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Reposted by Sheri

Arjuna Rajakumar PhD @arjunarajakumar.bsky.social · 19/09/2026

Always a pole cell never a pgc! Transcription may be essential to segregate healthy and defective pole cells. Pole cells that never activate their zygotic genome and retain what mommy gave them, die. Pole cells that activate their zygotic genome too much also die. Life is a balance! 8/8

Stage 10b embryo highlighting our two populations of germ cells, ones that retain a maternal transcriptome (yellow) and ones that activate zygotically (magenta)

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Reposted by Sheri

Arjuna Rajakumar PhD @arjunarajakumar.bsky.social · 19/09/2026

Lost children are the first germ cells to die during embryogenesis, they fail to undergo trans-epithelial migration and are lost in the gut. When we rescue their death with chk2 mutants they still retain maternal transcripts and do not express zygotic transcripts. 7/8

Stage10 b embryos showing two clusters of germ cells, ones with low level expression of the maternal transcript pgc (yellow) and ones with high. Using gut markers we find these high pgc germ cells remain stuck in the posterior midgut

Lost children die between stage 9-11, when we rescue their death using chk2 mutants HR-mediated cell death, we can rescue the lost children death. However, these germ cells still retain maternal transcripts when their successfully migrating counterparts do not!

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Reposted by Sheri

Arjuna Rajakumar PhD @arjunarajakumar.bsky.social · 19/09/2026

Finally, our data uncovered a second unexpected cluster of germ cells that we term lost children. These germ cells are isolated from the 9 to 12 hour AEL window as coalesced germ cells. These germ cells completely retain their maternal transcriptome and never activate zygotic gene expression. 6/8

Batch correction of scRNA-seq data using Harmony results in the lost children clustering within the early timepoints, indicating that their transcriptome resembles that of newly formed germ cells despite their late developmental stage.

Feature plots of nanos and amos expression on the Harmony batch-corrected UMAP. Despite their late developmental age, the lost children nestle among the early timepoint germ cells, retaining the maternal transcript nanos. However, unlike the surrounding germ cells, the lost children do not express the Class II gene amos.

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Reposted by Sheri

Arjuna Rajakumar PhD @arjunarajakumar.bsky.social · 19/09/2026

As It turns out, nanos actually inhibits Zelda protein levels in pole cells! Now we find that pole cells in nanos mutants have a dramatic increase in Zelda protein. Nanos -> Zelda -> class II genes. This sheds new light for how nanos protects germline identity and prevents its somatization. 5/8

Top panels: nanos heterozygotes showing limited levels of Zelda protein in pole cells.
Bottom panels: nanos mutants showing increased levels of Zelda protein in pole cells, veering into soma level territory!

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Reposted by Sheri

Arjuna Rajakumar PhD @arjunarajakumar.bsky.social · 19/09/2026

We found that while these class II genes are expressed in pole cells, their translation is inhibited by nanos. Unexpectedly, when we examined class II transcription in nanos mutants we found a dramatic increase in their transcription!! 4/8

Top panels: Control embryos showing that translation of the class II gene Amos is limited to a handful of pole cells.
Bottom panels: nanos mutant embryos showing a significant increase in Amos translation

top panels: nanos heterozygous embryos (controls) showing limited early transcription of the class II genes elba1 and sisA (gcl is a germline marker mark the pole cells)
bottom panels: nanos mutants showing dramatic increase in the levels of class II transription

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Reposted by Sheri

Arjuna Rajakumar PhD @arjunarajakumar.bsky.social · 19/09/2026

Instead, their transcription is dependent on the pioneer factor #Zelda, where loss of Zelda results in loss of early pole cell transcription. 3/8

Images showing Zelda protein expression in stage 4 pole cells

Top panels show control embryos zygotic transcription in the germ cells
Bottom panels show Zelda RNAi which results in loss of pole cell transcription

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Sheri @sagrill.bsky.social · 19/09/2026

This work would not have been possible without the incredible snATAC-seq atlas of the Drosophila embryo from @diegoisworking.bsky.social @jshendure.bsky.social and @eileen-furlong.bsky.social which helped us discover that germ cells retain a totipotent chromatin state throughout development!

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Sheri @sagrill.bsky.social · 19/09/2026

Thank you @arjunarajakumar.bsky.social Couldn't have done it without you!

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Sheri @sagrill.bsky.social · 19/09/2026

Incredibly excited to share my new preprint! 🪰🧬 Ever wondered how germ cells can specify their fate without having a dedicated transcriptional program? We found that germ cells keep the uncommitted chromatin state of the early embryo www.biorxiv.org/content/10.6...

biorxiv.org

Decoupling Transcription from Cell Fate Preserves Germ Cell Totipotency

Only germ cells can give rise to a totipotent embryo, yet a conserved transcriptional program for germ cell identity remains elusive. Profiling Drosophila primordial germ cells (PGCs) across embryogen...

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