Ptf1a is expressed transiently in all types of amacrine cells in the embryonic zebrafish retina

Patricia R Jusuf,William A Harris

doi:10.1186/1749-8104-4-34

Abstract

BackgroundThe vertebrate retina is composed of five major types of neurons: three excitatory (photoreceptors, bipolar cells and ganglion cells) and two inhibitory (horizontal and amacrine cells). The transcription factor Ptf1a (pancreas transcription factor 1a) is important for the normal development of the inhibitory retinal neurons.ResultsUsing a transgenic Ptf1a:GFP reporter and in situ hybridization in the zebrafish retina, we show that ptf1a message is transiently expressed in all amacrine and horizontal cells within hours after the terminal division of multipotent progenitors at the apical surface of the retinal neuroepithelium, and remains on as these cells migrate to their final laminar location. The message then shuts off, but we can follow the stable Ptf1a:GFP protein for up to 120 hours post-fertilization. A variety of anatomically and neurochemically distinct subtypes of amacrine cells can already be distinguished at this embryonic time point.ConclusionThe timing of Ptf1a expression suggests that it is involved in the very early stages or steps in the differentiation of amacrine cells, which, due to the perdurance of the Ptf1a:GFP, can be seen to rapidly diversify into a large number of subtypes. This work sets the stage for future studies looking at genetic specification of amacrine subtypes.

Highlights

The vertebrate retina is composed of five major types of neurons: three excitatory and two inhibitory
To ensure that the retinal cells that express pancreas transcription factor 1a (Ptf1a):green fluorescent protein (GFP) reflect the expression of endogenous ptf1a gene, the spatio-temporal expression pattern of ptf1a RNA was studied using in situ hybridization and compared to the expression of GFP in the transgenic line
Expression in wholemount transgenic zebrafish heads is shown at different ages. (A) Endogenous ptf1a RNA expression was revealed by in situ hybridization visualized by BM purple. (B) GFP reporter protein expression of Tg(ptf1a:GFP) embryos

Summary

Introduction

The vertebrate retina is composed of five major types of neurons: three excitatory (photoreceptors, bipolar cells and ganglion cells) and two inhibitory (horizontal and amacrine cells). Ptf1a is important for the generation of many inhibitory (primarily γ-aminobutyric acid (GABA)-ergic) interneurons in different areas, such as the spinal cord [811] and cerebellum [7,12], in specific other central nervous system regions it is involved in the specification of excitatory glutamatergic neurons [13]. Ptf1a is expressed in the horizontal and amacrine cell populations. Studies in Xenopus and mouse retina show that Ptf1a is both essential and sufficient for determining the fates of these inhibitory neuronal types (page number not for citation purposes)

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