bio lecture 03/04

Introduction

• Focus on patterning and body axes in multicellular organisms, specifically in bilateral symmetrical animals.

• Understanding body orientation:

  • Anterior: head end

  • Posterior: tail region

  • Left and Right: lateral orientation

  • Ventral: stomach side

  • Dorsal: back side

• These axes are established during embryonic development.

Model Organism: Drosophila

• Drosophila (fruit flies) as a model organism for biological research due to:

  • Their rapid generation time.

  • High number of offspring.

  • Genetic similarities to humans.

  • Approximately 70% of genes related to human disease are conserved.

• Considerations before choosing Drosophila as a model for studying human diseases:

  • Are the genes involved in the disease present in Drosophila?

  • Are the developmental processes similar in Drosophila?

  • Can we easily create mutants for study purposes?

Anterior-Posterior Axis Development

• Emphasis on anterior-posterior orientation in Drosophila development.

• Structure of Drosophila discussed:

  • Head (anterior)

  • Thoracic segments (middle)

  • Abdominal segments (posterior)

• Factors influencing gene expression patterns in specific cells:

  • Transcription factors activating gene expression.

  • Intercellular signaling to determine body part development.

Experimental Approaches to Study Gene Involvement

Find It Experiment

• Fluorescence In Situ Hybridization (FISH) used to visualize bicoid mRNA in embryos.

• Anticipated results if bicoid coordinates anterior development:

  • Expect fluorescence at the anterior end, indicating gene expression.

  • Observations confirm bicoid mRNA localized at the anterior edge of the embryo.

• Important distinction: mRNA presence indicates gene expression, not just DNA presence.

Lose It Experiment

• Analyzing bicoid-deficient mutants to observe developmental consequences:

  • Wild-type flies show normal anterior structures.

  • In bicoid mutants, anterior structures absent, replaced by posterior structures.

  • Bicoid's role: essential for anterior structure setting; its loss results in a 'two-tailed' phenotype, prompting the name 'bicoid' (meaning 'two tails').

Factors Influencing Protein-DNA Binding

• Affinity: likelihood of protein binding to DNA based on structure and charge.

• Concentration: the amount of protein available influences binding probability.

• Understanding the importance of both affinity and concentration in protein binding dynamics throughout the embryo development.

Syncytial Blastoderm Stage

• Conceptual architecture of the early Drosophila embryo:

  • Defined as a syncytial blastoderm, where nuclei replicate without corresponding cellular division.

  • Diffusion of molecules (like proteins) across nuclei is possible in this state.

Understanding Morphogens and Cytoplasmic Determinants

• Bicoid is a cytoplasmic determinant present at the anterior end, influencing development.

• Distinction between a morphogen (substance that dictates cell fate depending on its concentration) and a cytoplasmic determinant (factor inherited from the mother that influences development).

Conclusion

• Key takeaway points:

  • The conservation of genetic elements across species.

  • The role of bicoid in regulating anterior development.

  • The experiments that help determine gene function and expression patterns.

• Review distinctions between morphogens and cytoplasmic determinants for further understanding in laboratory settings.