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#gene function

16 public questions tagged with this topic.

Elegans -ll

What is the function of MOM-2 in C. elegans?

MOM-2 encodes C. elegans Wnt homolog expressed in P2 blastomere at 4-cell stage. It binds MOM-5 Frizzled receptor on EMS, collaborating with MES-1/SRC-1 pathway to activate WRM-1 beta-catenin and MAPK signaling, resulting in phosphorylation and downregulation of POP-1 TCF in posterior daughter E. Converted POP-1 together with higher SYS-1 beta-catenin activates transcription of end-1, end-3 endoderm determinants. mom-2 mutants phenocopy loss of P2 signal, causing both EMS daughters to become MS-like. Thus primary function of MOM-2 is to activate Wnt signaling establishing EMS polarity and endoderm specification.

Ref: Thorpe et al. 1997; Gilbert Chapter 4: MOM-2 function - activates Wnt signaling in EMS specification.

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Elegans -ll

What happens in embryos lacking functional LAG-2?

LAG-2 encodes Delta-like ligand for LIN-12 and GLP-1 Notch receptors. In early embryo, ABa and MS express GLP-1 while P2 presents LAG-2 and APX-1 to activate GLP-1 in ABp for A-P patterning of pharynx. In gonad, Z1.ppp/Z4.aaa require LAG-2/LIN-12 interaction to decide anchor cell versus ventral uterine fate. Without functional LAG-2, GLP-1 and LIN-12 receptors remain unbound, NICD cleavage fails, downstream targets lag-1 dependent transcription silent. Consequently ABp to ABa transformation and AC/VU defects occur, but fundamentally LIN-12 remains inactive due to absent ligand triggering, revealing ligand-dependent activation mode of Notch signaling in nematode.

Ref: Henderson et al. 1994; Gilbert Chapter 4: LAG-2 loss - LIN-12 remains inactive due to ligand absence.

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Elegans -ll

Which gene is required for primary vulval precursor cell fate?

LIN-39, C. elegans HOX5 ortholog, specifies vulval precursor cell competence and primary fate potential. It is expressed in central body region P3.p-P8.p during L1-L2, preventing fusion with hypodermal syncytium and promoting vulval competence by activating egl-17 and repressing fusion genes eff-1. Without LIN-39, all VPCs fuse prior to anchor cell signaling, yielding vulvaless phenotype even if LIN-3 present. LIN-39 also cooperates with Ras-MAPK to drive primary fate in P6.p by enhancing lin-3 responsiveness. LIN-12 Notch instead promotes secondary fate, and SKN-1 is embryonic factor, making LIN-39 central to VPC competence.

Ref: Clark et al. 1993; Gilbert Chapter 15: LIN-39 required for primary vulval precursor cell fate competence.

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Elegans -ll

Which of the following statements correctly describes SKN-1 function?

SKN-1, maternally provided bZIP transcription factor related to Nrf, accumulates in P1 and later EMS blastomere due to PAR polarity and SKR-mediated regulation. It directly binds promoters of med-1, med-2 GATA factors, initiating mesendoderm program that subsequently activates end-1, end-3 and tbx-35 for E versus MS divergence. skn-1 mutants lack pharynx and intestine derived from EMS, with EMS transforming to C-like muscle fate. It does not regulate LIN-39 or vulval signaling, but serves as earliest zygotic activator connecting maternal polarity to zygotic endomesoderm specification, upstream of Wnt-modified POP-1 decision mechanism.

Ref: Bowerman et al. 1992; Gilbert Chapter 4: SKN-1 regulation of EMS fate via MED factors.

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Limb Development -ll

Which of the following describes the function of PITX1 in limb development?

PITX1 is a paired-type homeodomain transcription factor restricted to hindlimb mesenchyme, serving as master hindlimb identity regulator throughout development. It directly activates TBX4 expression and represses forelimb genes, controlling hindlimb-specific characteristics including elongated femur shape, patella formation, tendon pattern and Pitx1-dependent hindlimb muscle via Tbx4-FGF10 axis and Hox genes. Transgenic loss or Pitx1 mutant mice show partial forelimb-like transformation of hindlimbs, altered knee articulation and clubfoot phenotypes. It does not maintain FGF8 directly, inhibit forelimb growth globally, or block Wnt signaling. Its role is activating hindlimb-specific program.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: PITX1 activates hindlimb-specific gene program.

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Drosophila -ll

Mutant lacking dorsal gene becomes:

Dorsal protein, NF-kappa B homolog, provides ventralizing morphogen; its absence eliminates ventral and lateral fates causing entire embryo to adopt dorsal ectoderm identity characterized by amnioserosa and dorsal hairs circumferentially. Embryos lacking dorsal fail to form ventral furrow, mesoderm, or neuroectoderm, cuticle shows dorsalized phenotype with fine hairs everywhere, lethal before hatching. Ventralized phenotype arises from opposite genotype such as cactus loss or Toll gain. Anteriorized or posteriorized phenotypes involve bicoid or torso pathways. Dorsal loss therefore demonstrates necessity of NF-kappa B-like gradient for DV patterning, innate immunity cross-regulation, providing model linking developmental polarity and inflammatory signaling pathway conservation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: dorsal null mutants become dorsalized - loss of ventral nuclear gradient.

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plant Development -ll

GURKE (GK) gene encodes:

GURKE, synonymous with PASTICCINO3 and EMB22, encodes ACC1 cytosolic homomeric acetyl-CoA carboxylase catalyzing ATP-dependent carboxylation of acetyl-CoA to malonyl-CoA precursor for very-long-chain fatty acids, sphingolipids, cuticular waxes, and seed triacylglycerols. VLCFA-derived lipid signals modulate cytokinin and auxin homeostasis in globular embryo apex. gurke mutants fail to partition apical dome into three subdomains: two cotyledon anlagen, central WUS-expressing shoot organizing center, and CUC-expressing boundary regions. Seedlings display fused cotyledons and disrupted meristems, directly linking lipid metabolism to developmental fate patterning and meristem organization.

Ref: Baud et al., Plant J 2004; Kajiwara et al., Plant Cell Physiol 2004: GURKE encodes acetyl-CoA carboxylase ACC1 for embryo partitioning.

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plant Development -ll

GNOM gene encodes:

Arabidopsis GNOM, also known as EMB30 or VAN7, encodes brefeldin A-sensitive ARF-GEF, guanine nucleotide exchange factor for ADP-ribosylation factor small GTPases. It localizes to recycling endosomes and trans-Golgi network regulating vesicle budding required for polar cargo delivery. Principal cargo includes PIN1 and related PIN auxin efflux carriers whose polar plasma membrane localization depends on GNOM-mediated endosomal recycling. Disruption impairs directional auxin transport causing embryonic and post-embryonic defects resembling auxin transport inhibitor treatments, revealing link between membrane trafficking machinery and hormonal patterning controlling embryogenesis and lateral root development.

Ref: Geldner et al., Cell 2003; NCBI Bookshelf, Plant ARF-GEF: GNOM encodes BFA-sensitive ARF-GEF regulating PIN recycling.

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Gene Dissection and Complementation

Overall, gene dissection and complementation help in understanding

Gene dissection and complementation methods reveal how numerous nuclear genes cooperate to build traits through linear biochemical pathways and regulatory networks. Although dataset lists options concerning mitochondrial mutation imprinting and chromosome loss, deletion mapping and somatic hybrid panels use similar logic to correlate absence of chromosome segment with loss of multiple complementation groups simultaneously. Observing loss of phenotype when chromosome missing indicates genes reside there, so chromosome loss phenotype reflects elimination of many functions simultaneously, extending complementation concept to cytogenetic scale of physical mapping and aneuploidy analysis.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 12: Chromosome Loss Deletions and Functional Mapping Techniques

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Gene Dissection and Complementation

Genetic dissection experiments assume enzymes act

Genetic dissection models metabolism as ordered conversion chain where product of one enzymatic reaction becomes substrate for next ensuring directional flux toward final functional product. Enzymes act not randomly but in defined sequence establishing epistasis and accumulation patterns diagnostic for pathway order. B enzyme produces compound used by C enzyme so knockout of early enzyme prevents downstream synthesis of later intermediates. This sequential logic allows prediction of intermediate build-up and rescue patterns enabling mapping of steps to specific cistrons and understanding why upstream blocks have broader nutritional requirements than downstream blocks.

Ref: Snustad & Simmons, Principles of Genetics, 7th ed., Chapter 14: Sequential Enzyme Model for Pathway Dissection

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Gene Dissection and Complementation

If six mutants fall into three complementation groups, it indicates

Evaluating six mutants producing three complementation groups involves pairwise trans tests clustering non-complementing mutants together into shared groups. Each group contains mutants allelic to each other but complementing members of other groups indicating distinct functional units. Number of groups equals number of genes whose inactivation yields same phenotype because each group corresponds to one cistron encoding one enzyme or structural component. Therefore six isolates falling into three groups reveal three distinct genes required for pathway not six independent loci, simplifying genetic architecture and indicating limited gene set.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 7: Gene Number from Complementation Groups Calculation

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Gene Dissection and Complementation

Complementation analysis cannot be used for

Complementation test depends on ability of wild-type allele to mask recessive defect by providing functional product in heterozygote. Dominant mutations express phenotype even with single copy so trans configuration containing dominant allele plus wild homologue still shows mutant trait regardless of second mutation location preventing discrimination between allelic and non-allelic lesions. Dominance masks capacity for complementation causing universal failure pattern and uninterpretable results. Therefore test restricted to recessive loss-of-function alleles where wild allele can supply normal function if separate locus, excluding dominant traits from functional analysis applicability.

Ref: Pierce, Genetics: A Conceptual Approach, 7th ed., Chapter 8: Dominant Mutations Limit Complementations Interpretation

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