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Neurogenomic Profiling Reveals Distinct Gene Expression Profiles between Brain Parts that are Consistent in Ophthalmotilapia Cichlids

ABSTRACT: The detection of external and internal cues alters gene expression in the brain which in turn may affect neural networks that underly behavioral responses. Previous studies have shown that gene expression profiles differ between major brain regions within individuals and between species with different morphologies, cognitive abilities and/or behaviors. A detailed description of gene expression in all macroanatomical brain regions and in species with similar morphologies and behaviors is however lacking. Here, we dissected the brain of two cichlid species into six macroanatomical regions. Ophthalmotilapia nasuta and O. ventralis have similar morphology and behavior and occasionally hybridise in the wild. We use 3’ mRNA sequencing and a stage-wise statistical testing procedure to identify differential gene expression between females that were kept in a social setting with other females. Our results show that gene expression differs substantially between all six brain parts within species: out of 11 577 assessed genes, 8 748 are differentially expressed (DE) in at least one brain part compared to the average expression of the other brain parts. At most 16 % of these DE genes have |log2FC| significantly higher than two. Functional differences between brain parts were consistent between species. The majority (61 – 79 %) of genes that are DE in a particular brain part were shared between both species. Only 32 genes show significant differences in fold change across brain parts between species. These genes are mainly linked to transport, transmembrane transport, transcription (and its regulation) and signal transduction. Moreover, statistical equivalence testing reveals that within each comparison, on average 89 % of the genes show an equivalent fold change between both species. The pronounced differences in gene expression between brain parts and the conserved patterns between closely related species with similar morphologies and behavior suggest that unravelling the interactions between genes and behavior will benefit from neurogenomic profiling of distinct brain regions.

ORGANISM(S): Ophthalmotilapia ventralis Ophthalmotilapia nasuta

PROVIDER: GSE109106 | GEO | 2018/02/11

REPOSITORIES: GEO

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Project description:Fear conditioning (FC) is a behavioral paradigm that measures an animalâs ability to learn fear related information. FC is measured by pairing a mild foot-shock with the surroundings in which the shock was received. Upon being placed back in the context, mice exhibit freezing behavior, which is a species-specific response to fear. We have used selective breeding to produce lines of mice with high or low levels of freezing behavior. We are able to identify alleles that govern the genetic variability for FC by using chromosomal markers in these lines. Using microarrays, we will identify differences in gene expression in two key brain regions: amygdala and hippocampus. Gene expression differences and data regarding chromosomal regions involved in the behavior will be compared to identify particular genes that are both differentially expressed and whose expression is governed by alleles that fall into critical chromosomal regions.,We will compare gene expression in the amygdala and hippocampus (brain regions known to be relevant to fear behavior) from the two lines of mice and use Bayesian statistics in an effort to identify gene expression that affects fear behavior.,We hypothesize that selection has acted in part by changing the frequency of alleles that cause differential expression of key genes in the amygdala and hippocampus of our selected lines. Selective breeding changes the frequency of trait relevant (FC) alleles. A relevant allele is expected to increase in one selected line and decrease in the oppositely selected line. Some trait relevant alleles are expected cause changes in the level of expression at particular genes.,Amygdala and hippocampus will be rapidly dissected out of experimentally naÃ¯ve mice from each line. NaÃ¯ve mice will be used for expression studies since the behavior of the mice in the FC test can be reliably anticipated due to their lineage. We have practiced these procedures, and can accurately and reproducibly remove these regions in less than 5 minutes. Different mice will be used to collect each brain region, since the dissection of hippocampus disrupts the removal of amygdala. We will collect enough samples from each region to accommodate a total of 6 microarrays per brain region, per line, thus we will use a total of 24 microarrays. We anticipate that a single brain region will be sufficient to for a microarray. However, we propose to utilize three samples per microarray, because this will reduce variability due to environmental factors and due to slight variability in our dissection procedures. Once this tissue is removed, we will isolate RNA for shipment to the Microarray consortium. We will also collect spleens from each subject as a source of genomic DNA, in order to permit direct comparison of genotype and expression phenotypes. Once we have the results of the microarray analysis, we use WebQTL.org to identify the chromosomal locations of alleles that are know to influence the expression of genes for which we have found differential expression. We will then superimpose this information on trait relevant chromosomal regions identified from our selected lines. This will allow us to rapidly identify genes which may account for genetic variability in FC due to differential expression. Such genes will then be subjected to further study.

Project description:Fear conditioning (FC) is a behavioral paradigm that measures an animal's ability to learn fear related information. FC is measured by pairing a mild foot-shock with the surroundings in which the shock was recieved. Upon being placed back in the context, mice exhibit freezing behavior, which is a species-specific response to fear. We have previously used selective breeding to produce lines of mice with high or low levels of freezing behavior. This experiment is a replication of a previous experiment that produced lines of mice with high or low levels of freezing behavior. These lines derive from different progenitor mouse strains. We are able to identify alleles that govern the genetic variability for FC by using chromosomal markers in these selected lines. Using microarrays, we will identify differences in gene expression in two key brain regions: amygdala and hippocampus. Gene expression differences and data regarding chromosomal regions involved in the behavior will be compared to identify particular genes that are both differentially expressed and whose expression is governed by alleles that fall into critical chromosomal regions.,We will compare gene expresion in the amygdala and hippocampus (brain regions known to be relevant to fear behavior) from the these two lines of mice and to the those in the previous experiment. Bayesian statistics will be used in an effort to identify gene expression that affects fear behavior.,We hypothesize that selection has acted in part by changing the frequency of alleles that cause differential expression of key genes in the amygdala and hippocampus of our selected lines. Slective breeding changes the frequency of trait relevand (FC) alleles. A relevant allele is expected to increas in one selected line and decrease in the oppositely selected line. Some trait relevant alleles are expected to cause changes in the level of expression at particular genes.,Amygdala and hippocampus will be rapidly dissected out of experimentally naÃ¯ve mice from each line. NaÃ¯ve mice will be used for expression studies since the behavior of the mice in the FC test can be reliably anticipated due to their lineage. We have practiced these procedures, and can accurately and reproducibly remove these regions in less than 5 minutes. Different mice will be used to collect each brain region, since the dissection of hippocampus disrupts the removal of amygdala. We will collect enough samples from each region to accommodate a total of 6 microarrays per brain region, per line, thus we will use a total of 24 microarrays. We anticipate that a single brain region will be sufficient to for a microarray. However, we propose to utilize three samples per microarray, because this will reduce variability due to environmental factors and due to slight variability in our dissection procedures. Once this tissue is removed, we will isolate RNA for shipment to the Microarray consortium. We will also collect spleens from each subject as a source of genomic DNA, in order to permit direct comparison of genotype and expression phenotypes. Once we have the results of the microarray analysis, we use WebQTL.org to identify the chromosomal locations of alleles that are know to influence the expression of genes for which we have found differential expression. We will then superimpose this information on trait relevant chromosomal regions identified from our selected lines. This will allow us to rapidly identify genes which may account for genetic variability in FC due to differential expression. Such genes will then be subjected to further study.

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Neurogenomic Profiling Reveals Distinct Gene Expression Profiles between Brain Parts that are Consistent in Ophthalmotilapia Cichlids

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