Transcriptional profiling of embryos lacking the lipoprotein receptor SR-B1 reveals a regulatory circuit governing a neurodevelopmental or metabolic decision during neural tube closure

Nicolás Santander,Paz Molina,Katherine Rivera,Alberto J M Martin,Carlos Lizama,Leandro Murgas,Alejandro Godoy,Sebastián Contreras,Dolores Busso,Francisca Salas-Pérez,Attilio Rigotti,Alonso Quiroz

doi:10.1186/s12864-018-5110-2

Abstract

BackgroundThe high-density lipoprotein receptor SR-B1 mediates cellular uptake of several lipid species, including cholesterol and vitamin E. During early mouse development, SR-B1 is located in the maternal-fetal interface, where it facilitates vitamin E transport towards the embryo. Consequently, mouse embryos lacking SR-B1 are vitamin E-deficient, and around half of them fail to close the neural tube and show cephalic neural tube defects (NTD). Here, we used transcriptomic profiling to identify the molecular determinants of this phenotypic difference between SR-B1 deficient embryos with normal morphology or with NTD.ResultsWe used RNA-Seq to compare the transcriptomic profile of three groups of embryos retrieved from SR-B1 heterozygous intercrosses: wild-type E9.5 embryos (WT), embryos lacking SR-B1 that are morphologically normal, without NTD (KO-N) and SR-B1 deficient embryos with this defect (KO-NTD). We identified over 1000 differentially expressed genes: down-regulated genes in KO-NTD embryos were enriched for functions associated to neural development, while up-regulated genes in KO-NTD embryos were enriched for functions related to lipid metabolism. Feeding pregnant dams a vitamin E-enriched diet, which prevents NTD in SR-B1 KO embryos, resulted in mRNA levels for those differentially expressed genes that were more similar to KO-N than to KO-NTD embryos. We used gene regulatory network analysis to identify putative transcriptional regulators driving the different embryonic expression profiles, and identified a regulatory circuit controlled by the androgen receptor that may contribute to this dichotomous expression profile in SR-B1 embryos. Supporting this possibility, the expression level of the androgen receptor correlated strongly with the expression of several genes involved in neural development and lipid metabolism.ConclusionsOur analysis shows that normal and defective embryos lacking SR-B1 have divergent expression profiles, explained by a defined set of transcription factors that may explain their divergent phenotype. We propose that distinct expression profiles may be relevant during early development to support embryonic nutrition and neural tube closure.

Highlights

The high-density lipoprotein receptor Scavenger Receptor class B type 1 (SR-B1) mediates cellular uptake of several lipid species, including cholesterol and vitamin E
We analyzed the data using hierarchical clustering and principal component analysis (Fig. 1b-c). These analyses show that the samples within each group tend to cluster together, and that wild-type E9.5 embryos (WT) and knock out (KO)-N groups are closer from each other than to the KO-neural tube defects (NTD) group
WT and KO morphologically normal embryos (KO-N) samples cluster separately and have 129 differentially expressed genes. These initial analyses showed that most of the differentially expressed genes are associated to the neural phenotype, since KO embryos with NTD (KO-NTD) embryos have the most differentially expressed genes compared to WT and KO-N embryos

Summary

Introduction

The high-density lipoprotein receptor SR-B1 mediates cellular uptake of several lipid species, including cholesterol and vitamin E. The Scavenger Receptor class B type 1 (SR-B1) is a multiligand receptor that binds several classes of lipoproteins It acts as the major receptor for high density lipoproteins (HDL) in the adult mouse [1]. SR-B1 binds HDL with high affinity and mediates selective, non-endocytic uptake as well as efflux of lipids by cells [2] This receptor plays a key role in regulating circulating cholesterol levels because it is responsible for the clearance of plasma cholesterol in the liver for its excretion in bile [3]. In steroidogenic cells, such as adrenocortical cells and ovarian granulosa cells, SR-BI mediates the uptake of HDL-cholesteryl esters to be used a substrate for steroid hormone synthesis [4, 5]. SR-B1 mediates the transport of other classes of lipids, including the lipophilic vitamins A, D, and E [6,7,8,9]

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