Propionic acid induces alterations in mitochondrial morphology and dynamics in SH-SY5Y cells.

Propionic acid (PPA) is used to study the role of mitochondrial dysfunction in neurodevelopmental conditions like autism spectrum disorders. PPA is known to disrupt mitochondrial biogenesis, metabolism, and turnover. However, the effect of PPA on mitochondrial dynamics, fission, and fusion remains challenging to study due to the complex temporal nature of these mechanisms. Here, we use complementary quantitative visualization techniques to examine how PPA influences mitochondrial ultrastructure, morphology, and dynamics in neuronal-like SH-SY5Y cells. PPA (5 mM) induced a significant decrease in mitochondrial area (p < 0.01), Feret's diameter and perimeter (p < 0.05), and in area2 (p < 0.01). Mitochondrial event localiser analysis demonstrated a significant increase in fission and fusion events (p < 0.05) that preserved mitochondrial network integrity under stress. Moreover, mRNA expression of cMYC (p < 0.0001), NRF1 (p < 0.01), TFAM (p < 0.05), STOML2 (p < 0.0001), and OPA1 (p < 0.01) was significantly decreased. This illustrates a remodeling of mitochondrial morphology, biogenesis, and dynamics to preserve function under stress. Our data provide new insights into the influence of PPA on mitochondrial dynamics and highlight the utility of visualization techniques to study the complex regulatory mechanisms involved in the mitochondrial stress response.

A molecular framework for autistic experiences: Mitochondrial allostatic load as a mediator between autism and psychopathology.

Molecular autism research is evolving toward a biopsychosocial framework that is more informed by autistic experiences. In this context, research aims are moving away from correcting external autistic behaviors and toward alleviating internal distress. Autism Spectrum Conditions (ASCs) are associated with high rates of depression, suicidality and other comorbid psychopathologies, but this relationship is poorly understood. Here, we integrate emerging characterizations of internal autistic experiences within a molecular framework to yield insight into the prevalence of psychopathology in ASC. We demonstrate that descriptions of social camouflaging and autistic burnout resonate closely with the accepted definitions for early life stress (ELS) and chronic adolescent stress (CAS). We propose that social camouflaging could be considered a distinct form of CAS that contributes to allostatic overload, culminating in a pathophysiological state that is experienced as autistic burnout. Autistic burnout is thought to contribute to psychopathology via psychological and physiological mechanisms, but these remain largely unexplored by molecular researchers. Building on converging fields in molecular neuroscience, we discuss the substantial evidence implicating mitochondrial dysfunction in ASC to propose a novel role for mitochondrial allostatic load in the relationship between autism and psychopathology. An interplay between mitochondrial, neuroimmune and neuroendocrine signaling is increasingly implicated in stress-related psychopathologies, and these molecular players are also associated with neurodevelopmental, neurophysiological and neurochemical aspects of ASC. Together, this suggests an increased exposure and underlying molecular susceptibility to ELS that increases the risk of psychopathology in ASC. This article describes an integrative framework shaped by autistic experiences that highlights novel avenues for molecular research into mechanisms that directly affect the quality of life and wellbeing of autistic individuals. Moreover, this framework emphasizes the need for increased access to diagnoses, accommodations, and resources to improve mental health outcomes in autism.

Convergent Canonical Pathways in Autism Spectrum Disorder from Proteomic, Transcriptomic and DNA Methylation Data.

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder with extensive genetic and aetiological heterogeneity. While the underlying molecular mechanisms involved remain unclear, significant progress has been facilitated by recent advances in high-throughput transcriptomic, epigenomic and proteomic technologies. Here, we review recently published ASD proteomic data and compare proteomic functional enrichment signatures with those of transcriptomic and epigenomic data. We identify canonical pathways that are consistently implicated in ASD molecular data and find an enrichment of pathways involved in mitochondrial metabolism and neurogenesis. We identify a subset of differentially expressed proteins that are supported by ASD transcriptomic and DNA methylation data. Furthermore, these differentially expressed proteins are enriched for disease phenotype pathways associated with ASD aetiology. These proteins converge on protein-protein interaction networks that regulate cell proliferation and differentiation, metabolism, and inflammation, which demonstrates a link between canonical pathways, biological processes and the ASD phenotype. This review highlights how proteomics can uncover potential molecular mechanisms to explain a link between mitochondrial dysfunction and neurodevelopmental pathology.

DNA Methylation of PGC-1α Is Associated With Elevated mtDNA Copy Number and Altered Urinary Metabolites in Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is a complex disorder that is underpinned by numerous dysregulated biological pathways, including pathways that affect mitochondrial function. Epigenetic mechanisms contribute to this dysregulation and DNA methylation is an important factor in the etiology of ASD. We measured DNA methylation of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α), as well as five genes involved in regulating mitochondrial homeostasis to examine mitochondrial dysfunction in an ASD cohort of South African children. Using targeted Next Generation bisulfite sequencing, we found differential methylation (p < 0.05) at six key genes converging on mitochondrial biogenesis, fission and fusion in ASD, namely PGC-1α, STOML2, MFN2, FIS1, OPA1, and GABPA. PGC-1α, the transcriptional regulator of biogenesis, was significantly hypermethylated at eight CpG sites in the gene promoter, one of which contained a putative binding site for CAMP response binding element 1 (CREB1) (p = 1 × 10-6). Mitochondrial DNA (mtDNA) copy number, a marker of mitochondrial function, was elevated (p = 0.002) in ASD compared to controls and correlated significantly with DNA methylation at the PGC-1α promoter and there was a positive correlation between methylation at PGC-1α CpG#1 and mtDNA copy number (Spearman's r = 0.2, n = 49, p = 0.04) in ASD. Furthermore, DNA methylation at PGC-1α CpG#1 and mtDNA copy number correlated significantly (p < 0.05) with levels of urinary organic acids associated with mitochondrial dysfunction, oxidative stress, and neuroendocrinology. Our data show differential methylation in ASD at six key genes converging on PGC-1α-dependent regulation of mitochondrial biogenesis and function. We demonstrate that methylation at the PGC-1α promoter is associated with elevated mtDNA copy number and metabolomic evidence of mitochondrial dysfunction in ASD. This highlights an unexplored role for DNA methylation in regulating specific pathways involved in mitochondrial biogenesis, fission and fusion contributing to mitochondrial dysfunction in ASD.

DNA Methylation Associated with Mitochondrial Dysfunction in a South African Autism Spectrum Disorder Cohort.

Autism spectrum disorder (ASD) is characterized by phenotypic heterogeneity and a complex genetic architecture which includes distinctive epigenetic patterns. We report differential DNA methylation patterns associated with ASD in South African children. An exploratory whole-epigenome methylation screen using the Illumina 450 K MethylationArray identified differentially methylated CpG sites between ASD and controls that mapped to 898 genes (P ≤ 0.05) which were enriched for nine canonical pathways converging on mitochondrial metabolism and protein ubiquitination. Targeted Next Generation Bisulfite Sequencing of 27 genes confirmed differential methylation between ASD and control in our cohort. DNA pyrosequencing of two of these genes, the mitochondrial enzyme Propionyl-CoA Carboxylase subunit Beta (PCCB) and Protocadherin Alpha 12 (PCDHA12), revealed a wide range of methylation levels (9-49% and 0-54%, respectively) in both ASD and controls. Three CpG loci were differentially methylated in PCCB (P ≤ 0.05), while PCDHA12, previously linked to ASD, had two significantly different CpG sites (P ≤ 0.001) between ASD and control. Differentially methylated CpGs were hypomethylated in ASD. Metabolomic analysis of urinary organic acids revealed that three metabolites, 3-hydroxy-3-methylglutaric acid (P = 0.008), 3-methyglutaconic acid (P = 0.018), and ethylmalonic acid (P = 0.043) were significantly elevated in individuals with ASD. These metabolites are directly linked to mitochondrial respiratory chain disorders, with a putative link to PCCB, consistent with impaired mitochondrial function. Our data support an association between DNA methylation and mitochondrial dysfunction in the etiology of ASD. Autism Res 2020, 13: 1079-1093. © 2020 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc. LAY SUMMARY: Epigenetic changes are chemical modifications of DNA which can change gene function. DNA methylation, a type of epigenetic modification, is linked to autism. We examined DNA methylation in South African children with autism and identified mitochondrial genes associated with autism. Mitochondria are power-suppliers in cells and mitochondrial genes are essential to metabolism and energy production, which are important for brain cells during development. Our findings suggest that some individuals with ASD also have mitochondrial dysfunction.

Genetic signatures for enhanced olfaction in the African mole-rats.

The Olfactory Receptor (OR) superfamily, the largest in the vertebrate genome, is responsible for vertebrate olfaction and is traditionally subdivided into 17 OR families. Recent studies characterising whole-OR subgenomes revealed a 'birth and death' model of evolution for a range of species, however little is known about fine-scale evolutionary dynamics within single-OR families. This study reports the first assessment of fine-scale OR evolution and variation in African mole-rats (Bathyergidae), a family of subterranean rodents endemic to sub-Saharan Africa. Because of the selective pressures of life underground, enhanced olfaction is proposed to be fundamental to the evolutionary success of the Bathyergidae, resulting in a highly diversified OR gene-repertoire. Using a PCR-sequencing approach, we analysed variation in the OR7 family across 14 extant bathyergid species, which revealed enhanced levels of functional polymorphisms concentrated across the receptors' ligand-binding region. We propose that mole-rats are able to recognise a broad range of odorants and that this diversity is reflected throughout their OR7 gene repertoire. Using both classic tests and tree-based methods to test for signals of selection, we investigate evolutionary forces across the mole-rat OR7 gene tree. Four well-supported clades emerged in the OR phylogeny, with varying signals of selection; from neutrality to positive and purifying selection. Bathyergid life-history traits and environmental niche-specialisation are explored as possible drivers of adaptive OR evolution, emerging as non-exclusive contributors to the positive selection observed at OR7 genes. Our results reveal unexpected complexity of evolutionary mechanisms acting within a single OR family, providing insightful perspectives into OR evolutionary dynamics.

Variability in kidney stone incidence between black and white South Africans: AGT Pro11Leu polymorphism is not a factor.

BACKGROUND AND PURPOSE: Kidney stone disease is rare in the South African black (B) population and more prevalent in the white (W) population. Genetic studies have not previously examined this anomaly. The AGT Pro11Leu polymorphism in the alanine:glyoxylate aminotransferase (AGT) enzyme has been suggested as possibly playing a role in the pathogenesis of idiopathic calcium oxalate kidney stones. The present study was undertaken to investigate whether differences occur in the frequency of this polymorphism in subjects of both race groups. MATERIALS AND METHODS: Healthy B (n=60) and W (n=60) male subjects each provided early morning spot urine, blood, and buccal cell samples. The AGT Pro11Leu locus was amplified using the polymerase chain reaction and polymorphism was genotyped using a restriction fragment length polymorphism. RESULTS: There was no difference in the frequency of the AGT Pro11Leu polymorphism, and the major allele (C) was present at a frequency of 0.82 in B and 0.83 in W. Thus, the most common genotype homozygous normal CC genotype was observed at similar frequencies in both groups (0.68 and 0.65 in B and W, respectively), as were the heterozygous CT genotype (CT) and the homozygous variant TT genotype (TT) genotypes (0.33 & 0.02 and 0.28 & 0.03 in B and W, respectively). Neither urinary oxalate nor any other component in the two groups was correlated with the frequency of the AGT Pro11Leu polymorphism. CONCLUSIONS: Our data imply that the AGT Pro11Leu polymorphism is not directly responsible for the low incidence of stone formation in B. We conclude that other factors must be instrumental in protecting the B population from urolithiasis.

Costly reproductive competition between females in a monogamous cooperatively breeding bird.

In many cooperatively breeding societies, only a few socially dominant individuals in a group breed, reproductive skew is high, and reproductive conflict is common. Surprisingly, the effects of this conflict on dominant reproductive success in vertebrate societies have rarely been investigated, especially in high-skew societies. We examine how subordinate female competition for breeding opportunities affects the reproductive success of dominant females in a monogamous cooperatively breeding bird, the Southern pied babbler (Turdoides bicolor). In this species, successful subordinate reproduction is very rare, despite the fact that groups commonly contain sexually mature female subordinates that could mate with unrelated group males. However, we show that subordinate females compete with dominant females to breed, and do so far more often than expected, based on the infrequency of their success. Attempts by subordinates to obtain a share of breeding impose significant costs on dominant females: chicks fledge from fewer nests, more nests are abandoned before incubation begins, and more eggs are lost. Dominant females appear to attempt to reduce these costs by aggressively suppressing potentially competitive subordinate females. This empirical evidence provides rare insight into the nature of the conflicts between females and the resultant costs to reproductive success in cooperatively breeding societies.

Inbreeding avoidance mechanisms: dispersal dynamics in cooperatively breeding southern pied babblers.

1. Breeding with kin can reduce individual fitness through the deleterious effects of inbreeding depression. Inbreeding avoidance mechanisms are expected to have developed in most species, and especially in cooperatively breeding species where individuals may delay dispersal until long after sexual maturity. Such potential mechanisms include sex-biased dispersal and avoidance of kin known through associative learning. 2. The investigation of inbreeding avoidance through dispersal dynamics can be enhanced by combining fine-scale population genetic structure data with detailed behavioural observations of wild populations. 3. We investigate possible inbreeding avoidance in a wild population of cooperatively breeding southern pied babblers (Turdoides bicolor). A combination of genetic, geographic and observational data is used to examine fine-scale genetic structure, dispersal (including sex-biased dispersal) and inheritance of dominance in cooperatively breeding groups. 4. Unusually, sex-bias in dispersal distance does not occur. Rather, individuals appear to avoid inbreeding through two routes. First, through dispersal itself: although both males and females disperse locally, they move outside the range within which genetically similar individuals are usually found, going twice as far from natal groups as from non-natal groups. Second, through avoidance of familiar group members as mates: individuals inherit a dominant position in the natal group only when an unrelated breeding partner is present. 5. This study uses spatial genetic analyses to investigate inbreeding avoidance mechanisms in a cooperative breeder and shows that individuals of both sexes can avoid inbreeding through a dispersal distance mechanism. While it appears that dispersal allows most individuals to move beyond the range of closely related kin, matings may still occur between distant kin. Nevertheless, any costs of breeding with a distant relative may be outweighed by the benefits of local dispersal and the immense fitness gains available from attaining a breeding position.

Cryptic diversity of African tigerfish (genus Hydrocynus) reveals palaeogeographic signatures of linked neogene geotectonic events.

The geobiotic history of landscapes can exhibit controls by tectonics over biotic evolution. This causal relationship positions ecologically specialized species as biotic indicators to decipher details of landscape evolution. Phylogeographic statistics that reconstruct spatio-temporal details of evolutionary histories of aquatic species, including fishes, can reveal key events of drainage evolution, notably where geochronological resolution is insufficient. Where geochronological resolution is insufficient, phylogeographic statistics that reconstruct spatio-temporal details of evolutionary histories of aquatic species, notably fishes, can reveal key events of drainage evolution. This study evaluates paleo-environmental causes of mitochondrial DNA (mtDNA) based phylogeographic records of tigerfishes, genus Hydrocynus, in order to reconstruct their evolutionary history in relation to landscape evolution across Africa. Strong geographical structuring in a cytochrome b (cyt-b) gene phylogeny confirms the established morphological diversity of Hydrocynus and reveals the existence of five previously unknown lineages, with Hydrocynus tanzaniae sister to a clade comprising three previously unknown lineages (Groups B, C and D) and H. vittatus. The dated phylogeny constrains the principal cladogenic events that have structured Hydrocynus diversity from the late Miocene to the Plio-Pleistocene (ca. 0-16 Ma). Phylogeographic tests reveal that the diversity and distribution of Hydrocynus reflects a complex history of vicariance and dispersals, whereby range expansions in particular species testify to changes to drainage basins. Principal divergence events in Hydrocynus have interfaced closely with evolving drainage systems across tropical Africa. Tigerfish evolution is attributed to dominant control by pulses of geotectonism across the African plate. Phylogenetic relationships and divergence estimates among the ten mtDNA lineages illustrates where and when local tectonic events modified Africa's Neogene drainage. Haplotypes shared amongst extant Hydrocynus populations across northern Africa testify to recent dispersals that were facilitated by late Neogene connections across the Nilo-Sahelian drainage. These events in tigerfish evolution concur broadly with available geological evidence and reveal prominent control by the African Rift System, evident in the formative events archived in phylogeographic records of tigerfish.

Phylogeography and taxonomy of White-chinned and Spectacled Petrels.

The genus Procellaria traditionally consists of four species, two restricted to New Zealand and two widespread in the Southern Ocean. All four are threatened because of incidental mortality on longlines and other fishing gear. The White-chinned Petrel P. aequinoctialis is the seabird killed in largest numbers by fisheries in the Southern Ocean. A spectacled form recently has been elevated to species status, Spectacled Petrel P. conspicillata, based on differences in morphometrics, vocalisations and breeding phenology. Cytochrome b sequences support species status for the Spectacled Petrel and show that the White-chinned Petrel has two regional populations, one around New Zealand and one throughout the South Atlantic and Indian Oceans. White-chinned and Spectacled Petrels segregated approximately 0.90 million years ago by allopatric fragmentation, and the two populations within White-chinned Petrels diverged approximately 0.35 million years ago. Climate changes and corresponding changes in ocean currents are most likely responsible for these patterns.

Genetic differentiation between Príncipe Island and mainland populations of the grey parrot (Psittacus erithacus), and implications for conservation.

The range of the grey parrot (Psittacus erithacus), one of the most heavily harvested bird species for the international pet trade, spans the forest belt of Central and West Africa and includes the oceanic island of Príncipe (Gulf of Guinea). Morphological variation led to the recognition of two mainland subspecies (P. e. erithacus and P. e. timneh). The population from Príncipe was originally described as a separate species (P. princeps) but is currently included in the nominate race. We used 1932 bp of the mitochondrial genome to clarify the genealogical affinities between the two currently-recognized mainland subspecies and the Príncipe population. Sampling included 20 individuals from Príncipe, 17 from P. e. erithacus, and 13 from P. e. timneh. We found that the two mainland subspecies form two independent lineages, having diverged up to 2.4 million years ago (Ma), and that the Príncipe population is composed of two lineages that diverged in allopatry. The most common lineage is descended from the first colonizers and evolved in isolation for up to 1.4 Ma. Contrary to current understanding, this 'Príncipe lineage' is more closely related to the timneh than to the erithacus subspecies. The second lineage consists of P. e. erithacus birds from the nearby mainland that colonized the island in recent times. The evolutionary dynamics of the grey parrot population of Príncipe are primarily characterized by isolation, with new genetic variation being added through rare immigration events. The heavily harvested Príncipe grey parrot population should therefore be treated as an independent conservation unit.

Social common mole-rats enhance outbreeding via extra-pair mating.

Females in many species engage in matings with males that are not their social mates. These matings are predicted to increase offspring heterozygosity and fitness, and thereby prevent the deleterious effects of inbreeding. We tested this hypothesis in a cooperative breeding mammal, the common mole-rat Cryptomys hottentotus hottentotus. Laboratory-based studies suggested a system of strict social monogamy, while recent molecular studies indicate extensive extra-pair paternity despite colonies being founded by an outbred pair. Our data show that extra-pair and within-colony breeding males differed significantly in relatedness to breeding females, suggesting that females may gain genetic benefits from breeding with non-resident males. Extra-colony male mating success was not based on heterozygosity criteria at microsatellite loci; however, litters sired by extra-colony males exhibited increased heterozygosity. While we do not have the data that refute a relationship between individual levels of inbreeding (Hs) and fitness, we propose that a combination of both male and female factors most likely explain the adaptive significance of extra-pair mating whereby common mole-rats maximize offspring fitness by detecting genetic compatibility with extra-pair mates at other key loci, but it is not known which sex controls these matings.

Genetic variation and population structure in remnant populations of black rhinoceros, Diceros bicornis, in Africa.

Black rhinoceros (Diceros bicornis) are one of the most endangered mammal species in Africa, with a population decline of more than 96% by the end of the last century. Habitat destruction and encroachment has resulted in fragmentation of the remaining populations. To assist in conservation management, baseline information is provided here on relative genetic diversity and population differentiation among the four remaining recognized subspecies. Using microsatellite data from nine loci and 121 black rhinoceros individuals, and comparing the results with those of other African species affected in similar ways, Diceros bicornis michaeli retained the most genetic diversity (heterozygosity 0.675) compared with Diceros bicornis minor (0.459) and Diceros bicornis bicornis (0.505), suggesting that the duration of the known bottlenecks in these populations has only had a limited impact on diversity. Comparable and moderate degrees of population differentiation were found between D. b. minor, D. b. bicornis and D. b. michaeli. Results from the single sample available of the most endangered subspecies, Diceros bicornis longipes, showed the least diversity of all individuals examined. This information should assist conservation management decisions, especially those affecting population viability assessments and selection of individuals for translocations, and will also facilitate subspecies identification for ex situ individuals of uncertain origin.