👤 Simon Yung Wa Sin

High-sugar diets cause human metabolic diseases, yet several bird lineages convergently adapted to feeding on sugar-rich nectar or fruits. We investigated the underlying molecular mechanisms in hummingbirds, parrots, honeyeaters, and sunbirds by generating nine new genomes and 90 tissue-specific transcriptomes. Comparative screens revealed an excess of repeated selection in both protein-coding and regulatory sequences in sugar-feeding birds, suggesting reuse of genetic elements. Sequence or expression changes in sugar-feeders affect genes involved in blood pressure regulation and lipid, amino acid, and carbohydrate metabolism, with experiments showing functional changes in honeyeater hexokinase 3. Show less

By various assessments, the previous study has unequivocally concluded functional apoB and MTTP (microsomal triglyceride transfer protein) for VLDL production in chicken ovaries. The present study sought to use whole tissue culture to define the role of VLDL secretion by small yellow follicles (SYFs) along their development under normal and heat stress (HS) conditions. Under thermoneutral conditions (39 °C), chicken SYFs increased MTTP activity, apoB expression and VLDL secretion, while underwent cell apoptosis along the time course. Despite relieved ER stress and protein ubiquitinylation, inhibition of VLDL secretion by Lomitapide and Mipomersen greatly increased triglyceride accumulation, impaired estradiol production and cell proliferation, and accelerated cell apoptosis in accordance with upregulated caspase 3/7 activity, JNK activation, protein carbonylation, and MDA accumulation. Exposure to HS at 44 °C boosted cell apoptosis in a duration-dependent manner. Acute HS for 3 h enhanced VLDL secretion, impaired estradiol production and cell proliferation, and promoted IL-1b production, oxidative damages, and cell apoptosis, whereas except MDA content and cell proliferation, the detrimental effects were halted after 13 h recovery. Lomitapide and Mipomersen augmented lipid accumulation, oxidative stress, inflammatory response, and exacerbated transient impairment of estradiol secretion and cell proliferation in SYFs under 3 h HS and after recovery, but failed to rescue cell viability despite relieved ER and proteostatic stress. In conclusion, routine secretion of VLDL by SYFs serves as an intrinsic mechanism to sustain cell viability and functions to support the whole program required for follicle development, while under HS, this mechanism provisionally rescues steroidogenesis and cell proliferation. Show less

Lipids are a principal component of drusen and are involved in the pathobiology of age-related macular degeneration (AMD). Nonhuman primates (NHPs) develop macular drusen and may provide insight into circulating or local lipids in AMD. We evaluated aged rhesus macaques by fundus photography, optical coherence tomography (OCT), and fundus autofluorescence, as well as measured fasting plasma glucose, total cholesterol, high- and low-density lipoproteins, triglycerides, and apolipoprotein (Apo) A1, B, CIII, and E. Retinal tissues were collected for electron microscopy and immunostained for oil red O, ApoE, and ApoB. Among 203 adult macaques (mean age 19.1 ± 3.1 years), 25 animals (12.1%) exhibited soft drusen with sub-RPE deposits, while 59 (28.6%) had yellow punctate dots that were mostly hyperautofluorescent without RPE elevation on OCT. Drusen prevalence increased with older age (P = 0.001) but not with plasma lipids (P > 0.05 for all), while the punctate dot phenotype was associated with older age (P = 0.014), higher fasting glucose (P = 0.023), low-density lipoprotein cholesterol (P = 0.022), and ApoB (P = 0.017). Ultrastructure revealed NHP drusen consisting of extracellular sub-RPE lipid particles, whereas punctate dots appeared to correspond to individual RPE cells with intracellular lipid vacuoles. Both sub-RPE and intra-RPE lipids of the two phenotypes contained neutral lipids and ApoE, while ApoE and ApoB appeared to be expressed in RPE. In rhesus macaques, soft drusen are extracellular lipid deposits associated with older age, while punctate dots are intracellular lipids linked to age, hyperglycemia, and hyperlipidemia, suggesting differential dysregulation of lipid transport in these NHP models of AMD. Show less

In mammals, tissues other than liver and intestine are known to possess functional MTTP (microsomal triglyceride transfer protein) and apoB (apolipoprotein B) capable of VLDL (very low-density lipoprotein) assembly. Birds are oviparous and possess unique capabilities in lipid biology to accommodate yolk formation through massive deposition of hepatically assembled yolk-targeted VLDLy into ovarian follicles. Following identifications of MTTP and ApoB expression within chicken ovarian stroma, granulosa, theca, and epithelial cells of various classes of follicles, we sought to define the functionality of ovarian MTTP and ApoB in VLDL assembly. In situ hybridization analysis found that ApoB transcripts are most abundant in thecal layers, whereas immunohistochemistry showed that MTTP predominates in the granulosa layers. MTTP lipid transfer activity was greater in small yellow follicles than in hierarchical follicles. Metabolic labeling, electron microscopy, and Western blot studies confirmed the functionality of ovarian apoB and MTTP as newly assembled VLDL around 50-200 nm in diameter and lacking ApoVLDL-II dissimilar to VLDLy, were secreted from cultured follicular cells. Lomitapide and the ApoB-antisense oligonucleotide Mipomersen dose-dependently decreased MTTP activity and VLDL-apoB secretion from cultured follicular cells, while oleate addition or acute heat stress enhanced VLDL-apoB secretion. Ultrastructural images showed VLDL assembly and trafficking toward the secretion route. The findings support the notion that VLDL assembly and secretion within avian ovarian tissues functions as a protective mechanism against fuel and physical stressors to secure follicle development and/or nutritional quality control of yolk for embryo development. Show less

Sex chromosome inactivation is essential epigenetic programming in male germ cells. However, it remains largely unclear how epigenetic silencing of sex chromosomes impacts the evolution of the mammalian genome. Here we demonstrate that male sex chromosome inactivation is highly conserved between humans and mice and has an impact on the genetic evolution of human sex chromosomes. We show that, in humans, sex chromosome inactivation established during meiosis is maintained into spermatids with the silent compartment postmeiotic sex chromatin (PMSC). Human PMSC is illuminated with epigenetic modifications such as trimethylated lysine 9 of histone H3 and heterochromatin proteins CBX1 and CBX3, which implicate a conserved mechanism underlying the maintenance of sex chromosome inactivation in mammals. Furthermore, our analyses suggest that male sex chromosome inactivation has impacted multiple aspects of the evolutionary history of mammalian sex chromosomes: amplification of copy number, retrotranspositions, acquisition of de novo genes, and acquisition of different expression profiles. Most strikingly, profiles of escape genes from postmeiotic silencing diverge significantly between humans and mice. Escape genes exhibit higher rates of amino acid changes compared with non-escape genes, suggesting that they are beneficial for reproductive fitness and may allow mammals to cope with conserved postmeiotic silencing during the evolutionary past. Taken together, we propose that the epigenetic silencing mechanism impacts the genetic evolution of sex chromosomes and contributed to speciation and reproductive diversity in mammals. Show less