Summary
The zebrafish is a model organism for studying vertebrate development and many human
diseases. Orthologues of the majority of human coagulation factors are present in
zebrafish, including fibrinogen. As a first step towards using zebrafish to model
human fibrinogen disorders, we cloned the zebrafish fibrinogen cDNAs and made in situ
hybridisations and quantitative reverse transcription-polymerase chain reactions (qRT-PCR)
to detect zebrafish fibrinogen mRNAs. Prior to liver development or blood flow we
detected zebrafish fibrinogen expression in the embryonic yolk syncytial layer and
then in the early cells of the developing liver. While human fibrinogen is encoded
by a three-gene, 50 kilobase (kb) cluster on chromosome 4 (FGB-FGA-FGG), recent genome assemblies showed that the zebrafish fgg gene appears distanced from fga and fgb, which we confirmed by in situ hybridisation. The zebrafish fibrinogen Bβ and γ protein
chains are conserved at over 50% of amino acid positions, compared to the human polypeptides.
The zebrafish Aα chain is less conserved and its C-terminal region is nearly 200 amino
acids shorter than human Aα. We generated transgenic zebrafish which express a green
fluorescent protein reporter gene under the control of a 1.6 kb regulatory region
from zebrafish fgg. Transgenic embryos showed strong fluorescence in the developing liver, mimicking
endogenous fibrinogen expression. This regulatory sequence can now be used for overexpression
of transgenes in zebrafish hepatocytes. Our study is a proof-of-concept step towards
using zebrafish to model human disease linked to fibrinogen gene mutations.
Keywords
Fibrinogen - zebrafish - gene cluster - transgenic - liver