Developnient 245-260 (1937) Prted 245 Biologat Orcat Bulilin TJC ( upiny UMiicd [467 Determinative properties of muscle lineages in ascidian embryos THOMAS H MEEDEL , ROBERT CROWTHER and R. WHITTAKER Laburatory Developmtental Genetics, Biological ! aborator} Morje Huk Wond 02545. USA Minger usert Summary Blastomeres removed from early cleavage stage differences also occurred the   time  acetylcholin- cmbryos and reared to "maturity' cIdian partial esterasc activity was first detected partial cinbryos elaborate tissue-specific leatures typi- oftet embryus from these [WO Isolated bA.2 SOurCCC cells failed to their  constituent cell lineages. We used  this show muscle development even in combination pruperty study recent corrections of the ascidian with anterior-animal cells (44.2 and are presumably linenge larval Inuscle and to compare the ways in even dependent normal cell interactions and mort lineages   give rise #hich   different muscle. (ur associations Others have noted an additional distine- differentiation musclc evaimanon #as   based on tion between the different sources of muscle: muscle histochemical localizalion and quantitative radio cells from non-B4.1 lineages occur exclusively in thc metric measurement of muscl ~specific acetylchol- distal BL part the tail, while   the desccndants inesterase activity and lhe development of myofila- contribute those   cells   in and proximal middle ments and myofibrils observed electron regions. During the course of ascidlian larval evolution microscopy. Although the  posterior-vegetal blasto probably had nlece Jwo origins: the primary meres (B4. embryo pair) of the &-cell hare lincage (B4.L) long been Ghose fate rigidly at early believed to be the sole precursors of Iarval muscle. clcaage stuges and stcondarily evolved   lineages Sludies rocent using horseradish peroxidase mark which arose later by recruitment of cells from other cell lineages have shown that small numbcrs of muscle lissues resulting in increased tail length. In contrast to cells originate fromn the anterior linenge. egetal (A4.1) the B4. muscle developient in the second- (64.2) blastomeres posleriur-animal or   this   stage. ary lineages cuntrolled less rigidly by proresses that Fully differentiated muscle cxpression isolated depend par- cell interactions tial embryos of A4.1-derived cells requires an assaci- ation with cells other lineages whereas muscle Fruni Kcy words: ascidian , muscle , cell lincage Ciona from BA blastorneres develops autonomously Clear infestinalis Ascidia ceratodes. Introduction shuped Iegion of yellow cytoplasm in the fertilized egg of Styela parita noted the segregation of this und In the decade past there has bcen yellow cytoplasm into the presumptive tail rcsurgence of muscle research interest in the cell lineages of several animal cells of the embryo The developmental autonom} allempr species in detine the various mechan- findings implied by his Iater connrmed in histo establishing cell commnitments iSIS thar operate in logical investigations notably by Reverberi & miosi uring embryogenests Considerable differences CC- Minganti (1946_ 1947): isolation of BA [ Iwo cur lime at which embryonic of  the Ceus blastomeres from the 8-cell Stage _ into which most of particulr iiedel organisms chosen first establish the milochondria-enriched yellow crescent malerial "clones' of invariant cell fate; these studies have been bccvmes segregated, rcsulted partial embryos con- subject number of rccent revicws (e taining differentiated muscle cells. Other blastomere Davidson 1986 Slack 1983; Stent, 1985). Develop- isolates   did make obvious Muscle_ This "sell of larval tail muscle in ascidian MCM[ differentiation' haus also been demonstrated by the _ Temains embryos - thc clussic example vety early   and seemingly acetyleholinesterase culenee and myoflaments/ complere cell lineage determination. Conklin (19U5) myelibrils in B4. partial embryos ( Whittaker, Orto describcd detail  the occurrence FetTuzza- crescent- Iana Farinella 1977: Whittaker. 1982;
Developnient 245-260 (1937) Prted Orcat Bulilin TJC ( upiny Biologat UMiicd [467 245 Determinative properties of muscle lineages in ascidian embryos THOMAS H MEEDEL , ROBERT CROWTHER and R. WHITTAKER Laburatory Developmtental Genetics, Morje Biological ! aborator} Wond Huk Minger usert 02545. USA Summary Blastomeres removed from early cleavage stage differences also occurred cIdian cmbryos and reared to "maturity' the   time  acetylcholin- partial esterasc activity was first detected embryus oftet elaborate tissue-specific leatures typi- partial cinbryos from these [WO SOurCCC Isolated bA.2 cells failed to their  constituent cell lineages. We used  this show muscle development even in combination pruperty study recent corrections of the ascidian with anterior-animal cells (44.2 larval Inuscle and linenge are presumably and to compare the ways in even mort dependent #hich   different normal cell interactions and lineages   give rise muscle. (ur associations evaimanon Others have noted an additional distine- musclc differentiation #as   based on tion between the different histochemical sources of muscle: muscle localizalion and quantitative radio cells from non-B4.1 lineages occur exclusively in thc metric measurement of muscl ~specific acetylchol- distal part inesterase the tail, while   the BL activity desccndants and lhe development of myofila- contribute those   cells   in ments and myofibrils proximal and middle observed electron regions. During the course of ascidlian larval evolution microscopy. Although the  posterior-vegetal blasto nlece probably had Jwo meres (B4. origins: the primary pair) of the &-cell embryo hare long been lincage (B4.L) Ghose fate believed to be the sole precursors rigidly at early of Iarval muscle. clcaage stuges rocent and stcondarily Sludies evolved   lineages using horseradish peroxidase mark which arose later by recruitment of cells from other cell lineages have shown that small numbcrs of muscle lissues resulting in increased tail length. In contrast to cells originate fromn the anterior egetal (A4.1) the B4. linenge. posleriur-animal muscle developient in the second- (64.2) blastomeres or   this   stage. ary lineages cuntrolled Fully differentiated less rigidly by proresses that muscle cxpression isolated par- depend cell interactions tial embryos of A4.1-derived cells requires an assaci- ation with cells Fruni other lineages whereas muscle Kcy words: ascidian , from BA blastorneres muscle , cell lincage Ciona develops autonomously Clear infestinalis Ascidia ceratodes. Introduction shuped Iegion of yellow cytoplasm in the fertilized egg of Styela parita und In the decade noted the segregation of this past there has bcen rcsurgence of yellow cytoplasm into the presumptive tail muscle research interest in the cell lineages of several animal cells of the embryo The species in developmental autonom} allempr detine the various mechan- implied by his findings iSIS thar operate in Iater connrmed in histo establishing cell commnitments logical investigations miosi uring notably by Reverberi & embryogenests Considerable differences CC- Minganti (1946_ cur 1947): isolation of lime at which Iwo BA [ embryonic Ceus of  the blastomeres from the 8-cell particulr iiedel Stage _ into which most of organisms chosen first establish the milochondria-enriched yellow crescent malerial "clones' of invariant cell fate; these studies have been bccvmes subject segregated, rcsulted partial embryos con- number of rccent revicws (e taining differentiated muscle cells. Davidson 1986 Slack Other blastomere 1983; Stent, 1985). Develop- isolates   did MCM[ make obvious of larval tail muscle in ascidian Muscle_ This "sell embryos - Temains thc differentiation' haus also been demonstrated by the _ clussic example vety early   and seemingly culenee acetyleholinesterase and myoflaments/ complere cell lineage determination. Conklin (19U5) myelibrils in B4. describcd partial embryos ( Whittaker, Orto detail  the occurrence crescent- Iana Farinella FetTuzza- 1977: Whittaker. 1982;