A gene regulatory network of vertebrate retina development

  • Author / Creator
    Hejazi, Maryam
  • Gene regulatory networks (GRN) play a central role in the specification, differentiation and function of the central nervous system (CNS) during development. During vertebrate retinal development, six types of neural cells and one type of glial cell are specified in a temporal order from a pool of multipotent retinal progenitor cells (RPC). There has been extensive research on the competence model of retinal development. An attractive hypothesis explains that RPCs follow through a series of competent states, which are intrinsically regulated, and thus cell fate choices are intrinsically defined. There are transcriptional and translational differences between progenitor cells at different stages of development, which make RPC populations heterogeneous at different time points of development. Transcription factors (TFs) are one of the intrinsic factors that drive the RPC towards various cell fates. TFs regulate each other in a transcriptional regulatory network to alter RPC competency and drive them towards becoming various specialized cell types (Cepko et al., 2014).
    We were interested in GRN of the distal-less homedomain TF DLX family in the development of the vertebrate retina. Dlx1/Dlx2 double knock out (DKO) mice die at birth with multiple congenital anomalies (Anderson, Qiu, et al., 1997). We have assessed the retinal phenotype in the Dlx1/Dlx2 DKO mice. At post-natal day 0 (P0), there is a reduced amount of retinal ganglion cells (RGCs) (33%) and decreased Brn3a and Brn3b (RGC markers) expression in the ganglion cell layer (GCL) (de Melo et al., 2005). Of significance, there is increased and ectopic expression of Crx, supporting an alternative cell fate in the Dlx1/Dlx2 null retina (de Melo et al., 2005). In addition, Dlx2 expression is highest in early differentiation (embryonic day 13/E13) and later during adulthood (de Melo et al., 2003). This might explain the involvement of Dlx2 in early RPC fate specification and later for RGC maintenance. Based on my results, I suggested a possible GRN of Dlx2/Crx/miR-124 in the determination of RGC cell fate with concomitant repression of photoreceptor (PR) differentiation at E18. I also suggested, that Dlx2 may have a temporal function working with Otx2 in retinal progenitor cells (RPC) at E13.
    Unlike the mouse, there have not been any studies on the expression and function of dlx genes in the zebrafish eye during development or in adulthood. Based on our lab’s preliminary data, we did not find dlx gene family expression in the zebrafish eye, limiting further study of their role in zebrafish eye development. During evolution of the zebrafish, dlx gene orthologue expression appears to be lost in the zebrafish retina, but their expression and function is conserved in the forebrain and pharyngeal arches. However, the absence or the low levels of endogenous expression of dlx genes might assist us in studying its function by expressing one of the mice Dlx genes in the zebrafish eye during embryogenesis. Thus, I investigated the role of Dlx genes in the eye during evolution by expressing mouse Dlx2 in the zebrafish eye. I generated mouse Dlx2 transgenic retina Tg[rx3:Dlx2] of zebrafish to further investigate Dlx gene expression and function in the retina during vertebrate evolution.
    Retinal vasculature development is also critical for ocular development, and its developmental process is tightly connected with retinal neuronal development (Paredes et al., 2018). Neuropilin family member are critical for vascular, cardiovascular, and neuronal development (Kawasaki et al., 1999). While there have been a few reports regarding Nrp1’s role during retinal vasculature development, very little is known about the role of Nrp2 during eye development (Pellet-Many et al., 2008). Nrp2 expression was observed in the choroid and hyaloid vessels starting at early retinal development, and in the RGC during later developmental stages. We demonstrated Nrp2’s critical role in retinal neurovascular development, as retina structure and physiology of adult mice was disrupted in Nrp2 KO mice. We also demonstrated the possible connection between neuronal and vasculature development, as retinal neuronal cell expression was changed in Nrp2 KO mice. Collectively, my research has contributed to a better understanding of some of the mechanisms underlying vertebrate retinal development.

  • Subjects / Keywords
  • Graduation date
    Fall 2019
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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