![]() However, this relationship has not been directly demonstrated. Defects in melanin biogenesis in albinism have thus been thought to influence the pace of cell production, and consequently the specification of ipsilateral RGCs. The timing of melanin formation in pigmented mice coincides with the onset of RGC production. The underlying mechanisms that cause the reduction of Zic2-expressing cells, however, are poorly understood. ![]() In albino mice, fewer RGCs express Zic2 during embryonic development, reflecting the reduction of the ipsilateral projection. The transcription factor Islet2 is expressed in contralateral RGCs (approximately 30% throughout the retina), but regulates only the late born crossed RGC projection from VT retina. ![]() The zinc-finger transcription factor Zic2 is expressed transiently in VT RGCs that project ipsilaterally between E14.5 and E17.5 and is critical for the formation of this projection. The pathway choice of an RGC axon at the optic chiasm is dependent on transcription factors that direct the expression of guidance receptors. In addition, a population of RGCs in the VT retina that are born during late embryogenesis (approximately E15.5 to P0) projects contralaterally. Ipsilateral RGCs are produced during a shorter time span, approximately E11.5 to E16.5, and specifically in the ventrotemporal (VT) region of the retina. In mice, contralateral RGC production begins in the center of the retina at embryonic day (E)11.5 and continuously expands to the periphery until postnatal day (P)0. A hallmark of all albino mammals is a diminished ipsilateral projection. In humans, 40% of RGCs project ipsilaterally, whereas in mice, only 3 to 5% of RGCs project ipsilaterally. This ensures that higher visual centers receive information from both eyes to implement depth perception. Retinal ganglion cells (RGCs) establish the connections for binocular vision by projecting their axons either to the same (ipsilateral) or the opposite (contralateral) side of the brain. These abnormalities include defects in optic development and function, including impaired binocular vision. In the eyes, the perturbation of melanogenesis is specifically in the retinal pigment epithelium (RPE), where it relates to numerous abnormalities of the visual pathways. Albinism is a genetic disorder associated with a disruption of melanin synthesis, resulting in the loss of pigmentation in the eyes, hair and skin or eyes only. ![]()
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