Biology subjects

Gert, K. R.

Publications and source records attributed to Gert, K. R..

5 recordsLinked to original sources

bioRxiv2021

Reciprocal zebrafish-medaka hybrids reveal maternal control of zygotic genome activation timing

The sperm and egg contribute unequally to the newly formed zygote. While the sperm provides mainly paternal DNA, the egg provides both maternal DNA and the bulk of the future embryonic cytoplasm. Most embryonic processes like the onset of zygotic transcription are thought to depend on maternal cytoplasmic components, but this has not been tested rigorously. Here we report the establishment of a reciprocal zebrafish-medaka hybrid system which enables unequivocal distinction between maternal and paternal gene products. By combining expression of zebrafish Bouncer on the medaka egg with artificial egg activation, we demonstrate the in vitro generation of paternal zebrafish/maternal medaka (reripes) hybrid embryos. These hybrids complement the previously reported paternal medaka/maternal zebrafish (latio) hybrid embryos1, providing a versatile tool to dissect parental control mechanisms during early development. With this system, we investigated maternal vs. paternal control of zygotic genome activation (ZGA) timing. RNA-seq and ATAC-seq analyses of the purebred fish species and hybrids revealed that the onset of ZGA is primarily governed by the egg. Combining these datasets with proteome-wide analysis of early medaka and zebrafish embryogenesis highlights new potential regulators of ZGA, including Znf281b. Overall, our study establishes the reciprocal zebrafish-medaka hybrid system as a versatile tool to study parent-of-origin effects in vertebrate embryos.

developmental biology↗

bioRxiv2021

Maternally-inherited anti-sense piRNAs antagonize transposon expression in teleost embryos

Transposable elements threaten genome stability, and the Piwi-piRNA system has evolved to silence transposons in the germline1-6. However, it remains largely unknown what mechanisms are utilized in early vertebrate embryos prior to germline establishment and ping-pong piRNA production. To address this, we first characterized small RNAs in early zebrafish embryos and detected abundant maternally-deposited, Ziwi-associated, antisense piRNAs that map largely to evolutionarily young long terminal repeat (LTR) retrotransposons. Notably, the focal establishment of the repressive modification H3K9me2/3 coincides with these young LTR elements, is deposited independent of transcription, and is required for LTR silencing. We find piRNAs highly enriched and maintained in primordial germ cells (PGCs), which display lower LTR expression than somatic cells. To examine the consequences of piRNA loss, we used reciprocal zebrafish-medaka hybrids, which display selective activation of LTRs that lack maternally-contributed targeting piRNAs. Thus, the Piwi-piRNA system actively antagonizes transposons in the soma and PGCs during early vertebrate embryogenesis.

developmental biology↗

bioRxiv2021

SCON - A Short Conditional intrON for conditional knockout with one-step zygote injection

The generation of conditional alleles using CRISPR technology is still challenging. Here, we introduce a Short Conditional intrON (SCON, 189 bp) that enables rapid generation of conditional alleles via one-step zygote injection. SCON has conditional intronic function in various vertebrate species and its target insertion is as simple as CRISPR/Cas9-mediated gene tagging.

genetics↗

bioRxiv2021

Sperm membrane proteins DCST1 and DCST2 are required for the sperm-egg fusion process in mice and fish

The process of sperm-egg fusion is critical for successful fertilization, yet the underlying mechanisms that regulate these steps have remained unclear in vertebrates. Here, we show that both mouse and zebrafish DCST1 and DCST2 are necessary in sperm to fertilize the egg, similar to their orthologs SPE-42 and SPE-49 in C. elegans and Sneaky in D. melanogaster. Mouse Dcst1 and Dcst2 single knockout (KO) spermatozoa are able to undergo the acrosome reaction and show normal relocalization of IZUMO1, an essential factor for sperm-egg fusion, to the equatorial segment. While both single KO spermatozoa can bind to the oolemma, they rarely fuse with oocytes, resulting in male sterility. Similar to mice, zebrafish dcst1 KO males are subfertile and dcst2 and dcst1/2 double KO males are sterile. Zebrafish dcst1/2 KO spermatozoa are motile and can approach the egg, but rarely bind to the oolemma. These data demonstrate that DCST1/2 are essential for male fertility in two vertebrate species, highlighting their crucial role as conserved factors in fertilization.

developmental biology↗

bioRxiv2018

The Ly6/uPAR protein Bouncer is necessary and sufficient for species-specific fertilization

Fertilization is fundamental for sexual reproduction, yet its molecular mechanisms are poorly understood. Here, we identify an oocyte-expressed Ly6/uPAR protein, which we call Bouncer, as a crucial fertilization factor in zebrafish. We show that membrane-bound Bouncer mediates sperm-egg binding and is thus essential for sperm entry into the egg. Remarkably, Bouncer is not only required for sperm-egg interaction, but also sufficient to allow cross-species fertilization between zebrafish and medaka, two fish species that diverged over 150 million years ago. Our study thus identifies Bouncer as a key determinant of species-specific fertilization in fish. Bouncers closest homolog in tetrapods, SPACA4, is restricted to the male gonad in internally fertilizing vertebrates, suggesting that our findings in fish have relevance to human biology.

developmental biology↗