy, cardiomyopathy, lipodystrophy, and progeria, are caused by mutations in LMNA (5-7). To date, more than 340 missense, nonsense, frameshift, and splicing mutations have been identified (5). In contrast, no human diseases have been linked to these types of mutations in LMNB1 and LMNB2, and, so far, the only clear-cut association between B-type lamins and disease has been the finding of LMNB1 gene duplications in autosomal-dominant leukodystrophy (8).The paucity of "lamin B diseases" is probably not due to complete redundancy of lamins B1 and B2, as Lmnb1-deficient mice are small during embryonic development and die soon after birth with defects in lungs and bones (9). Also, Lmnb1-deficient fibroblasts display misshapen cell nuclei, aneuploidy, and early senescence (9). To further examine the functional importance of the B-type lamins, we generated Lmnb2-deficient mice.

Lamin A and lamin C, both products of Lmna, are key components of the nuclear lamina. In the mouse, a deficiency in both lamin A and lamin C leads to slow growth, muscle weakness, and death by 6 weeks of age. Fibroblasts deficient in lamins A and C contain misshapen and structurally weakened nuclei, and emerin is mislocalized away from the nuclear envelope. The physiologic rationale for the existence of the 2 different Lmna products lamin A and lamin C is unclear, although several reports have suggested that lamin A may have particularly important functions, for example in the targeting of emerin and lamin C to the nuclear envelope. Here we report the development of lamin C-only mice (Lmna LCO/LCO ), which produce lamin C but no lamin A or prelamin A (the precursor to lamin A). Lmna LCO/LCO mice were entirely healthy, and Lmna LCO/LCO cells displayed normal emerin targeting and exhibited only very minimal alterations in nuclear shape and nuclear deformability. Thus, at least in the mouse, prelamin A and lamin A appear to be dispensable. Nevertheless, an accumulation of farnesyl-prelamin A (as occurs with a deficiency in the prelamin A processing enzyme Zmpste24) caused dramatically misshapen nuclei and progeria-like disease phenotypes. The apparent dispensability of prelamin A suggested that lamin A-related progeroid syndromes might be treated with impunity by reducing prelamin A synthesis. Remarkably, the presence of a single Lmna LCO allele eliminated the nuclear shape abnormalities and progeria-like disease phenotypes in Zmpste24 -/-mice. Moreover, treating Zmpste24 -/-cells with a prelamin A-specific antisense oligonucleotide reduced prelamin A levels and significantly reduced the frequency of misshapen nuclei. These studies suggest a new therapeutic strategy for treating progeria and other lamin A diseases.

HIV protease inhibitors (HIV-PIs

Nuclear lamins are usually classified as A-type (lamins A and C) or B-type (lamins B1 and B2). A-type lamins have been implicated in multiple genetic diseases but are not required for cell growth or development. In contrast, B-type lamins have been considered essential in eukaryotic cells, with crucial roles in DNA replication and in the formation of the mitotic spindle. Knocking down the genes for B-type lamins (LMNB1, LMNB2) in HeLa cells has been reported to cause apoptosis. In the current study, we created conditional knockout alleles for mouse Lmnb1 and Lmnb2, with the goal of testing the hypothesis that B-type lamins are crucial for the growth and viability of mammalian cells in vivo. Using the keratin 14-Cre transgene, we bred mice lacking the expression of both Lmnb1 and Lmnb2 in skin keratinocytes (Lmnb1(Δ/Δ)Lmnb2(Δ/Δ)). Lmnb1 and Lmnb2 transcripts were absent in keratinocytes of Lmnb1(Δ/Δ)Lmnb2(Δ/Δ) mice, and lamin B1 and lamin B2 proteins were undetectable. But despite an absence of B-type lamins in keratinocytes, the skin and hair of Lmnb1(Δ/Δ)Lmnb2(Δ/Δ) mice developed normally and were free of histological abnormalities, even in 2-year-old mice. After an intraperitoneal injection of bromodeoxyuridine (BrdU), similar numbers of BrdU-positive keratinocytes were observed in the skin of wild-type and Lmnb1(Δ/Δ)Lmnb2(Δ/Δ) mice. Lmnb1(Δ/Δ)Lmnb2(Δ/Δ) keratinocytes did not exhibit aneuploidy, and their growth rate was normal in culture. These studies challenge the concept that B-type lamins are essential for proliferation and vitality of eukaryotic cells.

Public-sector planning problems are typically complex, and some important planning issues cannot be captured within a mathematical programming model of a problem; such issues may be qualitative in nature, unknown, or unrevealed by decisionmakers. Furthermore, there are often numerous solutions to a mathematical formulation that are nearly the same with respect to modeled issues but that are drastically different from each other in decision space. In such cases, some of these solutions may be significantly better than others with respect to unmodeled issues. Thus, a potentially important role of programming models is to generate a small number of alternative solutions that are feasible, perform well with respect to modeled issues, and are significantly different with respect to the decisions they specify. Such a set of alternatives may aid analysts and decision makers in understanding the problem and may serve as a catalyst for human creativity and invention. The Hop, Skip, and Jump (HSJ) method has been developed for this purpose. It is designed to produce alternative solutions that are very different from previously generated solutions. Each solution generated is good in the sense that it meets targets specified for modeled objectives. The technique is described in this paper, and is illustrated using a multiobjective linear programming model of a land use planning problem provided by a regional planning commission. In this case, the method is shown to be capable of generating alternative solutions that perform well with respect to the modeled objectives and that are drastically different with respect to the land use pattern specified. Differences among solutions are discussed using visual inspection as well as simple quantitative measures. The technique can be used to extend the capabilities of existing mathematical programming packages.mathematical programming, policy analysis, planning

Change in carotid corrected flow time can predict fluid responsiveness status after a passive leg raise maneuver. Using point-of-care ultrasound to assess change in carotid corrected flow time is an acceptable and reproducible method for noninvasive identification of fluid responsiveness in critically ill patients with undifferentiated shock.

Hutchinson-Gilford progeria syndrome (HGPS) is caused by a mutant prelamin A, progerin, that terminates with a farnesylcysteine. HGPS knock-in mice (Lmna(HG/+)) develop severe progeria-like disease phenotypes. These phenotypes can be ameliorated with a protein farnesyltransferase inhibitor (FTI), suggesting that progerin's farnesyl lipid is important for disease pathogenesis and raising the possibility that FTIs could be useful for treating humans with HGPS. Subsequent studies showed that mice expressing non-farnesylated progerin (Lmna(nHG/+) mice, in which progerin's carboxyl-terminal -CSIM motif was changed to -SSIM) also develop severe progeria, raising doubts about whether any treatment targeting protein prenylation would be particularly effective. We suspected that those doubts might be premature and hypothesized that the persistent disease in Lmna(nHG/+) mice could be an unanticipated consequence of the cysteine-to-serine substitution that was used to eliminate farnesylation. To test this hypothesis, we generated a second knock-in allele yielding non-farnesylated progerin (Lmna(csmHG)) in which the carboxyl-terminal -CSIM motif was changed to -CSM. We then compared disease phenotypes in mice harboring the Lmna(nHG) or Lmna(csmHG) allele. As expected, Lmna(nHG/+) and Lmna(nHG/nHG) mice developed severe progeria-like disease phenotypes, including osteolytic lesions and rib fractures, osteoporosis, slow growth and reduced survival. In contrast, Lmna(csmHG/+) and Lmna(csmHG/csmHG) mice exhibited no bone disease and displayed entirely normal body weights and survival. The frequencies of misshapen cell nuclei were lower in Lmna(csmHG/+) and Lmna(csmHG/csmHG) fibroblasts. These studies show that the ability of non-farnesylated progerin to elicit disease depends on the carboxyl-terminal mutation used to eliminate protein prenylation.