Expression of the eight GABAA receptor α subunits in the developing zebrafish central nervous system.

GABA is a robust regulator of both developing and mature neural networks. It exerts many of its effects through GABAA receptors, which are heteropentamers assembled from a large array of subunits encoded by distinct genes. In mammals, there are 19 different GABAA subunit types, which are divided into the α, ß, γ, δ, ε, π, θ and ρ subfamilies. The immense diversity of GABAA receptors is not fully understood. However, it is known that specific isoforms, with their distinct biophysical properties and expression profiles, tune responses to GABA. Although larval zebrafish are well-established as a model system for neural circuit analysis, little is known about GABAA receptors diversity and expression in this system. Here, using database analysis, we show that the zebrafish genome contains at least 23 subunits. All but the mammalian θ and ε subunits have at least one zebrafish ortholog, while five mammalian GABAA receptor subunits have two zebrafish orthologs. Zebrafish contain one subunit, ß4, which does not have a clear mammalian ortholog. Similar to mammalian GABAA receptors, the zebrafish α subfamily is the largest and most diverse of the subfamilies. In zebrafish there are eight α subunits, and RNA in situ hybridization across early zebrafish development revealed that they demonstrate distinct patterns of expression in the brain, spinal cord, and retina. Some subunits were very broadly distributed, whereas others were restricted to small populations of cells. Subunit-specific expression patterns in zebrafish resembled were those found in frogs and rodents, which suggests that the roles of different GABAA receptor isoforms are largely conserved among vertebrates. This study provides a platform to examine isoform specific roles of GABAA receptors within zebrafish neural circuits and it highlights the potential of this system to better understand the remarkable heterogeneity of GABAA receptors.

A review of the prevalence, utility, and caveats of using chloroplast simple sequence repeats for studies of plant biology.

Microsatellites occur in all plant genomes and provide useful markers for studies of genetic diversity and structure. Chloroplast microsatellites (cpSSRs) are frequently targeted because they are more easily isolated than nuclear microsatellites. Here, we quantified the frequency and uses of cpSSRs based on a literature review of over 400 studies published 1995-2013. These markers are an important and economical tool for plant biologists and continue to be used alongside modern genomics approaches to study genetic diversity and structure, evolutionary history, and hybridization in native and agricultural species. Studies using species-specific primers reported a greater number of polymorphic loci than those employing universal primers. A major disadvantage to cpSSRs is fragment size homoplasy; therefore, we documented its occurrence at several cpSSR loci within and between species of Acmispon (Fabaceae). Based on our empirical data set, we recommend targeted sequencing of a subset of samples combined with fragment genotyping as a cost-efficient, data-rich approach to the use of cpSSRs and as a test of homoplasy. The availability of genomic resources for plants aids in the development of primers for new study systems, thereby enhancing the utility of cpSSRs across plant biology.