Pigmentary glaucoma (PG) is a common glaucoma subtype that results from release of pigment from the iris, called pigment dispersion syndrome (PDS), and its deposition throughout the anterior chamber of the eye. Although PG has a substantial heritable component, no causative genes have yet been identified. We used whole exome sequencing of two independent pedigrees to identify two premelanosome protein (PMEL) variants associated with heritable PDS/PG. PMEL encodes a key component of the melanosome, the organelle essential for melanin synthesis, storage and transport. Targeted screening of PMEL in three independent cohorts (n = 394) identified seven additional PDS/PG-associated non-synonymous variants. Five of the nine variants exhibited defective processing of the PMEL protein. In addition, analysis of PDS/PG-associated PMEL variants expressed in HeLa cells revealed structural changes to pseudomelanosomes indicating altered amyloid fibril formation in five of the nine variants. Introduction of 11-base pair deletions to the homologous pmela in zebrafish by the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 method caused profound pigmentation defects and enlarged anterior segments in the eye, further supporting PMEL's role in ocular pigmentation and function. Taken together, these data support a model in which missense PMEL variants represent dominant negative mutations that impair the ability of PMEL to form functional amyloid fibrils. While PMEL mutations have previously been shown to cause pigmentation and ocular defects in animals, this research is the first report of mutations in PMEL causing human disease.

We explore the ideas and advances surrounding the genetic basis of pigment dispersion syndrome (PDS) and pigmentary glaucoma (PG). As PG is the leading cause of nontraumatic blindness in young adults and current tailored interventions have proven ineffective, a better understanding of the underlying causes of PDS, PG, and their relationship is essential. Despite PDS being a subclinical disease, a large proportion of patients progress to PG with associated vision loss. Decades of research have supported a genetic component both for PDS and conversion to PG. We review the body of evidence supporting a genetic basis in humans and animal models and reevaluate classical mechanisms of PDS/PG considering this new evidence.

The Neurospora crassa nuclear aod-1 gene encodes an alternative oxidase that functions in mitochondria. The enzyme provides a branch from the standard electron transport chain by transferring electrons directly from ubiquinol to oxygen. In standard laboratory strains, aod-1 is transcribed at very low levels under normal growth conditions. However, if the standard electron transport chain is disrupted, aod-1 mRNA expression is induced and the AOD1 protein is produced. We previously identified a strain of N. crassa, that produces high levels of aod-1 transcript under non-inducing conditions. Here we have crossed this strain to a standard lab strain and determined the genomic sequences of the parents and several progeny. Analysis of the sequence data and the levels of aod-1 mRNA in uninduced cultures revealed that a frameshift mutation in the flbA gene results in the high uninduced expression of aod-1. The flbA gene encodes a regulator of G protein signaling that decreases the activity of the Gα subunit of heterotrimeric G proteins. Our data suggest that strains with a functional flbA gene prevent uninduced expression of aod-1 by inactivating a G protein signaling pathway, and that this pathway is activated in cells grown under conditions that induce aod-1. Induced cells with a deletion of the gene encoding the Gα protein still have a partial increase in aod-1 mRNA levels, suggesting a second pathway for inducing transcription of the gene in N. crassa. We also present evidence that a translational control mechanism prevents production of AOD1 protein in uninduced cultures.

Balancing self-renewal and differentiation is a key feature of every stem cell niche and one that is tuned by mechanical interactions of cells with their neighbors and surrounding extracellular matrix. The fibrous stem cell niches that develop as sutures between skull bones must balance the complex extracellular environment that emerges to define them with self-renewal and bone production. Here, we address the role for physical stimuli in suture development by probing the relationship between nuclear shape, organization and gene expression in response to a developing collagen network in embryonic midline sutures. This work complements genetic approaches used to study sutures and provides the first quantitative analyses of physical structure in these sutures. By combining multiple imaging modalities with novel shape description, in addition to network analysis methods, we find the early emergence of a complex extracellular collagen network to have an important role in regulating morphogenesis and cell fate. We show that disrupted collagen crosslinking can alter ECM organization of midline sutures as well as stimulate expression of bone differentiation markers. Further, our findings suggest that in vivo, skeletal tissues can uncouple the response of the nuclear lamina from collagen mediated tissue stiffening seen in vitro. Our findings highlight a crucial relationship between the cellular microenvironment, tissue stiffness and geometry with gene expression in normal development and maintenance of progenitor fate in embryonic sutures.

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