Elsevier

Developmental Biology

Volume 300, Issue 1, 1 December 2006, Pages 406-415
Developmental Biology

Germ line determinants are not localized early in sea urchin development, but do accumulate in the small micromere lineage

https://doi.org/10.1016/j.ydbio.2006.07.035Get rights and content
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Abstract

Two distinct modes of germ line determination are used throughout the animal kingdom: conditional—an inductive mechanism, and autonomous—an inheritance of maternal factors in early development. This study identifies homologs of germ line determinants in the sea urchin Strongylocentrotus purpuratus to examine its mechanism of germ line determination. A list of conserved germ-line associated genes from diverse organisms was assembled to search the S. purpuratus genome for homologs, and the expression patterns of these genes were examined during embryogenesis by whole mount in situ RNA hybridization and QPCR. Of the 14 genes tested, all transcripts accumulate uniformly during oogenesis and Sp-pumilio, Sp-tudor, Sp-MSY, and Sp-CPEB1 transcripts are also uniformly distributed during embryonic development. Sp-nanos2, Sp-seawi, and Sp-ovo transcripts, however, are enriched in the vegetal plate of the mesenchyme blastula stage and Sp-vasa, Sp-nanos2, Sp-seawi, and Sp-SoxE transcripts are localized in small micromere descendents at the tip of the archenteron during gastrulation and are then enriched in the left coelomic pouch of larvae. The results of this screen suggest that sea urchins conditionally specify their germ line, and support the hypothesis that this mechanism is the basal mode of germ line determination amongst deuterostomes. Furthermore, accumulation of germ line determinants selectively in small micromere descendents supports the hypothesis that these cells contribute to the germ line.

Keywords

Sea urchin
Germ line
Small micromeres
Deuterostome
Nanos
Vasa
DMRT
Mago nashi
Pumilio
Piwi
SoxE
Tudor
Boule
Germ cell-less
MSY
CPEB
Ovo
MORC

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