Abstract
Successful sexual reproduction involves complex, genetically encoded interplay between animal physiology and behavior. The rat provides a highly fecund mammalian model for studying how the brain impacts reproduction. Here, we report a forward genetics screen in rats to identify genes that affect reproduction. A panel of 18 distinct rat strains harboring Sleeping Beauty gene trap mutations were analyzed for the ability to reproduce. As expected, our mutant screen identified genes where reproductive failure was connected to gametogenesis (Btrc, Pan3, Spaca6, Ube2k) and embryogenesis (Alk3, Exoc6b, Slc1a3, Tmx4, Zmynd8). In addition, we identified Ata13 (longevity) and Pclo (neuronal disorders), previously not associated with an inability to conceive. Neurologically, Pclo is known to regulate the size of presynaptic vesicle pools. Here, dominant traits in Pclo mutant rats caused epileptiform activity and affected genes supporting GABAergic synaptic transmission (Gabra6, Gabrg3). Recessive traits in Pclo mutant rats transmitted altered reproductive behavior, as homozygous Pclo mutant rats produced gametes but neither sex would mate with wildtype rats. Pclo mutant rat behavior was linked to endophenotypes signifying compromised brain-gonad crosstalk via disturbed GnRH signaling and allelic markers for major depressive disorder in humans (Grm5, Htr2a, Sorcs3, Negr1, Drd2). Thus, by rat genetics, we identified Pclo as a candidate presynaptic factor required for reproduction.
Author Summary Piccolo gene mutations have previously been identified in human cohorts diagnosed with behavioral syndromes that impact one’s emotions, including depression and bipolar disorder. Although studies in human populations implicate changes to Piccolo’s DNA sequence to enhanced susceptibility for behavioral disorders, studies in mouse models have yet to link Piccolo mutations to altered behavior. Here, by a novel genetics approach, we report Piccolo mutation-dependent effects on reproductive behavior in rats, a finding that may turn out to be relevant to the behavioral effects that are associated with human Piccolo gene mutations. Thus, research aimed at understanding how Piccolo functions to regulate reproduction in rats could prove pivotal in our ability to understand neurological mechanisms that influence human emotions.
Footnotes
Our work demonstrates the feasibility and the robustness ofconducting forward genetics in rats and highlights the benefits of expanding research on disease-related genes into relatively untapped genetic architecture transmitted by alternate mammalian models (eg other than mice). Thus, our study demonstrates the power of an unbiased approach versus a targeted approach in the rat model and how it led us to identify unanticipated genetic associations between various biological processes (eg link between Pclo, sexual motivation, aggression and depression). Surprisingly, our study demonstrates robust phenotypical differences between animal models (eg rat and mouse). Based on our work here, future studies can now be aimed at moving the behavioral and reproductive science fields forward by defining Pclo-dependent neural circuits in the rat that control social behavior, and prospectively, how Pclo-dependent neuroendocrine signaling integrates social responses with an individual's physiological state. Relationship to current literature on the topic. Following on the premise that sexual reproduction is neurologically coupled to complex human social interactions, we continued our focus on the Pclo knockout. Revised manuscript contains following new informations: is not able to reproduce unlike Pclo knockout mice is not impaired in gametogenesis, but serves a behavioralmodel of infertility develops generalized seizures, similarly to children with Pclo-variants that cause cerebellar hypoplasia models heritable Piccolo-linked neuropathies (both dominantand recessive) reveals that while no significant change of Pclo (RNA/protein)levels are detectable in heterozygous rats, 60% of the differentially expressed genes (DEGs) are shared between homo- andheterozygous animals, suggesting strong allelic regulatory effect byPclo reveals a dominant epileptiform activity and affected genes supporting GABAergic synaptic transmission (Gabra6, Gabrg3) indominant Pclo traits identify a Pclo-dependent GABAergic cross-talk between brain and gonad via GnRH signaling (not reported in Gabra6 knockouts)decipher that while GnRH neurons reach the hypothalamus in normal numbers (maturation) in Pclo rats, several components of the GnRH signaling cascade are down-regulated uncover that as a result of the disrupted GnRH signaling, the reduced level of gonadotropins (FSH, LH) and testosterone are notable to properly activate their target genes in the testis of Pclo rats;indicate that recessive Pclo traits disrupt con specific recognition required for courtship/mating and to properly regulate aggression reveal a transcriptome-wide similarity with a depression rat model (pituitary and hypothalamus) reveal that recessive Pclo traits are mappable to allelic markers for major depressive disorder (MDD).