title: A member of the six gene family promotes the specification of P cell fates in the O/P equivalence group of the leech Helobdella.
abstract: The lateral ectoderm of the leech embryo arises from the o and p bandlets, two parallel columns of blast cells that collectively constitute the O/P equivalence group. Individual blast cells within this equivalence group become committed to alternative O or P developmental pathways in accordance with their respectively ventrolateral or dorsolateral position (Weisblat and Blair, 1984). We here describe a novel member of the Six gene transcription factor family, Hau-Six1/2A, which contributes to the patterning of these cell fates in the leech Helobdella sp. (Austin). During embryogenesis Hau-Six1/2A expression is restricted to the dorsolateral column of p blast cells, and thus correlates with P cell fate over most of the body's length. Experimental manipulations showed that Hau-Six1/2A expression is induced in p blast cells by the interaction with the adjoining q bandlet. In addition, misexpression of Hau-Six1/2A in the ventrolateral o blast cells by injection of an expression plasmid elicited the dorsolateral P cell fates ectopically. These data imply that Hau-Six1/2A is a component of the molecular pathway that normally distinguishes O and P cell fates within this equivalence group. Genomic analysis revealed that the Six1/2 subfamily has expanded to a total of six genes in Helobdella. The pattern of Hau-Six1/2A expression during later embryogenesis suggested that this gene may have lost ancestral function(s) and/or acquired novel roles in association with the gene duplications that produced this expansion.
authors.affiliation: Section of Molecular Cell and Developmental Biology and Institute of Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Ian K
authors.initials: IK
authors.lastname: Quigley
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Schmerer
authors.forename: Marty
authors.initials: M
authors.lastname: Shankland
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019070:Cell Lineage; D015509:Developmental Biology; D004475:Ectoderm / Q000378:metabolism; D004625:Embryo, Nonmammalian; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D007865:Leeches / Q000235:genetics* / Q000502:physiology*; D008953:Models, Anatomic; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D005810:Multigene Family; D017386:Sequence Homology, Amino Acid