Emerging mechanisms and roles of meiotic crossover repression at centromeres.

Crossover events during recombination in meiosis are essential for generating genetic diversity as well as crucial to allow accurate chromosomal segregation between homologous chromosomes. Spatial control for the distribution of crossover events along the chromosomes is largely a tightly regulated process and involves many facets such as interference, repression as well as assurance, to make sure that not too many or too few crossovers are generated. Repression of crossover events at the centromeres is a highly conserved process across all species tested. Failure to inhibit such recombination events can result in chromosomal mis-segregation during meiosis resulting in aneuploid gametes that are responsible for infertility or developmental disorders such as Down's syndrome and other trisomies in humans. In the past few decades, studies to understand the molecular mechanisms behind this repression have shown the involvement of a multitude of factors ranging from the centromere-specific proteins such as the kinetochore to the flanking pericentric heterochromatin as well as DNA double-strand break repair pathways. In this chapter, we review the different mechanisms of pericentric repression mechanisms known till date as well as highlight the importance of understanding this regulation in the context of chromosomal segregation defects. We also discuss the clinical implications of dysregulation of this process, especially in human reproductive health and genetic diseases.

Community responses to government defunding of watershed projects: a comparative study in India and the USA.

When central governments decentralize natural resource management (NRM), they often retain an interest in the local efforts and provide funding for them. Such outside investments can serve an important role in moving community-based efforts forward. At the same time, they can represent risks to the community if government resources are not stable over time. Our focus in this article is on the effects of withdrawal of government resources from community-based NRM. A critical question is how to build institutional capacity to carry on when the government funding runs out. This study compares institutional survival and coping strategies used by community-based project organizations in two different contexts, India and the United States. Despite higher links to livelihoods, community participation, and private benefits, efforts in the Indian cases exhibited lower survival rates than did those in the U.S. cases. Successful coping strategies in the U.S. context often involved tapping into existing institutions and resources. In the Indian context, successful coping strategies often involved building broad community support for the projects and creatively finding additional funding sources. On the other hand, the lack of local community interest, due to the top-down development approach and sometimes narrow benefit distribution, often challenged organizational survival and project maintenance.

Development of optimal medium for production of commercially important monoclonal antibody 520C9 by hybridoma cell.

Hybridoma HB-8696 produces monoclonal antibody (mAb) 520C9 (mouse IgG(1)), which recognizes breast cancer oncoprotein c-erbB2. The objective of this study was to optimize the medium recipe of HB 8696 cell for production of mAb 520C9. The optimization consisted of two steps: (1) screening of significant nutrients to make subsequent experiments more efficient with less runs and (2) locating their optimal concentrations. 29 variables including essential and non-essential amino acids, glucose, serum and 6 salts, namely NaCl, KCl, CaCl(2), NaH(2)PO(4), MgSO(4) and Na-pyruvate were chosen in screening phase. The Plackett-Burman method was used to screen the variables influencing mAb production. Seven factors namely glucose, serum, asparagine, threonine, serine, NaCl and NaH(2)PO(4) were identified to have a positive influencing role on mAb production with a confidence level >90 % (p < 0.1). Finally, Response surface methodology revealed the optimal level of the variables. The mAb production and average specific mAb production rate were enhanced by 111.05 and 105 %, respectively, compared to control medium.

Step-up/step-down perfusion approach for increased mAb 520C9 production by a hybridoma cell line.

The hybridoma cell line, HB-8696, produces a monoclonal antibody, 520C9 (mouse IgG(1)) that recognizes the breast cancer oncoprotein, c-erbB2. The effect of perfusion rate (volume of fresh feed/working volume of reactor/day) on cell growth and mAb production was investigated but perfusion at a constant rate and at an arbitrarily increased rate could not maintain exponential cell growth or a higher specific mAb production rate. An optimum step-up/step-down perfusion strategy is therefore proposed for maintaining a steady state production phase at high cell density for ten days. The optimum step-up perfusion could achieve fast cell growth by avoiding any nutrient limited condition and the following optimum step-down perfusion could potentially maintain high live cell density and reduced product dilution as well. The maximum viable cell achieved under optimum perfusion strategy was 2.3 × 10(7) cells/ml which was 19-fold higher than in optimum batch culture. The mAb yield and volumetric productivity were significantly improved to 52 and 50 mg/l day compared to 25 and 3.8 mg/l day in optimum batch, respectively, and could be maintained for up to ten days.

Production, purification, immobilization, and characterization of a thermostable ß-galactosidase from Aspergillus alliaceus.

A fungal strain isolated from rotten banana and identified as Aspergillus alliaceus was found capable of producing thermostable extracellular ß-galactosidase enzyme. Optimum cultural conditions for ß-galactosidase production by A. alliaceus were as follows: pH 4.5; temperature, 30 °C; inoculum age, 25 h; and fermentation time, 144 h. Optimum temperature, time, and pH for enzyme substrate reaction were found to be 45 °C, 20 min, and 7.2, respectively, for crude and partially purified enzyme. For immobilized enzyme-substrate reaction, these three variable, temperature, time, and pH were optimized at 50 °C, 40 min, and 7.2, respectively. Glucose was found to inhibit the enzyme activity. The K(m) values of partially purified and immobilized enzymes were 170 and 210 mM, respectively. Immobilized enzyme retained 43 % of the ß-galactosidase activity of partially purified enzyme. There was no significant loss of activity on storage of immobilized beads at 4 °C for 28 days. Immobilized enzyme retained 90 % of the initial activity after being used four times.

Methylphenidate treatment in adolescent rats with an attention deficit/hyperactivity disorder phenotype: cocaine addiction vulnerability and dopamine transporter function.

Appropriate animal models of attention deficit/hyperactivity disorder (ADHD) and drug reinforcement allow investigation of possible underlying biological bases of ADHD and its comorbidity with cocaine addiction. Toward this end, spontaneously hypertensive rats (SHRs) exhibiting an ADHD phenotype were compared with Wistar-Kyoto (WKY) and Wistar (WIS) rats. Initially, 1.5 mg/kg oral methylphenidate or vehicle was administered between postnatal days 28 and 55, and acquisition of visual discrimination learning was examined. After discontinuing adolescent treatments, adult rats were evaluated for cocaine self-administration and dopamine transporter (DAT) function in the prefrontal cortex (PFC) and striatum. During adolescence, SHRs showed deficits in visual discrimination relative to WKY and WIS rats when non-medicated. Methylphenidate improved visual discrimination only in SHRs. Compared with WKY and WIS rats, SHRs with previous methylphenidate treatment acquired cocaine self-administration faster, identified cocaine as a highly efficacious reinforcer by displaying an upward shift in the cocaine dose-response function, and showed the greatest motivation to self-administer cocaine by exhibiting the highest progressive ratio breakpoints. In the PFC, the maximal dopamine uptake (V(max)) at DAT was decreased in SHRs and increased in WKY and WIS rats by previous methylphenidate treatment. The affinity (K(m)) for dopamine at DAT in the PFC was not different between strains, nor was V(max) or K(m) altered in the striatum by previous methylphenidate treatment in any strain. Methylphenidate-induced decreases in dopamine clearance by DAT in the PFC may underlie increased cocaine self-administration in SHRs. These preclinical findings suggest that caution should be exercised when methylphenidate is prescribed for first-time treatment of ADHD in adolescent patients, as cocaine addiction vulnerability may be augmented.