Paixao, T. | bioRxiv Science

bioRxiv2021

Phenotypic architecture of sociality and its associated genetic polymorphisms in zebrafish

Sociality is often seen as a single phenotypic trait, but it relies on motivational and cognitive components implemented by specific causal mechanisms. Hence, these components may have evolved independently, or may have been linked by phenotypic correlations driven by a shared selective pressure for increased social competence. Furthermore, these components may be domain-specific or of general domain across social and non-social contexts. Here we have characterized the phenotypic architecture of sociality in zebrafish, which has been increasingly used as a model organism in social neuroscience. For this purpose, we have behaviorally phenotyped zebrafish from different wild type lines in four tests: social tendency, social and non-social recognition, and open-field test. Our results indicate that: (1) sociality has two main components that are independent from each other (social tendency and social recognition), hence not supporting the occurrence of a sociality syndrome; (2) both social traits are phenotypically linked to non-social traits (non-social exploration and non-social memory, respectively), forming two general behavioral modules, general inspection and general recognition, and suggesting that sociality traits have been co-opted from general-domain motivational and cognitive traits. Moreover, the study of the association between genetic polymorphisms (i.e. single nucleotide polymorphisms, SNPs) and each behavioral module further supports this view, since several SNPs from a list of candidate "social" genes, are statistically associated with the general inspection (motivational), but not with a general recognition (cognitive), behavioral module. The SNPs associated with general inspection are widespread across different chromosomes and include neurotransmitters, neuromodulators, and synaptic plasticity genes, suggesting that this behavioral module is regulated by multiple genes, each of them with small effects. Together, these results support the occurrence of general domain motivational and cognitive behavioral modules in zebrafish, which have been co-opted for the social domain. Author summarySocial living has been considered one of the major transitions in evolution and it has been considered to act as a major selective force shaping the evolution of brain and behavior in animals. Sociality relies on two basic behavioral mechanisms: (1) the willingness to approach and be near others (aka social tendency); and (2) the ability to distinguish between others (aka social recognition) in order to adjust the behavior expressed during social interactions according to the identity of the interactant. There is an ongoing debate on to what extent these social abilities have specifically evolved in response to social living and are domain specific, or if they were selected as a broad response to cognitive demands and are of general domain. Here, we used zebrafish to test the domain-specific vs. general domain hypotheses and to assess the association of social tendency and social recognition with a set of candidate "social" genes (i.e. genes that have been linked to social behavior in other studies with different vertebrate species). We found that both social traits are not correlated to each other and are of general domain, and that only social tendency is associated with candidate "social" genes, suggesting that social tendency and social recognition are independent behavioral modules that rely on separate genetic architectures and that can evolve separately.

animal behavior and cognition↗

bioRxiv2021

Local genetic context shapes the function of a gene regulatory network

Gene expression levels are influenced by multiple coexisting molecular mechanisms. Some of these interactions, such as those of transcription factors and promoters have been studied extensively. However, predicting phenotypes of gene regulatory networks remains a major challenge. Here, we use a well-defined synthetic gene regulatory network to study how network phenotypes depend on local genetic context, i.e. the genetic neighborhood of a transcription factor and its relative position. We show that one gene regulatory network with fixed topology can display not only quantitatively but also qualitatively different phenotypes, depending solely on the local genetic context of its components. Our results demonstrate that changes in local genetic context can place a single transcriptional unit within two separate regulons without the need for complex regulatory sequences. We propose that relative order of individual transcriptional units, with its potential for combinatorial complexity, plays an important role in shaping phenotypes of gene regulatory networks.

molecular biology↗

bioRxiv2020

Self-renewal capacity of double negative 3 (DN3) early thymocytes preserves thymus autonomous function but compromises the β-selection checkpoint

T lymphocyte differentiation in the thymus relies on high cellular turnover, and cell competition enforces thymocyte replenishment. If deprived of competent progenitors, the thymus can maintain thymopoiesis autonomously for several weeks but this bears a high risk of leukemia. Here we show that double negative 3 early (DN3e) thymocytes can acquire stem cell like properties, which enables them to maintain thymopoiesis. Specifically, DN3e proved to be long-lived, they proliferated and differentiated in vivo, were necessary for autonomous thymopoiesis, and included DNA-label-retaining cells. Single cell RNAseq revealed a transcriptional program of thymopoiesis similar in autonomy and the controls. Nevertheless, a new population was identified in thymus autonomy that was enriched for an aberrant Notch target gene signature and bypassed the {beta}-selection checkpoint. In sum, DN3e have the potential to self-renew and differentiate in vivo if cell competition is compromised but this enables the accumulation of atypical cells, probably leading to leukemia.

immunology↗