Chromosome 10q26-driven age-related macular degeneration is associated with reduced levels of HTRA1 in human retinal pigment epithelium.

Genome-wide association studies have identified the chromosome 10q26 (Chr10) locus, which contains the age-related maculopathy susceptibility 2 (ARMS2) and high temperature requirement A serine peptidase 1 (HTRA1) genes, as the strongest genetic risk factor for age-related macular degeneration (AMD) [L.G. Fritsche et al., Annu. Rev. Genomics Hum. Genet. 15, 151-171, (2014)]. To date, it has been difficult to assign causality to any specific single nucleotide polymorphism (SNP), haplotype, or gene within this region because of high linkage disequilibrium among the disease-associated variants [J. Jakobsdottir et al. Am. J. Hum. Genet. 77, 389-407 (2005); A. Rivera et al. Hum. Mol. Genet. 14, 3227-3236 (2005)]. Here, we show that HTRA1 messenger RNA (mRNA) is reduced in retinal pigment epithelium (RPE) but not in neural retina or choroid tissues derived from human donors with homozygous risk at the 10q26 locus. This tissue-specific decrease is mediated by the presence of a noncoding, cis-regulatory element overlapping the ARMS2 intron, which contains a potential Lhx2 transcription factor binding site that is disrupted by risk variant rs36212733. HtrA1 protein increases with age in the RPE-Bruch's membrane (BM) interface in Chr10 nonrisk donors but fails to increase in donors with homozygous risk at the 10q26 locus. We propose that HtrA1, an extracellular chaperone and serine protease, functions to maintain the optimal integrity of the RPE-BM interface during the aging process and that reduced expression of HTRA1 mRNA and protein in Chr10 risk donors impairs this protective function, leading to increased risk of AMD pathogenesis. HtrA1 augmentation, not inhibition, in high-risk patients should be considered as a potential therapy for AMD.

Ultrastructure of the Gregarina niphandrodes nucleus through stages from unassociated trophozoites to gamonts in syzygy and the syzygy junction.

In Gregarina niphandrodes, an apicomplexan parasite, the sexual stage of its life cycle begins with the association of 2 gamonts. Here, we describe the ultrastructure of the syzygy junction and the nucleus during the transition from unassociated trophozoites to paired gamonts to gamonts in syzygy. Throughout this process, the folds within the syzygy junction undergo changes that correspond to changes of the epicytic folds. The nucleus goes through dramatic changes from multiple spheres of condensed chromatin in unassociated trophozoites, to mostly uncondensed chromatin in paired gamonts, to a large single sphere of condensed chromatin encasing many smaller spheres in gamonts in syzygy. These differing nuclear ultrastructures reflect the dramatic cellular and transcriptional changes associated with life cycle transitions and are indicative of the numerous cell divisions that follow.

Gregarina niphandrodes may lack both a plastid genome and organelle.

Gregarines are early diverging apicomplexans that appear to be closely related to Cryptosporidium. Most apicomplexans, including Plasmodium, Toxoplasma, and Eimeria, possess both plastids and corresponding plastid genomes. Cryptosporidium lacks both the organelle and the genome. To investigate the evolutionary history of plastids in the Apicomplexa, we tried to determine whether gregarines possess a plastid and/or its genome. We used PCR and dot-blot hybridization to determine whether the gregarine Gregarina niphandrodes possesses a plastid genome. We used an inhibitor of plastid function for any reduction in gregarine infection, and transmission electron microscopy to search for plastid ultrastructure. Despite an extensive search, an organelle of the appropriate ultrastructure in transmission electron microscopy, was not observed. Triclosan, an inhibitor of the plastid-specific enoyl-acyl carrier reductase enzyme, did not reduce host infection by G. niphandrodes. Plastid-specific primers produced amplicons with the DNA of Babesia equi, Plasmodium falciparum, and Toxoplasma gondii as templates, but not with G. niphandrodes DNA. Plastid-specific DNA probes, which hybridized to Babesia equi, failed to hybridize to G. niphandrodes DNA. This evidence indicates that G. niphandrodes is not likely to possess either a plastid organelle or its genome. This raises the possibility that the plastid was lost in the Apicomplexan following the divergence of gregarines and Cryptosporidium.