Enhancement of pentobarbital effect by continuous administration of morphine in the mouse

These studies demonstrated that continuous morphine treatment from implantation of a 75 mg morphine pellet for 3 days potentiated pentobarbital narcosis and enhanced pentobarbital hypothermia. In the morphine implant mice, sleeping time after two different doses of pentobarbital was greater than 2.5 × the sleeping time in placebo pellet implant animals and also greater than sleeping time in animals treated acutely with morphine prior to pentobarbital. Moreover, in the morphine implant mice both the degree and duration of pentobarbital induced hypothermia were enhanced. The above findings were due to slower rate of metabolism of pentobarbital as evidenced by inhibition of hepatic N-demethylation, and higher levels of brain and serum pentobarbital in the morphine implant mice compared to both placebo and acute morphine mice.     

Marker assisted breeding for transformability in maize

Corn lines with improved culturability and transformability were produced using Marker Assisted Breeding (MAB) to introgress specific regions from the highly transformable hybrid, Hi-II, into the elite line, FBLL that responds very poorly in culture. FBLL is a female inbred parental stiff-stalk line that has been used to produce a series of some of DEKALB’s historically best selling hybrids. Five unlinked regions important for culturability and transformability were identified by segregation distortion analysis and introgressed into FBLL to produce the highly transformable FBLL-MAB lines. Agrobacterium mediated transformation was used to screen the FBLL-MAB lines and select the most efficient lines for transformation using immature embryo explants. Two highly efficient transformation systems were developed using kanamycin and glyphosate as selective agents. To evaluate agronomics, two testcross hybrids were produced for each of the three lead FBLL-MAB lines. A 25-location, 3-replication yield trial was used to evaluate grain yield, yield stability, and agronomic characteristics of the hybrids. Yields were found to be 2–5% lower and more stable (across a diverse set of environments) among hybrids produced with the FBLL-MAB lines as compared to the same hybrids produced with FBLL.     

Intra-Genomic Variation in the Ribosomal Repeats of Nematodes

Ribosomal loci represent a major tool for investigating environmental diversity and community structure via high-throughput marker gene studies of eukaryotes (e.g. 18S rRNA). Since the estimation of species’ abundance is a major goal of environmental studies (by counting numbers of sequences), understanding the patterns of rRNA copy number across species will be critical for informing such high-throughput approaches. Such knowledge is critical, given that ribosomal RNA genes exist within multi-copy repeated arrays in a genome. Here we measured the repeat copy number for six nematode species by mapping the sequences from whole genome shotgun libraries against reference sequences for their rRNA repeat. This revealed a 6-fold variation in repeat copy number amongst taxa investigated, with levels of intragenomic variation ranging from 56 to 323 copies of the rRNA array. By applying the same approach to four C. elegans mutation accumulation lines propagated by repeated bottlenecking for an average of ~400 generations, we find on average a 2-fold increase in repeat copy number (rate of increase in rRNA estimated at 0.0285-0.3414 copies per generation), suggesting that rRNA repeat copy number is subject to selection. Within each Caenorhabditis species, the majority of intragenomic variation found across the rRNA repeat was observed within gene regions (18S, 28S, 5.8S), suggesting that such intragenomic variation is not a product of selection for rRNA coding function. We find that the dramatic variation in repeat copy number among these six nematode genomes would limit the use of rRNA in estimates of organismal abundance. In addition, the unique pattern of variation within a single genome was uncorrelated with patterns of divergence between species, reflecting a strong signature of natural selection for rRNA function. A better understanding of the factors that control or affect copy number in these arrays, as well as their rates and patterns of evolution, will be critical for informing estimates of global biodiversity.