Purchase this article with an account.
Jing Luo, Laura Kakuk-Atkins, Peter Hitchcock; Midkine-a Functions As An Autocrine Regulator Of The Cell Cycle In Retinal Progenitors. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6003.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Midkine is a secreted heparin binding growth factor that has numerous biological functions, both during development and following tissue injury. In the vertebrate retina, midkine is expressed in retinal stem and progenitor cells (Calinescu et al., 2010; Livesey et al., 2004). There are two midkine orthologs in zebrafish, Midkine-a (Mdka) and Midkine-b. The purpose of this study was to use both loss- and gain-of function approaches in zebrafish to investigate the function of Mdka during early retinal development.
Morpholino oligonucletides were injected into embryos to knock down Mdkasynthesis. The Tol2 transposon system was used to generate transgenic lines for conditional gain-of-function. Dividing cells were labeled with either BrdU or EdU. Analysis of Percent Labeled Mitoses, using EdU to label cells in S-phase and antibodies to label cells in M-phase, was used to measure the time for cells to transit from S- to M-phase (G2) of the cell cycle. Standard methods of immunocytochemistry and in situ hybridization were used to identify labeled cells. Western blot analysis from whole embryo lysates was used to evaluate the loss of Mdka and the induction of a Mdka:EGFP fusion protein. Retinas from experimental and control animals were evaluated between 26 and 72 hours post fertilization (hpf).
The loss of Mdka does not alter gross embryonic or larval development, but does result in a transient delay in neuronal differentiation. Labeling with BrdU shows that at 48hpf there is a paucity of differentiated neurons and all cells are proliferative, though there are significantly fewer cells in M-phase. This delay in neuronal differentiation does not result from a delay in initiating molecular developmental events, but results from a lengthening of the cell cycle. The cell cycle is significantly longer in morphants than in wild-type retinas. In contrast to Mdka loss-of-function, the cell cycle is significantly shorter following Mdka gain-of-function.
In retinal stem and progenitor cells, Mdka functions as an autocrine regulator of the cell cycle. This study provides evidence for a novel signaling pathway during early retinal development.
This PDF is available to Subscribers Only