The first cleavage of C. elegans is asymmetric, generating daughter cells with different sizes, cytoplasmic components, and fates. Mutations in the par-1 gene disrupt this asymmetry. We report here that par-1 encodes a putative Ser/Thr kinase with similarity to kinases from yeasts and mammals. Two strong alleles have mutations in the kinase domain, suggesting that kinase activity is essential for par-1 function. PAR-1 protein is localized to the posterior periphery of the zygote and is distributed in a polar fashion preceding the asymmetric divisions of the germline lineage. Because PAR-1 distribution in the germline correlates with the distribution of germline-specific P granules, it is possible that PAR-1 functions in germline development as well as in establishing embryonic polarity.

SummaryInitiation and maintenance of infection by mycobacteria in susceptible hosts are not well understood. A screen of Mycobacterium marinum transposon mutant library led to isolation of eight mutants that failed to cause haemolysis, all of which had transposon insertions in genes homologous to a region between Rv3866 and Rv3881c in Mycobacterium tuberculosis , which encompasses RD1 ( Rv3871-Rv3879c ), a known virulence gene cluster. The M. marinum mutants showed decreased virulence in vivo and failed to secrete ESAT-6, like M. tuberculosis RD1 mutants . M. marinum mutants in genes homologous to Rv3866-Rv3868 also failed to accumulate intracellular ESAT-6, suggesting a possible role for those genes in synthesis or stability of the protein. These transposon mutants and an ESAT-6 / CFP-10 deletion mutant all showed reduced cytolysis and cytotoxicity to macrophages and significantly decreased intracellular growth at late stages of the infection only when the cells were infected at low multiplicity of infection, suggesting a defect in spreading. Direct evidence for cell-to-cell spread by wild-type M. marinum was obtained by microscopic detection in macrophage and epithelial monolayers, but the mutants all were defective in this assay. Expression of M. tuberculosis homologues complemented the corresponding M. marinum mutants, emphasizing the functional similarities between M. tuberculosis and M. marinum genes in this region that we designate extRD1 (extended RD1). We suggest that diminished membranolytic activity and defective spreading is a mechanism for the attenuation of the extRD1 mutants. These results extend recent findings on the genomic boundaries and functions of M. tuberculosis RD1 and establish a molecular cellular basis for the role that extRD1 plays in mycobacterial virulence. Disruption of the M. marinum homologue of Rv3881c , not previously implicated in virulence, led to a much more attenuated phenotype in macrophages and in vivo , suggesting that this gene plays additional roles in M. marinum survival in the host.

The par-3 gene is required for establishing polarity in early C. elegans embryos. Embryos from par-3 homozygous mothers show defects in segregation of cytoplasmic determinants and in positioning of the early cleavage spindles. We report here that the PAR-3 protein is asymmetrically distributed at the periphery of the zygote and asymmetrically dividing blastomeres of the germline lineage. The PAR-3 distribution is roughly the reciprocal of PAR-1, another protein required for establishing embryonic polarity in C. elegans. Analysis of the distribution of PAR-3 and PAR-1 in other par mutants reveals that par-2 activity is required for proper localization of PAR-3 and that PAR-3 is required for proper localization of PAR-1. In addition, the distribution of the PAR-3 protein correlates with differences in cleavage spindle orientation and suggests a mechanism by which PAR-3 contributes to control of cleavage pattern.

Zebrafish as a neurogenetic model system depends on the correct neuroanatomical understanding of its brain organization. Here, we address the unresolved question regarding a possible zebrafish homologue of the dorsal pallial division, the region that in mammals gives rise to the isocortex. Analyzing the distributions of nicotine adenine dinucleotide phosphate diphorase (NADPHd) activity and parvalbumin in the anterior zebrafish telencephalon, we show that against previous assumptions the central (Dc) zone possesses its own germinative region in the dorsal proliferative zone. We define the central (Dc) zone as topologically corresponding to the dorsal pallial division of other vertebrates (mammalian isocortex). In addition, we confirm through BrdU-labeling experiments that the posterior (Dp) zone is formed by radial migration and homologous to the mammalian piriform cortex. Based on our results, we propose a new developmental and organizational model of the zebrafish pallium-one which is the result of a complex outwardinward folding.

We examined the brain expression patterns of zebrafish genes Lhx6, Lhx7, Dlx2a, GAD67, and Tbr2/eomesa; except for GAD67, expression domains are restricted to the forebrain. In particular, a distribution of transcripts in the early zebrafish telencephalon comparable to that of tetrapods is revealed. Expression domains of Lhx6 and Lhx7 are restricted to a ventral subdivision (Sdv) of the precommissural dorsal subpallium, interpreted here as the homologue of the mammalian medial ganglionic eminence (the adult pallidum in mammals). In contrast, there is no such expression in the dorsal subdivision (Sdd) of the dorsal subpallium, interpreted here as the homologue of the mammalian lateral ganglionic eminence (the adult caudatoputamen in mammals). The Lhx6 and Lhx7 genes are furthermore expressed in the zebrafish ventral subpallium (Sv, septum), and in the supra-/postcommissurally lying posterior subdivision of the dorsal subpallium (Sdp; possible homologue of the subpallial amygdala). Also in support of this comparative interpretation, Dlx2a is generally expressed in all of the subpallium, including the ventricular zones of (all three subvidisions of) the dorsal as well as of the ventral subpallium. In contrast, Tbr2 is expressed in all of the zebrafish pallium and in a restricted zone of the ventral subpallium, comparable to the known restricted septal expression in mammals. The telencephalic expression of GAD67 largely coincides with that of Dlx2a. However, GAD67-positive cells migrate (radially) into postmitotic zones of the peripheral subpallium (as does Dlx2a and Lhx6) as well as (tangentially) into pallial zones (as does Dlx2a, but not Lhx6).