PAX6-positive microglia evolve locally in hiPSC-derived ocular organoids.

Microglia are the resident immune cells of the central nervous system (CNS). They govern the immunogenicity of the retina, which is considered to be part of the CNS; however, it is not known how microglia develop in the eye. Here, we studied human-induced pluripotent stem cells (hiPSCs) that had been expanded into a self-formed ectodermal autonomous multi-zone (SEAM) of cells that partially mimics human eye development. Our results indicated that microglia-like cells, which have characteristics of yolk-sac-like linage cells, naturally develop in 2D eye-like SEAM organoids, which lack any vascular components. These cells are unique in that they are paired box protein 6 (PAX6)-positive, yet they possess some characteristics of mesoderm. Collectively, the data support the notion of the existence of an isolated, locally developing immune system in the eye, which is independent of the body's vasculature and general immune system.

A hypomorphic variant in EYS detected by genome-wide association study contributes toward retinitis pigmentosa.

The genetic basis of Japanese autosomal recessive retinitis pigmentosa (ARRP) remains largely unknown. Herein, we applied a 2-step genome-wide association study (GWAS) in 640 Japanese patients. Meta-GWAS identified three independent peaks at P < 5.0 × 10-8, all within the major ARRP gene EYS. Two of the three were each in linkage disequilibrium with a different low frequency variant (allele frequency < 0.05); a known founder Mendelian mutation (c.4957dupA, p.S1653Kfs*2) and a non-synonymous variant (c.2528 G > A, p.G843E) of unknown significance. mRNA harboring c.2528 G > A failed to restore rhodopsin mislocalization induced by morpholino-mediated knockdown of eys in zebrafish, consistent with the variant being pathogenic. c.2528 G > A solved an additional 7.0% of Japanese ARRP cases. The third peak was in linkage disequilibrium with a common non-synonymous variant (c.7666 A > T, p.S2556C), possibly representing an unreported disease-susceptibility signal. GWAS successfully unraveled genetic causes of a rare monogenic disorder and identified a high frequency variant potentially linked to development of local genome therapeutics.

A novel mutation in gelatinous drop-like corneal dystrophy and functional analysis.

We identified a novel mutation of the tumor-associated calcium signal transducer 2 (TACSTD2) gene in a Japanese patient with gelatinous drop-like corneal dystrophy (GDLD). Genetic analysis revealed a novel homozygous mutation (c.798delG, which may result in frameshift mutation p.Lys267SerfsTer4) in the TACSTD2 gene. This mutated gene was devoid of its original function in helping the claudin (CLDN) 1 and 7 proteins transfer from the cytoplasm to the plasma membrane.

Shugoshin forms a specialized chromatin domain at subtelomeres that regulates transcription and replication timing.

A chromosome is composed of structurally and functionally distinct domains. However, the molecular mechanisms underlying the formation of chromatin structure and the function of subtelomeres, the telomere-adjacent regions, remain obscure. Here we report the roles of the conserved centromeric protein Shugoshin 2 (Sgo2) in defining chromatin structure and functions of the subtelomeres in the fission yeast Schizosaccharomyces pombe. We show that Sgo2 localizes at the subtelomeres preferentially during G2 phase and is essential for the formation of a highly condensed subtelomeric chromatin body 'knob'. Furthermore, the absence of Sgo2 leads to the derepression of the subtelomeric genes and premature DNA replication at the subtelomeric late origins. Thus, the subtelomeric specialized chromatin domain organized by Sgo2 represses both transcription and replication to ensure proper gene expression and replication timing.

A conserved non-reproductive GnRH system in chordates.

Gonadotropin-releasing hormone (GnRH) is a neuroendocrine peptide that plays a central role in the vertebrate hypothalamo-pituitary axis. The roles of GnRH in the control of vertebrate reproductive functions have been established, while its non-reproductive function has been suggested but less well understood. Here we show that the tunicate Ciona intestinalis has in its non-reproductive larval stage a prominent GnRH system spanning the entire length of the nervous system. Tunicate GnRH receptors are phylogenetically closest to vertebrate GnRH receptors, yet functional analysis of the receptors revealed that these simple chordates have evolved a unique GnRH system with multiple ligands and receptor heterodimerization enabling complex regulation. One of the gnrh genes is conspicuously expressed in the motor ganglion and nerve cord, which are homologous structures to the hindbrain and spinal cord of vertebrates. Correspondingly, GnRH receptor genes were found to be expressed in the tail muscle and notochord of embryos, both of which are phylotypic axial structures along the nerve cord. Our findings suggest a novel non-reproductive role of GnRH in tunicates. Furthermore, we present evidence that GnRH-producing cells are present in the hindbrain and spinal cord of the medaka, Oryzias latipes, thereby suggesting the deep evolutionary origin of a non-reproductive GnRH system in chordates.