Disease relevance of Fmn1

• In this region, there are two possible candidate genes, Wilms' tumor 1 and formin, that play important roles in kidney development [1].
• The peptide ligands were previously identified in immune responses to cytomegalovirus or lymphochoriomeningitis virus as immunodominant, optimally sized, and Ld restricted [2].
• In situ hybridization of a biotinylated probe on mouse chromosomes showed that the Ld transgene was located in the E area of chromosome 6 with which no genetic linkage to insulin-dependent diabetes mellitus was demonstrated [3].
• Mapping of the formin gene and exclusion as a candidate gene for the autosomal recessive form of limb-girdle muscular dystrophy [4].
• Although human adenovirus 12 can suppress endogenous class I genes, it cannot down-regulate the activity of the transiently transfected cat gene which has been placed under the control of the Ld enhancer and promoter [5].

High impact information on Fmn1

• Formin is a processive motor that requires profilin to accelerate actin assembly and associated ATP hydrolysis [6].
• The association of these transcripts with the gene responsible for the mutant phenotype was established by demonstrating that they are disrupted in two independently arising ld alleles [7].
• In two of these, the ldHd allele (created by insertion of a transgene) and the ldIn2 allele (created by a translocation-inversion involving mouse chromosomes 2 and 17), a common subset of ld transcripts is abolished, but others are apparently unaltered [8].
• As a result of transgene insertion, we previously identified a mutation at the mouse limb deformity (ld) locus that disrupts embryonic pattern formation, resulting in a reduction and fusion of the distal bones and digits of all limbs as well as variable incidence of renal aplasia [7].
• The recent identification of a gene residing at the mouse limb deformity (ld) locus permits us to test the hypothesis that disruption of this gene is responsible for an inherited anomaly affecting embryonic pattern formation [8].

Biological context of Fmn1

• Similarly, activation of the 5' members of the HoxD gene cluster (Hoxd-11 to Hoxd-13) is not affected in ld mutant posterior limb bud mesenchyme, but the subsequent anteriorization of 5' HoxD domains is delayed by about 12 hours and is associated with reduced levels of polarising activity [9].
• In contrast, the deletion of the corresponding genomic region reproduces the ld limb phenotype and is allelic to mutations in Gremlin [10].
• In contrast, our studies establish that the two other ld alleles directly disrupt the neighboring Gremlin gene, corroborating the requirement of this BMP antagonist for limb morphogenesis [10].
• Further doubts concerning an involvement of Formin in the ld limb phenotype are cast, as a targeted mutation removing the C-terminal Formin domain by frame shift does not affect embryogenesis [10].
• Finally, disruption of the epithelial-mesenchymal interactions controlling induction of metanephric kidneys in ld mutant embryos indicates that formin might function more generally in transduction of morphogenetic signals during embryonic pattern formation [11].

Anatomical context of Fmn1

• These results suggest that the ld mesenchyme is unable to induce the formation of a completely functional ridge [12].
• We propose that incomplete differentiation of the AER in ld limb buds leads to reduction of polarizing activity and defects along the anteroposterior axis [13].
• Another common feature among formin family members is their requirement in morphogenetic processes such as budding and conjugation of yeast, establishment of Drosophila oocyte polarity and vertebrate limb pattern formation [11].
• Consistent with these observations, molecular analysis of the limb promordia shows that the limb ectoderm contains a level of ld transcripts fivefold higher relative to its mesenchyme [14].
• Furthermore, expression of ld transcripts in other parts of the developing embryo and in primitive streak embryos (gestational day 7) suggests possible roles for this gene in the earliest determinative events of morphogenesis [14].

Associations of Fmn1 with chemical compounds

• In so doing, we show that a formin isoform (i) is modified by posttranslational phosphorylation at serine and threonine residues and (ii) when present in a crude nuclear extract, is retained by DNA-cellulose [15].
• Specific binding is mediated by the proline-rich domain present in Ld proteins and the ligand binding surface of the Src SH3 domain [16].
• However, bulk and cloned alloreactive CTL that were generated against the mutant Kb glycoprotein Kbm8 reacted strongly with Kb alpha Ld beta [17].
• Lysophosphatidic acid (LPA) stimulates Rho GTPase and its effector, the formin mDia, to capture and stabilize microtubules in fibroblasts [18].
• However, constitutively active mutants of another Rho target, the formin homology protein mDia1 (Watanabe, N., T. Kato, A. Fujita, T. Ishizaki, and S. Narumiya. 1999. Nat. Cell Biol. 1:136-143), were sufficient to restore force-induced focal contact formation in C3 transferase-treated cells [19].

Physical interactions of Fmn1

• A subclass of formins, the Diaphanous-related formins (Drfs), can act as effectors for Rho small GTPases, yet it is not clear what GTPase binding contributes to formin function [20].

Regulatory relationships of Fmn1

• Formin isoforms are differentially expressed in the mouse embryo and are required for normal expression of fgf-4 and shh in the limb bud [13].
• Src regulates the activity of the mammalian formin protein FHOD1 [21].

Other interactions of Fmn1

• However, Shh expression can be rescued by heterospecific grafting of ld mutant posterior mesenchyme under a wild-type chicken AER [9].
• Since ld limbs form distal structures such as digits, we further conclude that while fgf-4 is capable of supporting distal limb outgrowth in manipulated limbs, it is not essential for distal outgrowth in normal limb development [13].
• The present study shows that establishment and positioning of the polarising region is regulated both by restriction of Shh through Gli3 and its positive feedback regulation through formin [22].
• In addition, ld limbs show a severe decrease in the expression of several mesodermal markers, including sonic hedgehog (shh), a marker for the polarizing region and Hoxd-12, a marker for posterior mesoderm [13].
• We describe two mouse Daam cDNAs, mDaam1 and mDaam2, which encode proteins characterized by highly conserved formin homology domains and which are expressed in complementary patterns during mouse development [23].

Analytical, diagnostic and therapeutic context of Fmn1

• Co-immunoprecipitation of Ld and c-Src proteins from transfected cells shows that these proteins associate in vivo [16].
• Whole mount in situ hybridization demonstrated that this targeted disruption was specific for isoform IV and did not interfere with the expression of other ld isoforms [24].
• MATERIALS AND METHODS: RT-PCR and ribonuclease protection analyses were done to characterize the circular RNA transcripts arising from the Fmn gene [25].
• Sequence analysis of formin isoform IV in other ld mutant alleles did not detect any amino acid changes relative to the strain of origin of the mutant allele [24].
• Recovery of the first transgene insertional allele, ldTgHd, facilitated the molecular cloning of a large (greater than 200 kb) candidate gene at the ld locus [26].

References