Maternal Transcripts of Hox Genes Are Found in Oocytes of Platynereis dumerilii (Annelida, Nereididae).

Georgy P Maslakov,Alina A Surkova,Nikita S Kulishkin,Milana A Kulakova

doi:10.3390/jdb9030037

Georgy P Maslakov, Alina A Surkova + Show 2 more

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https://doi.org/10.3390/jdb9030037

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Abstract

Hox genes are some of the best studied developmental control genes. In the overwhelming majority of bilateral animals, these genes are sequentially activated along the main body axis during the establishment of the ground plane, i.e., at the moment of gastrulation. Their activation is necessary for the correct differentiation of cell lines, but at the same time it reduces the level of stemness. That is why the chromatin of Hox loci in the pre-gastrulating embryo is in a bivalent state. It carries both repressive and permissive epigenetic markers at H3 histone residues, leading to transcriptional repression. There is a paradox that maternal RNAs, and in some cases the proteins of the Hox genes, are present in oocytes and preimplantation embryos in mammals. Their functions should be different from the zygotic ones and have not been studied to date. Our object is the errant annelid Platynereis dumerilii. This model is convenient for studying new functions and mechanisms of regulation of Hox genes, because it is incomparably simpler than laboratory vertebrates. Using a standard RT-PCR on cDNA template which was obtained by reverse transcription using random primers, we found that maternal transcripts of almost all Hox genes are present in unfertilized oocytes of worm. We assessed the localization of these transcripts using WMISH.

Highlights

Genome-wide studies that investigate developmental processes have shown thatMetazoan genomes are pervasively transcribed in oogenesis to create the complexity necessary for early development, that is, during the period when the zygotic genome is not yet working
We tested primers for Platynereis dumerilii (Pdum)-Post2 on cDNA from the tails of the juvenile worms P. dumerilii, and were convinced of their validity, since this gene is clearly transcribed at this stage (Supplementary Figure S4)
Platynereis dumerilii is an appropriate model object for evolutionary aspects of early development study. This is a spiralian animal with stereotypical cleavage, which is well traced at the single cells level

Summary

Introduction

Genome-wide studies that investigate developmental processes have shown thatMetazoan genomes are pervasively transcribed in oogenesis to create the complexity necessary for early development, that is, during the period when the zygotic genome is not yet working. Genome-wide studies that investigate developmental processes have shown that. Mammalian oocytes contain from 0.3 ng (mouse, human) to 2 ng (cow) of RNA, of which 10–15% are mRNAs [1,2,3]. A somatic cell contains only 10 to 30 pg of total RNA, depending on the type. Maternal factors of Drosophila (such as Nanos, Caudal, Bicoid, Hunchback) are at the top of the regulatory cascade that establishes, regionalizes, and patterns the anteroposterior axis of the embryo [4,5]. Pair-rule genes, segment polarity genes and Hox genes are under the direct or indirect control of these factors. The position of Hox genes within this regulatory hierarchy is several steps below that of maternal genes

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