Genetic and molecular characterization of Drosophila melanogaster mutants with compromised motor and reproductive functions

Abstract

Insects are among the most successful organisms, a success attributed to the evolution of flight and high reproductive capacity. Both locomotion and reproduction are regulated at multiple levels of tissue organization, with neuronal and muscular systems directly controlling these functions. However, the mechanisms of cross-talk between muscles and neurons that regulate locomotor and reproductive systems remain poorly understood. In particular, how genetic alterations in either muscles or neurons give rise to abnormal behaviors is not yet fully clear.

Understanding such interactions is important because both locomotor efficiency and reproductive efficiency are under direct selection pressure. Identifying novel regulators of these functions may provide insights into molecules under selection during insect evolution. This thesis attempts to address these aspects in Drosophila melanogaster using forward and reverse genetic approaches.

Chapter Summaries Chapter 1 - Introduction

Reviews current knowledge on regulation of locomotor and reproductive functions in insects.

Highlights the need for deeper understanding of these processes.

Chapter 2 - Experimental Procedures

Details the methodologies employed in the study.

Chapter 3 - Forward Genetics Study on jumper

Describes a spontaneous flightless mutant, jumper, with open-wing phenotype.

Behavioral analyses revealed reduced flight ability and endurance.

Muscle structural analysis showed no abnormalities, indicating muscle-independent function of the affected gene.

Deletion mapping localized the mutant locus to taxi, a gene encoding a basic helix-loop-helix protein expressed in muscle attachment cells.

Molecular sequencing revealed insertion of a truncated sequence of an “I-element” retrotransposon in the 5 UTR of taxi.

Complementation studies confirmed the hypomorphic nature of the jumper allele.

Tissue-specific knockdown of taxi demonstrated its essential role in neurons and muscle attachment cells for proper wing posture and flight ability.

Chapter 4 - Reverse Genetics Study on Beadex (Bx)

Bx encodes a LIM-only domain-containing protein.

Loss-of-function alleles of Bx resulted in flightlessness and reduced walking ability.

Mutant females showed reduced fecundity and fertility, attributed to impaired ovulation and sperm release from storage organs.

Neuronal knockdown of Bx phenocopied reproductive defects, highlighting its role in neurons for female reproductive ability.

Motor neuron-specific knockdown was sufficient to reduce female reproductive functions.

Chapter 5 - Role of Bx in Ovaries

Revealed specific requirement of Bx in somatic cells, rather than germ cells, of the ovary for female reproduction.

Chapter 6 - Molecular Pathways of Bx

Whole-genome expression profiling of mutant Bx brains identified differential regulation of genes involved in synaptic development and function.

Suggested compromised neuromuscular signaling as a mechanism underlying mutant phenotypes.