Unique food-entrained circadian rhythm in cysteine414-alanine mutant mCRY1 transgenic mice

Karyopherin Alpha 2-Expressing Pancreatic Duct Glands and Intra-Islet Ducts in Aged Diabetic C414A-Mutant-CRY1 Transgenic Mice

Our earlier studies demonstrated that cysteine414- (zinc-binding site of mCRY1-) alanine mutant mCRY1 transgenic mice (Tg mice) exhibit diabetes characterized by the reduction of β-cell proliferation and by β-cell dysfunction, presumably caused by senescence-associated secretory phenotype- (SASP-) like characters of islets. Earlier studies also showed that atypical duct-like structures in the pancreas developed age-dependently in Tg mice. Numerous reports have described that karyopherin alpha 2 (KPNA2) is highly expressed in cancers of different kinds. However, details of the expression of KPNA2 in pancreatic ductal atypia and in normal pancreatic tissues remain unclear. To assess the feature of the expression of KPNA2 in the development of the ductal atypia and islet architectures, we scrutinized the pancreas of Tg mice histopathologically. Results showed that considerable expression of KPNA2 was observed in pancreatic β-cells, suggesting its importance in maintaining the functions of β-cells. In mature stages, the level of KPNA2 expression was lower in islets of Tg mice than in wild-type controls. At 4 weeks, the expression levels of KPNA2 in islets of Tg mice were the same as those in wild-type controls. These results suggest that the reduction of KPNA2 might contribute to β-cell dysfunction in mature Tg mice. Additionally, the formation of mucin-producing intra-islet ducts, islet fibrosis, and massive T cell recruitment to the islet occurred in aged Tg mice. In exocrine areas, primary pancreatic intraepithelial neoplasias (PanINs) with mucinous pancreatic duct glands (PDGs) emerged in aged Tg mice. High expression of KPNA2 was observed in the ductal atypia. By contrast, KPNA2 expression in normal ducts was quite low. Thus, upregulation of KPNA2 seemed to be correlated with progression of the degree of atypia in pancreatic ductal cells. The SASP-like microenvironment inside islets might play stimulatory roles in the formation of ductal metaplasia inside islets and in islet fibrosis in Tg mice.

The Mysterious Food-Entrainable Oscillator: Insights from Mutant and Engineered Mouse Models

The food-entrainable oscillator (FEO) is a mysterious circadian clock because its anatomical location(s) and molecular timekeeping mechanism are unknown. Food anticipatory activity (FAA), which is defined as the output of the FEO, emerges during temporally restricted feeding. FAA disappears immediately during ad libitum feeding and reappears during subsequent fasting. A free-running FAA rhythm has been observed only in rare circumstances when food was provided with a period outside the range of entrainment. Therefore, it is difficult to study the circadian properties of the FEO. Numerous studies have attempted to identify the critical molecular components of the FEO using mutant and genetically engineered mouse models. Herein we critically review the experimental protocols and findings of these studies in mouse models. Several themes emerge from these studies. First, there is little consistency in restricted feeding protocols between studies. Moreover, the protocols were sometimes not optimal, resulting in erroneous conclusions that FAA was absent in some mouse models. Second, circadian genes are not necessary for FEO timekeeping. Thus, another noncanonical timekeeping mechanism must exist in the FEO. Third, studies of mouse models have shown that signaling pathways involved in circadian timekeeping, reward (dopaminergic), and feeding and energy homeostasis can modulate, but are not necessary for, the expression of FAA. In sum, the approaches to date have been largely unsuccessful in discovering the timekeeping mechanism of the FEO. Moving forward, we propose the use of standardized and optimized experimental protocols that focus on identifying genes that alter the period of FAA in mutant and engineered mouse models. This approach is likely to permit discovery of molecular components of the FEO timekeeping mechanism.

Unique Aspects of Cryptochrome in Chronobiology and Metabolism, Pancreatic β-Cell Dysfunction, and Regeneration: Research into Cysteine414-Alanine Mutant CRY1

Cryptochrome proteins (CRYs), which can bind noncovalently to cofactor (chromophore) flavin adenine dinucleotide (FAD), occur widely among organisms. CRYs play indispensable roles in the generation of circadian rhythm in mammals. Transgenic mice (Tg mice), ubiquitously expressing mouse CRY1 having a mutation in which cysteine414 (the zinc-binding site of CRY1) being replaced with alanine, display unique phenotypes in their circadian rhythms. Moreover, male Tg mice exhibit symptoms of diabetes characterized by beta-cell dysfunction, resembling human maturity onset diabetes of the young (MODY). The lowered proliferation of β-cells is a primary cause of age-dependent β-cell loss. Furthermore, unusually enlarged duct-like structures developed prominently in the Tg mice pancreases. The duct-like structures contained insulin-positive cells, suggesting neogenesis of β-cells in the Tg mice. This review, based mainly on the author's investigation of the unique features of Tg mice, presents reported results and recent findings related to molecular processes associated with mammalian cryptochromes, especially their involvement in the regulation of metabolism. New information is described with emphasis on the aspects of islet architecture, pancreatic β-cell dysfunction, and regeneration.