The bioluminescent fish Parapriacanthus ransonneti does not synthesize the luciferase enzyme required for light emission; instead, it acquires the high-molecular-weight enzyme from its prey, the ostracod Cypridina noctiluca. This unique phenomenon, termed "kleptoprotein", represents a novel mode of phenotype acquisition where exogenous biopolymers are functionally sequestered. Unlike complex organelle sequestration (e.g., kleptoplasty), the kleptoprotein system involves a single protein, offering a tractable model to elucidate the molecular mechanisms of exogenous protein uptake. However, the mechanisms underlying luciferase internalization remain unknown due to the lack of tools to visualize and quantify this process. Here, we developed a dual-function probe by fusing the fluorescent protein Venus to C. noctiluca luciferase (VCL). Guided by AlphaFold 3 structural simulations predicting stable binding and catalytic integrity, we engineered a membrane-tethered Venus-trap system to validate VCL as a tracer. We demonstrate that VCL specifically interacts with the surface-displayed nanobody. Fluorescence imaging visualized VCL binding at trap-plasmid concentrations ≥ 50 ng/mL and VCL concentrations ≥ 2000 ng/mL. The bioluminescence assay exhibited superior sensitivity, detecting binding at VCL concentrations as low as 200 ng/mL. These results confirm that the fusion protein remains functionally intact and offers a highly sensitive detection method. This VCL-trap system establishes a robust platform for identifying the putative luciferase receptor and dissecting the intracellular dynamics of kleptoprotein bioluminescence.

Adipose tissue plays an important role in regulating body temperature and metabolism, with white adipocytes serving as storage units for energy. Recent research focused on the browning of white adipocytes (beige adipocytes), causing thermogenesis and lipolysis. The process of browning is linked to the activation of uncoupling protein (UCP) expression, which can be mediated by the β3 adrenergic receptor pathway. Transcriptional factors, such as peroxisome proliferator activated receptor γ (PPARγ) and PPARγ coactivator 1 alpha, play vital roles in cell fate determination for fat cells. Beige adipocytes have metabolic therapeutic potential to combat diseases such as obesity, diabetes mellitus, and dyslipidemia, owing to their significant impact on metabolic functions. However, the molecular mechanisms that cause the induction of browning are unclear. Therefore, research using animal models and primary culture is essential to provide an understanding of browning for further application in human metabolic studies. Pigs have physiological similarities to humans; hence, they are valuable models for research on adipose tissue. This study demonstrates the browning potential of pig white adipocytes through primary culture experiments. The results show that upregulation of UCP3 gene expression and fragmentation of lipid droplets into smaller particles occur due to isoproterenol stimulation, which activates beta-adrenergic receptor signaling. Furthermore, PPARγ and PGC-1α were found to activate the UCP3 promoter region, similar to that of UCP1. These findings suggest that pigs undergo metabolic changes that induce browning in white adipocytes, providing a promising approach for metabolic research with potential implications for human health. This study offers valuable insights into the mechanism of adipocyte browning using pig primary culture that can enhance our understanding of human metabolism, leading to cures for commonly occurring diseases.

In this study, we examined the morphological features of the placentas from 3 species of rorqual whales (Balaenopteridae), namely Bryde's (Balaenoptera brydei), sei (B. borealis), and common minke (B. acutorostrata) whales, and verified the secretion of 2 placental-specific peptide hormones, placental lactogen (PL) and chorionic gonadotropin (CG). The placentas were collected in the second phase of the Japanese Whale Research Program under a special permit in the North Pacific (JARPN II) between 2009 and 2010. For all three species of rorqual whales, as the fetus grew, the interdigitation between the maternal endometrial folds and chorionic villi became more complicated, and many blood capillaries of chorionic villi and endometrium became larger and infiltrated the trophoblast cells and endometrial epithelial cells, respectively. In the immunohistochemical examination, the trophoblast cells (except for areolar trophoblast cells) showed immunoreactivities for the PL and luteinizing hormone (LH) antibodies, and this phenomenon was similar in the placentas of all 3 rorqual whale species. Our results suggest that PL and LH-like CG play roles in regulating pregnancy in the placenta of cetacean.