ABSTRACT The pulmonate freshwater snail Promenetus exacuous (Planorbidae) has a widespread patchy distribution throughout much of North America, including New York State and the surrounding areas. Minimal life history information exists for the species in this region and information on its genetic diversity and structure is currently lacking for any portion of its range. We examined the species’ reproductive behaviour, genetic diversity and population structure throughout New York and western Connecticut using cytochrome c oxidase subunit I (COI) haplotypes (241 snails) and 10 microsatellite loci (312 snails). Throughout the region, P. exacuous is a single, primarily outcrossing species with relatively high within-population genetic diversity. Populations are genetically differentiated and composed of divergent COI lineages. The region was colonized after the Wisconsin glacial retreat by snails from multiple, historically isolated populations and Pleistocene events played a major role in the historical diversification of lineages. Subsequent dispersal has likely been facilitated by birds and humans, but contemporary gene flow is low, resulting in genetic differentiation even among geographically proximate sites. Our data reveal that complex interactions between historical and contemporary processes contribute to the overall patterns of genetic diversity in freshwater snails.
Promenetus exacuous and Valvata tricarinata are freshwater snail species with widespread distributions throughout North America. Information regarding their genetic diversity and population connectivity are currently lacking. We utilized next generation sequencing to develop the first microsatellites for each species to investigate genetic diversity within and differentiation among populations.Sixteen and seventeen microsatellite loci were developed for P. exacuous and V. tricarinata, respectively, and tested in a total of 43 P. exacuous and 48 V. tricarinata from two lakes approximately 183 km apart in New York State, USA. Fifteen P. exacuous loci were polymorphic in at least one lake and possessed 1-23 alleles and observed heterozygosities of 0.00-0.96 within individual lakes. Seventeen polymorphic V. tricarinata loci possessed 2-19 alleles and observed heterozygosities of 0.04-0.96 within lakes. Bayesian clustering using 12 loci for each species identified two distinct genetic populations, reflecting the two lakes. High assignment scores for individual snails to the lakes they were collected from supported strong population structure with minimal admixture at the scale of this study. These loci will be useful for investigating the genetic diversity and population structure of these species and indicate genetic differentiation may be common among their populations.
Investigate the molecular determinants of retinal regeneration in adult vertebrates by analyzing the gene expression of control and post-lesion retina of adult zebrafish, a system that regenerates following injury.Gene expression of zebrafish retina and brain were determined with DNA microarray, RT-PCR, and real-time quantitative PCR analyses. Damaged retinas and their corresponding controls were analyzed 2-5 days post-lesion (acute injury condition) or 14 d post-lesion (cell regeneration condition).Expected similarities and differences in the gene expression profile of zebrafish retina and brain were observed, confirming the applicability of the gene expression techniques. Mechanical lesion of retina triggered significant, time-dependent changes in retinal gene expression. The induced transcriptional changes were consistent with cellular phenomena known to occur, in a time-dependent manner, subsequent to retinal lesion, including cell cycle progression, axonal regeneration, and regenerative cytogenesis.The results indicate that retinal regeneration in adult zebrafish involves a complex set of induced, targeted changes in gene transcription, and suggest that these molecular changes underlie the ability of the adult vertebrate retina to regenerate.
Fish can regenerate retinal neurons following ocular injury. Evidence is mounting that astrocytic glia function as inducible, regenerative stem cells in this process, but the underlying molecular events that enable neuronal regeneration are comparatively unclear. In the current study gene array, quantitative real-time PCR, in situ hybridization, and immunohistochemical approaches were used to identify, in the damaged retina of adult zebrafish, correlations between transcriptional events and entry into the cell cycle by Müller cells, a type of astrocytic cell present in all vertebrate retinas that is a candidate 'stem cell' of regenerated neurons. A proneural gene (achaete-scute homolog 1a, ash1a) and neurogenic components of the Notch signaling pathway, including notch3 and deltaA, were implicated. An injury-induced, enhanced expression of ash1a was observed in Müller cells, which is hypothesized to contribute to the transition of these cells, or their cellular progeny, into a notch3-expressing, regenerative progenitor. A model of vertebrate retinal repair is suggested in which damage-induced expression of proneural genes, plus canonical Notch-Delta signaling, could contribute to retinal stem cell promotion and subsequent regenerative neurogenesis.
