... events in embryos of the glossiphoniid leech Helobdella robusta (phylum Annelida). As representatives of the proposed super-phylum Lophotrochozoa , glossiphoniid leeches are of interest for developmental and evolutionary comparisons. Their embryos are suitable for microinjection, but no genetic...

... and the dorsolateral P lineage differ to some degree in distantly related clitellate species such as the leeches Helobdella and Theromyzon , and the sludgeworm Tubifex . To examine this developmental variation at a lower taxonomic level, we have explored the specification pathways of the O and P lineages in the leech...

...Daniel H. Shain; Duncan K. Stuart; Françoise Z. Huang; David A. Weisblat The leech nervous system comprises a relatively simple network of longitudinal (connective) and transverse (segmental) nerves. We have followed the normal pattern of axon development in the glossiphoniid leech Theromyzon rude...

...Dian-Han Kuo; Marty Shankland Despite a high degree of homonomy in the segmental organization of the ectoderm, the body plan of the leech is divided into two zones based on the distinct cell lineage patterns that give rise to the O/P portion of the segmental ectoderm. In the midbody and caudal...

...Mi Hye Song; Françoise Z. Huang; Gwendolen Y. Chang; David A. Weisblat We have identified homologs of the Drosophila pair-rule gene even-skipped in the glossiphoniid leeches Helobdella robusta and Theromyzon trizonare . In leech embryos, segments arise sequentially from five pairs of embryonic...

...Françoise Z. Huang; Dongmin Kang; Felipe-Andres Ramirez-Weber; Shirley T. Bissen; David A. Weisblat In leech embryos, segmental mesoderm and ectoderm arise from teloblasts by lineages that are already relatively well characterized. Here, we present data concerning the early divisions...

...Elaine C. Seaver; Marty Shankland ABSTRACT The segmented ectoderm and mesoderm of the leech arise via a stereotyped cell lineage from embryonic stem cells called teloblasts. Each teloblast gives rise to a column of primary blast cell daughters, and the blast cells generate descendant clones...

...Daniel H. Shain; Duncan K. Stuart; Françoise Z. Huang; David A. Weisblat Central nervous system (CNS) in leech comprises segmentally iterated progeny derived from five embryonic lineages (M, N, O, P and Q). Segmentation of the leech CNS is characterized by the formation of a series of transverse...

... precursor cells of the glossiphoniid leech Helobdella robusta . We find that this fusion event is regulated inductively by a cell that does not itself fuse. We also show that biochemical arrest (by microinjection with ricin A chain or ribonuclease A) of the inducer or either of the fusion partners prevents...

...Marc Pilon; David A. Weisblat ABSTRACT From the glossiphoniid leech Helobdella robusta , we have cloned and determined the complete coding sequence of Hro-nos , a gene homologous to the nanos gene from Drosophila melanogaster . Developmental northern blots show that Hro-nos , like nanos...

...Constance M. Smith; Deborah Lans; David A. Weisblat ABSTRACT Gastrulation in leech embryos is dominated by the epibolic movements of two tissues: germinal bands, composed of segmental precursor cells, and an overlying epithelium that is part of a provisional integument. During gastrulation...

...Françoise Z. Huang; David A. Weisblat ABSTRACT In embryos of glossiphoniid leeches such as Helobdella triserialis and H. robusta , pairs of adjacent ‘o/p’ ectodermal blast cells are known to be developmentally equipotent and yet eventually contribute distinct sets of ‘O’ and ‘P’ progeny...

...Felipe-Andrés Ramírez; Cathy J. Wedeen; Duncan K. Stuart; Deborah Lans; David A. Weisblat ABSTRACT In embryos of leeches (phylum Annelida), metameric structures arise sequentially from a germinal plate comprising the descendants of five pairs of embryonic stem cells called teloblasts. It has been...

...Denise Nardelli-Haefliger; Ashley E. E. Bruce; Marty Shankland ABSTRACT The homeobox gene Lox2 , a member of the HOM/Hox gene class, is expressed in a restricted domain along the anteroposterior (A-P) body axis of the leech Helobdella . The segmental tissues of the leech embryo arise from...

...Denise Nardelli-Haefliger; Marty Shankland ABSTRACT A novel leech homeobox gene, Lox10 , is shown to encode a homeodomain sequence characteristic of a phyletically widespread NK-2 homeobox gene class. Lox10 expression was examined in leech embryos of various ages by in situ hybridization...

...Deborah Lans; Cathy J. Wedeen; David A. Weisblat ABSTRACT ht-en is an engrailed -class gene that is expressed during early development and neurogenesis in embryos of the leech Helobdella triserialis . During the early development of this annelid (stages 7-9), ht-en is expressed in each...

...Tom Becker; Eduardo R. Macagno ABSTRACT Most midbody ganglia in the central nervous system (CNS) of the leech Hirudo medicinalis contain about 400 neurons. However, those in the fifth and sixth midbody segments (ganglia M5 and M6) are specialized for reproductive functions, and each contain several...

...Cathy J. Wedeen; David A. Weisblat ABSTRACT ht-en protein, an annelid homolog of the Drosophila engrailed protein, is expressed during both early development and neurogenesis in embryos of the leech, Helobdella triserialis . In Helobdella as in Drosophila , early expression is in segmentally...

...Steven A. Torrence ABSTRACT The stereotyped distribution of identified neurons and glial cells in the leech nervous system is the product of stereotyped cell migrations and rearrangements during embryogenesis. To examine the dependence of longdistance cell migrations on positional cues provided...

...Shirley T. Bissen; David A. Weisblat When tritiated thymidine triphosphate ([ 3 H]TTP) or its immunohistochemically detectable analogue, bromodeoxyuridine triphosphate (BrdUTP), is injected into blastomeres of leech embryos it passes throughout the entire embryo and is rapidly incorporated (within...