Truncated dopamine transporter's epigenetics: Heterozigosity of the grandmother rat temperates the vulnerable phenotype in second-generation offspring.

Behavioral phenotype differs among epigenotypes of dopamine-transporter heterozygous (DAT-HET) rats. Epigenetic regulations act through transgenerational effects, referring to phenotypic variations emerging at second or third generation. To investigate transgenerational influences exerted by maternal grandmothers, we developed breeding schemes where only the genotype of maternal grandmothers varied. HET females, to serve as MAT vs. MIX mothers, were generated, respectively, from WT × KO = MAT and MAT × KO = MIX breeding, with KO males acting as grandfather. The HET experimental groups, generated from either MAT or MIX mothers, were called MIX-by-MAT and MIX2 (male-fathers KO; asset-M: wild/healthy-allele from dam) or SOT and SIX (male-fathers WT; asset-P: mutated-allele from dam). Thus, sequelae of first encounter between wild/healthy and mutated DAT alleles (in maternal-lineage) were compared at first- (MAT-dam, WT-grandmother) vs. at second- (MIX-dam, HET-grandmother) generation. We characterized, within these epigenotypes, (1) circadian home-cage activity and (2) preference for social stimuli. Marked alterations of circadian activity appeared in MIX-by-MAT HETs, offspring of MAT-dams, compared with MIX2 HET (offspring of MIX-dams); The latter, in turn, were undistinguishable from WT-controls. A clear-cut social preference by WT rats was expressed towards SIX compared with SOT stimulus rats, confirming that the latter elicited reduced social motivations. In conclusion, significant epigenetic modulations took place in DAT-HET rats, as a function of maternal grandmother's genotype.

Keeping Track of the Genealogy of Heterozygotes Using Epigenetic Reference Codes and Breeding Tables.

Studying neurobehavioral consequences of the hypofunctional dopamine transporter (DAT) across several generations entails the need to monitor allelic transmission to offspring, taking into account both maternal and paternal inheritance. Since each type of heterozygote expresses differential phenotypes, based on lineage of inheritance for wild and mutated alleles (from male or female ancestors), it is important to track transgenerational epigenetic effects. We deemed it essential to assign specific abbreviations identifying their characteristics. Therefore, we devised a Mendelian-inspired table to keep track of these. Starting from two progenitors (WT and KO) we named resulting heterozygous progenies MAT and PAT to differentiate them based on inheritance of the wild allele (from the mother or father). Tracing subsequent generations, similar logic has been followed: if coupling HET dams with KO males, initials "M" [(grand)maternal] and "P" [(grand)paternal] are kept, but "AT" is turned into "IX" (MIX and PIX), while if breeding HETs with WTs, "M" is changed to "W" resembling an upside down "M" and "P" to "S" for "sperm" (WAT and SOT). To underline the development within "hyperdopaminergic-uterus" a central letter "U" is added (MUX, PUX, and QULL), while a Greek initial (µAT, µIX, and νIX) underlines the uterine-worsened origin of the allele. In HET × HET breeding (GIX and DIX), the mutated allele can be inherited from both sides of the genealogical line. However, when the mother is MAT, wild and mutated alleles encounter for the first time, causing putative anomalies in the progeny. Replacing dam with a second-generation female (MIX and MUX) may mitigate epigenetic effects on third-generation offspring; therefore suffixes ("-f," "-fu," "-ϕ," and "-ϕu") emphasize that subsequent-generation dams imply that the alleles already encountered in HET (rather than WT) grand-dams.