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theses

Retinal development involves defined guidance of neuronal axons to their destined cells through cell adhesion molecules, by compilation of cell-cell connections at synapses. Cell adhesion molecules promote oriented axonal outgrowth and help in target synaptic specificity to maintain histoarchitecture of retina. Cell adhesion molecules like cadherins are the products of expression of long genes >200 kilobases of genomic DNA. Topoisomerase II beta (Top2b) involved in modulating DNA supercoiling by catalyzing the double strand breaks and passing the stands through one another. Top2b is pervasively expressed in all terminally differentiated cells and participates in gene transcription. Recent studies have shown that Top2b facilitates the expression of long genes. However, its particular role in transcription of cadherins and effect on organization of retinal cells such as retinal ganglion cells and horizontal cells remain unclear. In current study, the role of Top2b in expression of cadherin genes was analyzed in iii developing chick retina via immunohistochemistry and real-time PCR. Top2b function in developing retina was inhibited by injections of 500µM Top2b catalytic inhibitor (ICRF-193) into sub-retinal space at embryonic day 4 (E4). Retinal tissues were analyzed by immunohistochemistry using cell specific markers, e.g., Brn3a for ganglion cells, 4F2 for horizontal cells, and Tuj1 for neuronal processes at E6, E8, E10, and E12. We showed that inhibition of Top2b by ICRF-193 i) reduced the expression level of cadherin genes, e.g., N-cadherin (Cdh2), Cadherin-6B (Cad6B), Cadherin-7 (Cdh7), and Cadhrin-8 (Cdh8)in developing retina; ii)led to a disoriented cellular organization; and iii) delayed migration of RGCs and HCs. The results from immunohistochemistry were confirmed by quantitative real-time PCR (qRT-PCR). Results from qRT-PCR showed significant reduction in expression levels of cadherin genes, e.g., Cad6B and Cdh7 with an average fold reduction of 2.5 prominent at embryonic day 10 (E10) (p <0.02, p<0.006), respectively and Cdh8 with an average fold reduction of 4 prominent at embryonic day 8 (E8) (p <0.02), however expression of Cdh2 was not effected by Top2b inhibition at E6-E12. This study helps to understand the molecular basis of vertebrate retinal development via calcium-dependent intercellular cell adhesion molecules and revealed the vital role of Top2b in expression of cadherin genes.

ETD_7607

M.S.

Includes bibliographical references

by Rameshwari Rayaji

doi:10.7282/T35M682B

ETD graduate

The author owns the copyright to this work.