Localization of murine HLH gene NSCL to chromosome 1 by use of recombinant inbred strains

Sequence and expression analysis of Nhlh1: a basic helix-loop-helix gene implicated in neurogenesis

Nhlh1 is a basic helix-loop-helix (bHLH) gene that has been implicated in mouse neurogenesis. Previous studies have shown it to be expressed in regions in which there are differentiating neurons during late embryonic and fetal development, but detailed studies of the role of Nhlh1 earlier in embryonic development have not been performed. In this paper, we examine the expression of Nhlh1 transcripts at early embryonic stages (E8.5-E10.5), at the onset of neurogenesis, and compare the pattern of expression with that of Islet-1, a marker of postmitotic neurons. We show that Nhlh1 is expressed in early postmitotic neurons but is down-regulated as these cells migrate from the ventricular zone. We have also determined the genomic structure of mouse Nhlh1 and have characterised the promoter sequence, as a first step towards identifying factors that may control Nhlh1 expression. Nhlh1 has been implicated previously as a candidate for the neural tube defect mutant loop-tail (Lp); here, we present sequence and expression data indicating that Nhlh1 is unlikely to be responsible for the Lp mutation.

Nhlh1, a basic helix-loop-helix transcription factor, is very tightly linked to the mouse looptail (Lp) mutation

Looptail (Lp) is a mutation on the distal portion of mouse Chromosome (Chr) 1 that affects neurulation in mouse and is phenotypically expressed by appearance of an open neural tube along the entire antero-posterior axis of the embryo (craniorachischisis). Nhlh1, a member of the basic helix-loop-helix family of transcription factors, is expressed in the developing neural tube in structures affected by the Lp mutation and has been regionally assigned to the distal part of mouse Chr 1. Using a large panel of looptail animals from an (Lp/+ x SWR/J)F1 x SWR/J segregating backcross progeny, we have determined that Nhlh1 maps very close to Lp, with no recombinant detected in 500 informative animals tested; both map within a 0.6-cM segment defined as D1Mit113/Apoa2/Fcer1 gamma-(0.4 cM)-Nhlh1/Lp-(0.2 cM)-Fcer1 alpha/D1Mit149/Spna1. Nucleotide sequencing of Nhlh1 cDNA clones from wild type (WT) and Lp/Lp embryos failed to identify sequence alterations associated with the mutant phenotype. Southern hybridization of genomic DNA from WT and Lp/Lp embryos failed to identify specific rearrangements at or near the Nhlh1 locus, and Northern RNA blotting and RT-PCR evaluation of Nhlh1 mRNA expression indicated that both the levels and types of Nhlh1 mRNAs produced in WT and Lp/Lp embryos were indistinguishable. These studies suggest that Nhlh1 and Lp are not allelic. Nevertheless, Nhlh1 is the Chr 1 marker most tightly linked to Lp identified to date and can, therefore, be used as an excellent entry probe to clone the Lp region.

Genetic basis of neural tube defects: the mouse gene loop-tail maps to a region of chromosome 1 syntenic with human 1q21-q23

A genetic basis for neural tube defects (NTD) is rarely doubted, but the genes involved have not yet been identified. This is partly due to a lack of suitable families on which to perform linkage analysis. An alternative approach is to use the many mouse genes that cause NTD as a means of isolating their human homologues. Loop-tail (Lp) is a semidominant mouse gene that, in homozygous mutants, causes the severe NTD phenotype cranio-rachischisis. As a first step toward cloning Lp, we have performed linkage analysis on an intraspecific backcross, using microsatellite and RFLP DNA markers. This study has localized Lp to a region of approximately 1.46 cM on mouse chromosome 1, flanked by the gene for the alpha chain of high-affinity Fc receptor for IgE (Fcer1 alpha) and a microsatellite repeat D1Mit113. Physical mapping data in the region suggest that the interval is likely to be no more than 1.8 Mb in size. The localization is several centimorgans distal to that previously assigned by linkage studies with biochemical and visible markers and suggests that the human homologue of Lp is likely to reside in a region of conserved homology on 1q21-q23.

Cloning and expression of the mouse laminin gamma 2 (B2t) chain, a subunit of epithelial cell laminin

We have isolated and sequenced the full-length cDNA for the mouse laminin gamma 2 chain and mapped it to mouse Chromosome 1 proximal to laminin gamma 1. The mRNA for the mouse gamma 2 spans 5.2 kb and codes for a 1192-residue amino acid polypeptide. The gamma 2 chain (formerly termed laminin B2t), a homologue of gamma 1 (formerly B2), lacks an N-terminal domain and has a shorter domain III in comparison to the laminin gamma 1 chain. The expression of the laminin gamma 2 and gamma 1 chains in both newborn and fetal mice was examined by both Northern analysis and in situ hybridization. mRNA for the laminin gamma 2 chain was expressed specifically by epithelial cells in many tissues with a particularly high level of expression in the tongue, hair follicles, lung and kidney. In contrast, a high level of expression of the laminin gamma 1 chain mRNA was seen in both epithelial and endothelial cells in these tissues. In addition, gamma 1 mRNA was expressed in other tissues such as the nasal septum, blood vessels, and the muscle of the tongue. Immunohistochemistry with an anti-gamma 2 IgG detected strong expression of the laminin gamma 2 chain in the basement membrane of the collecting tubules of the kidney and of the pancreas. Immunoprecipitation studies with antibodies to the gamma 2 chain detected three species at 165, 155 and 140 kDa in HT-1080 cell-conditioned media. This protein complex is characteristic of the kalinin (nicein/epiligrin) complex, and provides further evidence that these proteins are identical and that the gamma 2 chain is the subunit of the epithelial-cell-specific laminin.