Functional genomics of HMGN3a and SMARCAL1 in early mammalian embryogenesis

Abdullah Kaya,Valentin A Ilyin,Hongfeng Wang,Erdogan Memili,Nelida Rodriguez-Osorio,John J Parrish,Alper Uzun

doi:10.1186/1471-2164-10-183

Abstract

BackgroundEmbryonic genome activation (EGA) is a critical event for the preimplantation embryo, which is manifested by changes in chromatin structure, transcriptional machinery, expression of embryonic genes, and degradation of maternal transcripts. The objectives of this study were to determine transcript abundance of HMGN3a and SMARCAL1 in mature bovine oocytes and early bovine embryos, to perform comparative functional genomics analysis of these genes across mammals.ResultsNew annotations of both HMGN3a and SMARCAL1 were submitted to the Bovine Genome Annotation Submission Database at BovineGenome.org. Careful analysis of the bovine SMARCAL1 consensus gene set for this protein (GLEAN_20241) showed that the NCBI protein contains sequencing errors, and that the actual bovine protein has a high degree of homology to the human protein. Our results showed that there was a high degree of structural conservation of HMGN3a and SMARCAL1 in the mammalian species studied. HMGN3a transcripts were present at similar levels in bovine matured oocytes and 2–4-cell embryos but at higher levels in 8–16-cell embryos, morulae and blastocysts. On the other hand, transcript levels of SMARCAL1 decreased throughout preimplantation development.ConclusionThe high levels of structural conservation of these proteins highlight the importance of chromatin remodeling in the regulation of gene expression, particularly during early mammalian embryonic development. The greater similarities of human and bovine HMGN3a and SMARCAL1 proteins may suggest the cow as a valuable model to study chromatin remodeling at the onset of mammalian development. Understanding the roles of chromatin remodeling proteins during embryonic development emphasizes the importance of epigenetics and could shed light on the underlying mechanisms of early mammalian development.

Highlights

Embryonic genome activation (EGA) is a critical event for the preimplantation embryo, which is manifested by changes in chromatin structure, transcriptional machinery, expression of embryonic genes, and degradation of maternal transcripts
HMGN3a and SMARCAL1 transcripts are highly expressed in bovine oocytes and early embryos The mRNA isolated from oocytes and early embryos exhibited typical ribosomal RNA band ratio (28S:18S)
SMARCAL1 transcripts decrease significantly in the morula and blastocyst stages (Figure 1B). This result differs from our previous microarray and Real-Time PCR gene expression analysis, which showed that SMARCAL1 was expressed at significantly higher levels in 8-cell embryos compared to bovine oocytes [3]

Summary

Introduction

Embryonic genome activation (EGA) is a critical event for the preimplantation embryo, which is manifested by changes in chromatin structure, transcriptional machinery, expression of embryonic genes, and degradation of maternal transcripts. Embryonic development is initiated when mature oocytes (MII) are fertilized by spermatozoa. Maternal factors, such as mRNAs, microRNAs and proteins stored in the oocyte, provide the means of support for the first few days of development. The transition from a maternal to a zygotic control of development, called maternal to zygotic transition (MZT), and the activation of the embryonic genome involve chromatin structural modifications that take place during the first few embryonic cell cycles [1]. Embryonic genome activation (EGA) sets the stage for later development [2,3]. The regulation of chromatin remodeling during EGA still remains a mystery

Objectives

Methods

Results

Conclusion