The detection and estimation of linkage in polyploids using single-dose restriction fragments

Summary Restriction fragment length polymorphism (RFLP) linkage maps have been constructed in several major diploid crops. However, construction of RFLP maps directly in polyploids has lagged behind for several reasons: (1) there are a large number of possible genotypes for each DNA probe expected in a segregating population, and these genotypes cannot always be identified readily by their banding phenotypes; and (2) the genome constitutions (allopolyploidy versus autopolyploidy) in many high polyploids are not clearly understood. We present here an analysis of these problems and propose a general method for mapping polyploids based on segregation of single-dose restriction fragments (SDRFS). SDRFs segregate 1:1 (presence: absence) in gametes of heterozygous plants. Hypothetical allopolyploid and autopolyploid species with four ploidy levels of 2n = 4x, 6x, 8x, and 10x, are used to illustrate the procedures for identifying SDRFs, detecting linkages among SDRFs, and distinguishing allopolyploid versus autopolyploids from polyploids of unknown genome constitution. Family size required, probability of linkage, and attributes of different mapping populations are discussed. We estimate that a population size of 75 is required to identify SDRFs with 98% level of confidence for the four ploidy levels. This population size is also adequate for detecting and estimating linkages in the coupling phase for both allopolyploids and autopolyploids, but linkages in the repulsion phase can be estimated only in allopolyploids. For autopolyploids, it is impractical to estimate meaningful linkages in repulsion because very large family sizes (>750) are required. For high-level polyploids of unknown genome constitution, the ratio between the number of detected repulsion versus coupling linkages may provide a crude measurement of preferential chromosome pairing, which can be used to distinguish allopolyploidy from autopolyploidy. To create a mapping population, one parent (P₁) should have high heterozygosity to ensure a high frequency of SDRFs, and the second parent (P₂) should have a low level of heterozygosity to increase the probability of detecting polymorphic fragments. This condition could be satisfied by choosing outcrossed hybrids as one parental type and inbreds, haploids, or doubled haploids as the other parental type.Published as Paper No. 730 in the Journal Series of the Experiment Station, Hawaiian Sugar Planters' Association, and as Paper No. 792 in the Plant Breeding Series of Cornell University, Ithaca, NY 14853, USA     

Effect of Age-Stiffening Tissues and Intraocular Pressure on Optic Nerve Damages

Age-stiffening of ocular tissues is statistically linked to glaucoma in the elderly. In this study, the effects of age-stiffening on the lamina cribrosa, the primary site of glaucomatous nerve damages, were modeled using computational finite element analysis. We showed that glaucomatous nerve damages and peripheral vision loss behavior can be phenomenologically modeled by shear-based damage criterion. Using this damage criterion, the potential vision loss for 30 years old with mild hypertension of 25mmHg intraocular pressure (IOP) was estimated to be 4%. When the IOP was elevated to 35mmHg, the potential vision loss rose to 45%; and age-stiffening from 35 to 60 years old increased the potential vision loss to 52%. These results showed that while IOP plays a central role in glaucomatous damages, age-stiffening facilitates glaucomatous damages and may be the principal factor that resulted in a higher rate of glaucoma in the elderly than the general population.     

Genbank accession #: AJ133707

Plant Molecular Biology -     

Genbank accession #: AJ237597

Plant Molecular Biology -     

Genbank accession #: 133708

Plant Molecular Biology -     

Improvement in in?vitro fertilization outcome following in?vivo synchronization of oocyte maturation in mice

Synchronization of oocyte maturation in vitro has been shown to produce higher in vitro fertilization (IVF) rates than those observed in oocytes matured in vitro without synchronization. However, the increased IVF rates never exceeded those observed in oocytes matured in vivo without synchronization. This study was therefore designed to define the effect of in vivo synchronization of oocyte maturation on IVF rates. Mice were superovulated and orally treated with 7.5 mg cilostazol (CLZ), a phosphodiesterase 3A (PDE3A) inhibitor, to induce ovulation of immature oocytes at different stages depending on frequency and time of administration of CLZ. Mice treated with CLZ ovulated germinal vesicle (GV) or metaphase I (MI) oocytes that underwent maturation in vitro or in vivo (i.e. in the oviduct) followed by IVF. Superovulated control mice ovulated mature oocytes that underwent IVF directly upon collection. Ovulated MI oocytes matured in vitro or in vivo had similar maturation rates but significantly higher IVF rates, 2–4 cell embryos, than those observed in control oocytes. Ovulated GV oocytes matured in vitro showed similar maturation rates but significantly higher IVF rates than those observed in control oocytes. However, ovulated GV oocytes matured in vivo had significantly lower IVF rates than those noted in control oocytes. It is concluded that CLZ is able to synchronize oocyte maturation and improve IVF rates in superovulated mice. CLZ may be capable of showing similar effects in humans, especially since temporal arrest of human oocyte maturation with other PDE3A inhibitors in vitro was found to improve oocyte competence level. The capability of a clinically approved PDE3A inhibitor to improve oocyte fertilization rates in mice at doses extrapolated from human therapeutic doses suggests the potential scenario of the inclusion of CLZ in superovulation programs. This may improve IVF outcomes in infertile patients.