PUBLICATION

A highly conserved zebrafish IMPDH retinal isoform produces the majority of guanine and forms dynamic protein filaments in photoreceptor cells

Authors

Cleghorn, W.M., Burrell, A.L., Giarmarco, M.M., Brock, D.C., Wang, Y., Chambers, Z.S., Du, J., Kollman, J.M., Brockerhoff, S.E.

ID

ZDB-PUB-211129-6

Date

2021

Source

The Journal of biological chemistry 298(1): 101441 (Journal)

Registered Authors

Brockerhoff, Susan

Keywords

none

MeSH Terms

Retinal Cone Photoreceptor Cells*/cytology
Retinal Cone Photoreceptor Cells*/enzymology
Retinal Cone Photoreceptor Cells*/metabolism
Animals
Zebrafish
IMP Dehydrogenase*/metabolism
Retina/cytology
Retina/metabolism
Isoenzymes/metabolism
Guanine*/metabolism

(all 10)

PubMed

34813793 Full text @ J. Biol. Chem.

Abstract

Inosine monophosphate dehydrogenase (IMPDH) is a key regulatory enzyme in the de novo synthesis of the purine base guanine. Dominant mutations in human IMPDH1 cause photoreceptor degeneration for reasons that are unknown. Here we sought to provide some foundational information on Impdh1a in the zebrafish retina. We found that in zebrafish, gene sub-functionalization due to ancestral duplication resulted in a predominant retinal variant expressed exclusively in rod and cone photoreceptors. This variant is structurally and functionally similar to the human IMPDH1 retinal variant and shares a reduced sensitivity to GTP-mediated inhibition. We also demonstrated that Impdh1a forms prominent protein filaments in vitro and in vivo in both rod and cone photoreceptor cell bodies, synapses, and to a lesser degree, in outer segments. These filaments changed length and cellular distribution throughout the day consistent with diurnal changes in both mRNA and protein levels. Loss of Impdh1a resulted in a substantial reduction of guanine levels, although cellular morphology and cGMP levels remained normal. Our findings demonstrate a significant role for IMPDH1 in photoreceptor guanine production and provide fundamental new information on the details of this protein in the zebrafish retina.

Genes / Markers

Figures

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Expression

Gene	Fish	Conditions	Stage	Anatomy	Assay	Figure
gatd3l	AB	standard conditions	Adult	retina	RTPCR	Fig. 3
gatd3l	AB	standard conditions	Adult	retinal cone cell	RTPCR	Fig. 5
gatd3l	AB	standard conditions	Adult	retinal rod cell	RTPCR	Fig. 5
gatd3l	impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retinal cone cell	RTPCR	Fig. 5
gatd3l	impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retinal rod cell	RTPCR	Fig. 5
gatd3l	rho^fl9 (AB)	standard conditions	Adult	retina	RTPCR	Fig. 3
gatd3l	w248Tg (AB)	standard conditions	Adult	retina	RTPCR	Fig. 3
gnat1	AB	standard conditions	Adult	retina	RTPCR	Fig. 3
gnat1	AB	standard conditions	Adult	retinal cone cell	RTPCR	Fig. 5
gnat1	AB	standard conditions	Adult	retinal rod cell	RTPCR	Fig. 5

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Phenotype

Fish	Conditions	Stage	Phenotype	Figure
AB	fasting	Adult	retina mitochondrial chromosome normal amount, normal	Fig. 5
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina impdh1a expression absent, abnormal	Fig. 5
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina impdh1a expression absent, abnormal	Fig. 3
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina impdh1a expression absent, abnormal	Fig. 1
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina impdh1a expression absent, abnormal	Fig. 1
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina impdh1a expression increased amount, abnormal	Fig. 5
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina adenosine 5'-monophosphate normal amount, normal	Fig. 5
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina guanosine 5'-monophosphate decreased amount, abnormal	Fig. 5
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina IMP normal amount, normal	Fig. 5
impdh1a^{sa23234/sa23234} (AB)	standard conditions	Adult	retina mitochondrial chromosome normal amount, normal	Fig. 5

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Mutations / Transgenics

Allele	Construct	Type	Affected Genomic Region
a9		Complex	mpv17
fl9		Small Deletion	rho
sa23234		Point Mutation	impdh1a
ucd1Tg	Tg(-3.2gnat2:EGFP)	Transgenic Insertion
w248Tg	Tg(gnat2:mcu-2A-RFP)	Transgenic Insertion

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Human Disease / Model

Human Disease	Fish	Conditions	Evidence
retinal degeneration			TAS

Sequence Targeting Reagents

Fish

Fish
AB
impdh1a^{sa23234/sa23234} (AB)
impdh1a^{sa23234/sa23234}; ucd1Tg (AB)
impdh1a^sa23234/+ (AB)
rho^fl9 (AB)
ucd1Tg (AB)
w248Tg (AB)

Antibodies

Name	Type	Antigen Genes	Isotypes	Host Organism
Ab1-impdh1a	polyclonal	impdh1a		Rabbit
Ab1-mt-co1	monoclonal		IgG2a	Mouse
Ab2-impdh1a	polyclonal	impdh1a		Rabbit
Ab-4C12	monoclonal			Mouse
Ab16-GFP	polyclonal	GFP	IgY	Chicken

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Orthology

Engineered Foreign Genes

Marker	Marker Type	Name
EGFP	EFG	EGFP
RFP	EFG	RFP

Mapping

Cleghorn et al., 2021 ZDB-PUB-211129-6 PMID:34813793

A highly conserved zebrafish IMPDH retinal isoform produces the majority of guanine and forms dynamic protein filaments in photoreceptor cells

Cleghorn et al., 2021

ZDB-PUB-211129-6
PMID:34813793