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Segment number threshold determines juvenile onset of germline cluster expansion in <i>Platynereis dumerilii</i>

202 Citations2021
E. Wolfgang Kuehn, David S. Clausen, Ryan W. Null

Molecular analyses suggest a previously unidentified developmental transition dependent on the growth state of juvenile P. dumerilii leading to substantially increased germline expansion.

Abstract

<jats:title>Abstract</jats:title> <jats:p> Development of sexual characters and generation of gametes are tightly coupled with growth. <jats:italic>Platynereis dumerilii</jats:italic> is a marine annelid that has been used to study germline development and gametogenesis. <jats:italic>P. dumerilii</jats:italic> has germ cell clusters found across the body in the juvenile worms, and the clusters eventually form the gametes. Like other segmented worms, <jats:italic>P. dumerilii</jats:italic> grows by adding new segments at its posterior end. The number of segments reflect the growth state of the worms and therefore is a useful and measurable growth state metric to study the growth‐reproduction crosstalk. To understand how growth correlates with progression of gametogenesis, we investigated germline development across several developmental stages. We discovered a distinct transition period when worms increase the number of germline clusters at a particular segment number threshold. Additionally, we found that keeping worms short in segment number, by manipulating environmental conditions or via amputations, supported a segment number threshold requirement for germline development. Finally, we asked if these clusters in <jats:italic>P. dumerilii</jats:italic> play a role in regeneration (as similar free‐roaming cells are observed in <jats:italic>Hydra</jats:italic> and planarian regeneration) and found that the clusters were not required for regeneration in <jats:italic>P. dumerilii</jats:italic> , suggesting a strictly germline nature. Overall, these molecular analyses suggest a previously unidentified developmental transition dependent on the growth state of juvenile <jats:italic>P. dumerilii</jats:italic> leading to substantially increased germline expansion. </jats:p>