High impact information on mab-5

• The activities of cell signals and pal-1 appear to influence V cell fates by determining the state of a developmental switch that involves two homeotic genes, lin-22 and mab-5 [1].
• This suggests that mab-5 influences cell differentiation and cell migration by regulating gene expression, and clearly demonstrates that genes containing homeoboxes influence global aspects of pattern formation in organisms other than Drosophila [2].
• We find that the pattern of fates specified by mab-5 not only depends on mab-5 expression but also on post-translational interactions with the neighboring HOM-C gene lin-39 and a second, inferred gene activity [3].
• We show here that in the P11 lineage, a complex between MAB-5 and the Pbx homolog CEH-20 directly regulates transcription of the BH3 domain gene egl-1 to initiate programmed cell death; in the P12 lineage, mab-5 and ceh-20 apparently act indirectly to initiate programmed cell death [4].
• In the nematode C. elegans, the Hox gene mab-5 is required for the programmed cell deaths of two lineally related cells generated in the P11 and P12 lineages [4].

Biological context of mab-5

• Within the posterior body region, mab-5 activity controls epidermal, neuronal, and mesodermal cell differentiation, and also the direction of cell migration [2].
• This suggests that posterior-specific expression of mab-5 depends on the appropriate segregation of developmental factors during early embryogenesis [5].
• We find that the C. elegans Antennapedia homolog, mab-5, sequentially programs many independent events within individual cell lineages [6].
• Mutations in the homeotic gene Ppa-mab-5 cause severe misspecification of the M lineage, resembling more the C. elegans Twist than the mab-5 phenotype [7].
• In C. elegans, two Hox genes, lin-39 and mab-5, control the cell fusion decision of the 12 ventrally located Pn.p cells [8].

Anatomical context of mab-5

• In these partial embryos, however, the fusion was often expressed in cells scattered throughout the embryo, suggesting that cell-cell interactions and/or proper positioning of early blastomeres are required for mab-5 expression to be localized to the posterior [5].
• By examining the M lineage and its differentiation products in different Hox mutant combinations, we found an essential but overlapping role for two of the Hox cluster genes, lin-39 and mab-5, in diversification of the postembryonic mesoderm [9].
• Furthermore, if lin-39 is replaced with the posterior Hox gene mab-5, then posterior structures are induced instead of a vulva [10].
• Expression of LIN-32 is spatially restricted by the combined action of the Hox gene mab-5 and the hairy homolog lin-22, while MAB-3 is expressed throughout the lateral hypodermis [11].
• Mutations in the C. elegans gene egl-27 cause defects in cell polarity and cell migration: the polarity of the asymmetric T cell division is disrupted and the descendants of the migratory QL neuroblast migrate incorrectly because they fail to express the Hox gene mab-5 [12].

Regulatory relationships of mab-5

• In anterior body regions, lin-22(+) inhibits expression of the Hox gene mab-5 [13].
• Unexpectedly, the lack of cell-cell contacts does not prevent a unique seam cell to produce a neuroblast, even though a homeotic gene (mab-5) that normally prevents the neuroblast commitment is ectopically expressed in the absence of nhr-25 function [14].

Other interactions of mab-5

• Here we report that egl-20, a C. elegans gene required to activate expression of the Hox gene mab-5 in the migratory neuroblast QL, encodes a member of the Wnt family of secreted glycoproteins [15].
• We have found that a second Wnt pathway gene, bar-1, which encodes a beta-catenin/Armadillo-like protein, is also required for activation of mab-5 expression in QL [15].
• The Caenorhabditis elegans lin-39, mab-5 and egl-5 Hox genes specify cell fates along the anterior-posterior body axis of the nematode during postembryonic development, but little is known about Hox gene functions during embryogenesis [16].
• We find that ceh-7 is not expressed in egl-5 mutants, but is still expressed in mab-5 mutants [17].
• These blocked embryos remain viable for days and express a number of biochemical markers of early differentiation, for example, gut granules, the gut esterase ges-1, and two regulatory genes, mab-5 and hlh-1 [18].

References