The breeding was carried out following both of two possible combinations: the first one in which the males were KO and the females were WT (from which we obtained a “maternal line” offspring, thus named MAT-HET) ( Zelli et al., 2021), and the other in which, instead, the males were WT and the females were KO (from which, therefore, a “paternal line” offspring was obtained, consequently named PAT-HET). Lately, it was decided to focus the observation specifically on heterozygous pups, obtained by breeding a knocked-out (KO) subject for the DAT gene and a wild-type (WT) one ( Adinolfi et al., 2019 Carbone et al., 2020). A classical type of heterozygous offspring was obtained by breeding parents that were both heterozygous for the DAT gene, and this led to a “mixed” offspring with Mendelian proportion of all genotypes, initially named, for this reason, MIX-HET. In our recent research work, we dealt with the study and observation on dopamine transporter (DAT) hypofunctional heterozygous rats. However, it could also be very useful to have simple genealogical tables at hand, allowing to obtain adequate information at “a glance.” For this purpose, some standardized cataloging protocols and specific guidelines are now available, such as the technical data sheets proposed by the Federation of European Laboratory Animal Science Association ( Bonaparte et al., 2013).
Such data should always include the correct name of the strain, detailed description of its characteristics, genetic/epi-genetic background, observed phenotypic and behavioral variations, etc. Therefore, it is essential to adequately monitor all relevant information related to various epigenetic features that could arise from: quality of maternal care, transgenerational transmission of the mutated allele by maternal, paternal or both lineages, up to fetal development within a hyperdopaminergic uterus (and consequent sequelae), and so on.
In such cases, a study on their genetic, phenotypic, and behavioral characteristics with an aim to discriminate paternal and/or maternal effects in offspring will obviously generate complexity and confusion. However, a need may arise to cross different phenotypes in order to obtain specific GA lines. To keep this simple, classical breeding may exploit heterozygous × heterozygous mating. 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.Īccurate genetic monitoring of laboratory colonies of genetically modified animal models (GA) should be an essential component of laboratory work and observations ( Benavides et al., 2020). However, when the mother is MAT, wild and mutated alleles encounter for the first time, causing putative anomalies in the progeny. In HET × HET breeding (GIX and DIX), the mutated allele can be inherited from both sides of the genealogical line. 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. Tracing subsequent generations, similar logic has been followed: if coupling HET dams with KO males, initials “M” and “P” 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). 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). Therefore, we devised a Mendelian-inspired table to keep track of these. We deemed it essential to assign specific abbreviations identifying their characteristics. 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. 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.
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