Microfibril-associated glycoprotein 4 (Mfap4) regulates haematopoiesis in zebrafish

Sheena L M Ong,M Meroshini,Yogavalli Poobalan,N Ray Dunn,Ivo J H M De Vos

doi:10.1038/s41598-020-68792-8

Abstract

Microfibril-associated glycoprotein 4 (MFAP4) is an extracellular matrix protein belonging to the fibrinogen-related protein superfamily. MFAP4 is produced by vascular smooth muscle cells and is highly enriched in the blood vessels of the heart and lung, where it is thought to contribute to the structure and function of elastic fibers. Genetic studies in humans have implicated MFAP4 in the pathogenesis of Smith-Magenis syndrome, in which patients present with multiple congenital abnormalities and mental retardation, as well as in the severe cardiac malformation left-sided congenital heart disease. Comprehensive genetic analysis of the role of MFAP4 orthologues in model organisms during development and tissue homeostasis is however lacking. Here, we demonstrate that zebrafish mfap4 transcripts are detected embryonically, resolving to the macrophage lineage by 24 h post fertilization. mfap4 null mutant zebrafish are unexpectedly viable and fertile, without ostensible phenotypes. However, tail fin amputation assays reveal that mfap4 mutants have reduced numbers of macrophages, with a concomitant increase in neutrophilic granulocytes, although recruitment of both cell types to the site of injury was unaffected. Molecular analyses suggest that loss of Mfap4 alters the balance between myeloid and lymphoid lineages during both primitive and definitive haematopoiesis, which could significantly impact the downstream function of the immune system.

Highlights

Microfibril-associated glycoprotein 4 (MFAP4) is an extracellular matrix protein belonging to the fibrinogen-related protein superfamily
As the number of early erythroid cells, polychromatophils, is not altered significantly in adult mfap4∆/∆ mutants (Supplementary Fig. S4), the effect of mfap[4] loss on erythropoiesis remains unclear. Apart from their crucial role in the innate immune response, macrophages and neutrophilic granulocytes are involved in wound healing and tissue regeneration[28,45]
We show that in zebrafish loss of mfap[4], which is conspicuously expressed in macrophages, results in an average of 1.5 times reduction of the total number of macrophages (Fig. 3) and a concomitant increase in the number of neutrophils (Fig. 4)

Summary

Introduction

Microfibril-associated glycoprotein 4 (MFAP4) is an extracellular matrix protein belonging to the fibrinogen-related protein superfamily. MFAP4 is produced by vascular smooth muscle cells and is highly enriched in the blood vessels of the heart and lung, where it is thought to contribute to the structure and function of elastic fibers. We subsequently demonstrated by chromatin immunoprecipitation coupled with massively parallel deep sequencing (ChIP-Seq) that MFAP4 is directly bound by the Activin/Nodal effector proteins SMAD2/3, as well as the T-box transcription factor EOMESODERMIN (EOMES) in differentiating hESCs16,17. These findings strongly suggest that MFAP4 is a direct target of SMAD2/3/EOMES transcriptional regulation during the earliest events of germ layer specification in the developing mammalian embryo. Coupling our larval and adult mfap[4] loss-of-function zebrafish with tail fin injury models, we investigated the role of Mfap[4] in the zebrafish innate immune system and revealed an unexpected role for Mfap[4] in regulating lineage restriction during haematopoiesis

Methods

Findings

Conclusion