title: Germ line determinants are not localized early in sea urchin development, but do accumulate in the small micromere lineage.
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.
authors.affiliation: Department of Molecular and Cell Biology and Biochemistry, Brown University, 69 Brown Street, Providence, RI 02912, USA.
authors.forename: Celina E
authors.initials: CE
authors.lastname: Juliano
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Voronina
authors.forename: Christie
authors.initials: C
authors.lastname: Stack
authors.forename: Maryanna
authors.initials: M
authors.lastname: Aldrich
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Cameron
authors.forename: Gary M
authors.initials: GM
authors.lastname: Wessel
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D004625:Embryo, Nonmammalian / Q000502:physiology; D047108:Embryonic Development / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental; D008297:Male; D009693:Nucleic Acid Hybridization; D009866:Oogenesis / Q000235:genetics*; D010063:Ovum / Q000502:physiology*; D016133:Polymerase Chain Reaction; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012617:Sea Urchins / Q000235:genetics / Q000254:growth & development*; D013094:Spermatozoa / Q000502:physiology*
chemical_list: D017931:DNA Primers; D012313:RNA