We investigate mutations in trβ2, a splice variant of thrb, identifying changes in function, structure, and behavior in larval and adult zebrafish retinas. Two N-terminus CRISPR mutants were identified. The first is a 6BP+1 insertion deletion frameshift resulting in a truncated protein. The second is a 3BP in frame deletion with intact binding domains. ERG recordings of isolated cone signals showed that the 6BP+1 mutants did not respond to red wavelengths of light while the 3BP mutants did respond. 6BP+1 mutants lacked optomotor and optokinetic responses to red/black and green/black contrasts. Both larval and adult 6BP +1 mutants exhibit a loss of red-cone contribution to the ERG and an increase in UV-cone contribution. Transgenic reporters show loss of cone trβ2 activation in the 6BP+1 mutant but increase in the density of cones with active blue, green, and UV opsin genes. Antibody reactivity for red-cone LWS1 and LWS2 opsin was absent in the 6BP+1 mutant, as was reactivity for arrestin3a. Our results confirm a critical role for trβ2 in long-wavelength cone development.
We investigate a splice variant of thrb isolated in the retina, trβ2, identifying functional changes in larval and adult mutant zebrafish lacking trβ2. We constructed two CRISPR mutant zebrafish with mutations located in the N-terminus region. The first is a 6BP+1 insertion deletion frameshift resulting in a truncated protein. The second is a 3BP in frame deletion with intact binding domains. ERG recordings showed that the 6BP+1 mutants did not respond to red wavelengths of light while the 3BP mutants did respond. 6BP+1 mutants lacked optomotor and optokinetic responses to red/black and green/black contrasts. Adult 6BP+1 mutants exhibit a loss of red-cone contribution to the ERG, and an increase in green and UV contributions. Anatomical markers show loss of red-cones in the 6BP+1 mutant but increase in blue, green, and UV cone density. Our results confirm trβ2's role in retinal cone development. Author SummaryThere are four cone photoreceptors responsible for color vision in zebrafish: red, green, blue, and UV. The thyroid hormone receptor trβ2 is localized in the vertebrate retina. We know that it is necessary for the development of long-wavelength-sensitive cones (red), but here we investigate the functional alterations that accompany a loss of trβ2. Our work contributes to the ongoing investigations of retinal development and the involvement of thyroid hormone receptors. Confirming previous morphological findings, we see that the fish become red colorblind when trβ2 is knocked out, but the contributions of the other three cone types shift in response. Our work highlights the plasticity of the retinal circuit as we see changes in opsin peaks and cone sensitivity, increases in contributions of UV cones, and an attempt at a mosaic pattern in the adult retina all in the absence of trβ2 and red cones. We now have an increased understanding of mechanisms underlying retinal development ResultsCRISPR mutations are located in the N-terminus of trβ2. The two splice variants of the thrb gene, trβ1 and trβ2 differ only in the first exon [14]. To target trβ2, we designed gRNA targeting exon1 of trβ2 and injected into one-cell-stage eggs of tg(trβ2:tdTomato). We isolated
BACKGROUND Superficial siderosis is the deposition of hemosiderin in the superficial layers of the central nervous system. It has been described in patients with chronic leakage of blood into the cerebrospinal fluid or with amyloid angiopathy, often associated with Alzheimer’s disease (AD). OBSERVATIONS We present two cases of superficial siderosis with vastly different symptomatologies and treatment courses. The patient in case 1 had diffuse superficial siderosis demonstrated on T2-weighted magnetic resonance imaging (MRI), appearing mostly in the inferior cerebellum and extending throughout the neuraxis. He presented with hearing loss, spasticity, gait abnormalities, and urinary incontinence. Ultimately, surgical exploration of the thoracic spinal dura revealed an arteriovenous fistula, which was obliterated. His clinical course stabilized but with persistent deficits. The patient in case 2 had a family history of AD and underwent MRI to evaluate for memory impairment, which demonstrated superficial siderosis of the left occipital lobe. Lumbar puncture demonstrated only traumatic contamination by red blood cells, but tau protein analysis was consistent with the diagnosis of AD. LESSONS Superficial siderosis is a diagnostic term prompted by findings on MRI that can arise due to two different pathological entities. The diagnosis in case 1 should be termed diffuse superficial siderosis and in case 2 should be termed lobar cortical siderosis.
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