Venom trade-off shapes interspecific interactions, physiology, and reproduction.

The ability of an animal to effectively capture prey and defend against predators is pivotal for survival. Venom is often a mixture of many components including toxin proteins that shape predator-prey interactions. Here, we used the sea anemone Nematostella vectensis to test the impact of toxin genotypes on predator-prey interactions. We developed a genetic manipulation technique to demonstrate that both transgenically deficient and a native Nematostella strain lacking a major neurotoxin (Nv1) have a reduced ability to defend themselves against grass shrimp, a native predator. In addition, secreted Nv1 can act indirectly in defense by attracting mummichog fish, which prey on grass shrimp. Here, we provide evidence at the molecular level of an animal-specific tritrophic interaction between a prey, its antagonist, and a predator. Last, this study reveals an evolutionary trade-off, as the reduction of Nv1 levels allows for faster growth and increased reproductive rates.

Tsh Induces Agrp1 Neuron Proliferation in Oatp1c1-Deficient Zebrafish.

Thyroid hormones (THs), thyroxine (T4), and triiodothyronine (T3), regulate growth, metabolism, and neurodevelopment. THs secretion is controlled by the pituitary thyroid-stimulating hormone (TSH) and the hypothalamic-pituitary-thyroid (HPT) axis. The organic anion-transporting polypeptide 1C1 (OATP1C1/SLCO1C1) and the monocarboxylate transporter 8 (MCT8/SLC16A2) actively transport THs, which bind to their nuclear receptors and induce gene expression. A mutation in OATP1C1 is associated with brain hypometabolism, gradual neurodegeneration, and impaired cognitive and motor functioning in adolescent patients. To understand the role of Oatp1c1 and the mechanisms of the disease, we profiled the transcriptome of oatp1c1 mutant (oatp1c1 -/-) and mct8 -/- xoatp1c1 -/- adult male and female zebrafish brains. Among dozens of differentially expressed genes, agouti-related neuropeptide 1 (agrp1) expression increased in oatp1c1 -/- adult brains. Imaging in the hypothalamus revealed enhanced proliferation of Agrp1 neurons in oatp1c1 -/- larvae and adults, and increased food consumption in oatp1c1 -/- larvae. Similarly, feeding and the number of Agrp1 neurons increased in thyroid gland-ablated zebrafish. Pharmacological treatments showed that the T3 analog TRIAC (3,3',5-tri-iodothyroacetic acid), but not T4, normalized the number of Agrp1 neurons in oatp1c1 -/- zebrafish. Since the HPT axis is hyperactive in the oatp1c1 -/- brain, we used the CRISPR-Cas9 system to knockdown tsh in oatp1c1 -/- larvae, and inducibly enhanced the HPT axis in wild-type larvae. These manipulations showed that Tsh promotes proliferation of Agrp1 neurons and increases food consumption in zebrafish. The results revealed upregulation of both the HPT axis-Agrp1 circuitry and feeding in a zebrafish model for OATP1C1 deficiency.SIGNIFICANCE STATEMENT Mutation in the thyroid hormone (TH) transporter OATP1C1 is associated with cognitive and motor functioning disturbances in humans. Here, we used an oatp1c1 -/- zebrafish to understand the role of organic anion-transporting polypeptide 1C1 (Oatp1c1), and the characteristics of OATP1C1 deficiency. Transcriptome profiling identified upregulation of agrp1 expression in the oatp1c1 -/- brain. The oatp1c1 -/- larvae showed increased thyroid-stimulating hormone (tsh) levels, proliferation of Agrp1 neurons and food consumption. Genetic manipulations of the hypothalamic-pituitary-thyroid (HPT) axis showed that Tsh increases the number of Agrp1 neurons and food consumption. The T3 analog TRIAC (3,3',5-tri-iodothyroacetic acid) normalizes the number of Agrp1 neurons and may have potential for the treatment of Oatp1c1 deficiency. The findings demonstrate a functional interaction between the thyroid and feeding systems in the brain of zebrafish and suggest a neuroendocrinological mechanism for OATP1C1 deficiency.

Structure-Function Analysis of the Drosophila melanogaster Caudal Transcription Factor Provides Insights into Core Promoter-preferential Activation.

Regulation of RNA polymerase II transcription is critical for the proper development, differentiation, and growth of an organism. The RNA polymerase II core promoter is the ultimate target of a multitude of transcription factors that control transcription initiation. Core promoters encompass the RNA start site and consist of functional elements such as the TATA box, initiator, and downstream core promoter element (DPE), which confer specific properties to the core promoter. We have previously discovered that Drosophila Caudal, which is a master regulator of genes involved in development and differentiation, is a DPE-specific transcriptional activator. Here, we show that the mouse Caudal-related homeobox (Cdx) proteins (mCdx1, mCdx2, and mCdx4) are also preferential core promoter transcriptional activators. To elucidate the mechanism that enables Caudal to preferentially activate DPE transcription, we performed structure-function analysis. Using a systematic series of deletion mutants (all containing the intact DNA-binding homeodomain) we discovered that the C-terminal region of Caudal contributes to the preferential activation of the fushi tarazu (ftz) Caudal target gene. Furthermore, the region containing both the homeodomain and the C terminus of Caudal was sufficient to confer core promoter-preferential activation to the heterologous GAL4 DNA-binding domain. Importantly, we discovered that Drosophila CREB-binding protein (dCBP) is a co-activator for Caudal-regulated activation of ftz. Strikingly, dCBP conferred the ability to preferentially activate the DPE-dependent ftz reporter to mini-Caudal proteins that were unable to preferentially activate ftz transcription themselves. Taken together, it is the unique combination of dCBP and Caudal that enables the co-activation of ftz in a core promoter-preferential manner.