Variation of Leptin-Melanocortin Signaling Pathway Genes and their Genetic Effects on Body Weight, Linear Body Measurements and Fatness Traits in Sheep

Contents

Chapter 1 Introduction and Literature Review

1.1 Introduction

1.1.1 Problem Statement

1.1.2 Justification

1.2 Candidate gene approach and genetic association

1.3 Genetic markers

1.3.1 Restriction fragment length polymorphisms (RFLPs)

1.3.2 Microsatellites

1.3.3 Single nucleotide polymorphisms

1.4 SNP Discovery Methods

1.5 Use of SNP Markers in Industry

1.6 The sheep growth and development

1.7 Fat deposition and meat value

1.8 The melanocortin system genes

1.9 Central neural circuits energy homeostasis

1.10 A leptin/melanocortin pathway

1.11 MC4R gene polymorphism in livestock

1.12 STAT3 gene polymorphism in livestock

1.13 Overview of Experiments, Hypotheses and Objectives

1.13.1 General Overview

1.13.2 Study One: The leptin-melanocortin system modulates rapid growth and muscular high-yield carcass in sheep through adipocytokine signaling pathway.

1.13. 3 Study Two: Genetic Variations in the MC4R gene linked to elevated body weight and fat-related traits in sheep

1.13.4 Study Three: STAT3 Gene Expression and Its Role in Sheep Body Weight and Fatness Modulation

1.13.5 Study Four: Single Nucleotide Polymorphisms in the Leptin Gene and Their Associations with Growth and Fat-deposition Traits in the sheep

CHAPTER 2 The leptin-melanocortin system modulates rapid growth and muscular high-yield carcass in sheep through adipocytokine signaling pathway.

2.1 Abstract

2.2 Introduction

2.3 Materials and Methods

2.3.1 Function and pathway enrichment analysis

2.3.2 Library preparation and Transcriptome analysis

2.3.3 Single nucleotide polymorphisms (SNPs) detection from re-sequenced data

2.3.4 Analyses of positive selection

2.4 Results

2.4.1 GO function and KEGG pathway enrichment analysis

2.4.2 Polymorphism analysis

2.4.3 Positive selection of the leptin-melanocortin genes by FDIST analysis

2.4.4 Analysis of positive selection

2.4.5 Haplotype structure

2.4.6 The relative transcript abundance of the genes involved in the Leptin-melanocortin signaling pathway

2.5 Discussions

2.6 Conclusion

CHAPTER 3 Genetic Variations in the MC4R gene linked to elevated body weight and fat-related traits in sheep

3.1 Abstract

3.2 Introduction

3.3 Materials and Methods

3.3.1 Ethical statement

3.3.2 Experimental animals and measurements

3.3.3 Blood collection

3.3.4 Isolation of genomic DNA

3.3.5 Evaluation of the quality, purity, and concentration of DNA

3.3.6 Designing of primers

3.3.7 PCR reaction mixture

3.3.8 PCR program

3.3.9 Checking of amplified PCR products

3.3.10 Identification of Single Nucleotide Polymorphisms (SNPs)

3.3.11 RNA Extraction and Real-Time qPCR

3.3.12 Sequence Characterization of the Potential Promoter Region of MC4R in Sheep

3.3.13 Promoter Cloning and Generation of Luciferase Reporter Constructs

3.3.14 Purification of PCR product by PCR Clean-Up System (Omega Bio-Tek, Inc., Norcross, GA, USA)

3.3.15 Vector ligation of amplified products

3.3.16 Competent cell preparation and transformation

3.3.17 Confirmation of positive clones

3.3.18 Colony PCR

3.3.19 Plasmid isolation from positive clones

3.3.20 Plasmid digestion by Restriction Endonuclease enzymes

3.3.21 Cell Culture, Transfection, and Luciferase Assays

3.3.22 Statistical Analysis

3.3.23 Association Analysis

3.3.24 Expression Analysis

3.4 Results

3.4.1 Single Nucleotide Polymorphism (SNP) Identification

3.4.2 SNP Variation in Potential Cis-Regulatory Elements of the MC4R Gene

3.4.3 Association Analyses

3.4.4 Linkage disequilibrium and Haplotype Analysis of the MC4R Gene

3.4.5 Sequence Analysis of the Promoter Region of MC4R Gene

3.4.6 Differential Expression of the MC4R Gene across Age and Sex

3.4.7 The Proximal Minimal Promoter Region of the MC4R Gene

3.5 Discussion

3.6 Conclusions

CHAPTER 4 STAT3 Gene Expression and Its Role in Sheep Body Weight and Fatness Modulation

4.1 Abstract

4.2 Introduction

4.3 Materials and methods

4.3.1 Sample Collection

4.3.2 Lipid extraction-soxhlet method

4.3.3 PCR Amplification, Sequencing, and Genotyping

4.3.4 Sequence analysis

4.3.5 Collection of RNA Samples

4.3.6 RNA Purification and cDNA Synthesis

4.3.7 SYBR Green RT-PCR Analysis of Expression Patterns

4.3.8 Immunohistochemical localization and analysis of STAT3

4.3.9 Statistical analysis

4.4 Results

4.4.1 The sequence of the sheep STAT3 gene

4.4.2 STAT3 relative mRNA Expression in Sheep

4.4.3 Immunohistochemical analysis

4.4.4 SNP Identification and Analysis of Its Association with body size traits

4.4.5 Effect of the polymorphisms on STAT3 locus on body measurement and fat deposition traits

4.4.6 Linkage disequilibrium and haplotype analysis

4.5 Discussion

4.6 Conclusions

CHAPTER 5 Single Nucleotide Polymorphisms in the LEP Gene and Their Associations with Growth and Fat-deposition Traits in the sheep

5.1 Abstract

5.2 Introductions

5.3 Experimental Section

5.3.1 Materials and Phenotypic Data Collection

5.3.2 PCR Amplification and SNP Identification

5.3.3 SNP Identification and Genotyping

5.3.4 Statistical Analysis

5.3.5 Computational analysis of LEP gene

5.4 Results

5.4.1 SNP Identification and Genotyping

5.4.2 Association Analysis with Growth Traits

5.4.3 Data mining

5.4.4 Non-synonymous SNPs functional analysis for LEP

5.4.5 Mutant protein stability prediction for LEP

5.4.6 Structural conformation and conservation analysis by ConSurf sever

5.4.7 LEP protein secondary structure prediction by PSIPRED

5.4.8 Homology Modelling

5.4.9 Ramachandran plot analysis

5.4.10 LEP gene protein-protein interaction

5.5 Discussion

5.6 Conclusion

CHAPTER 6 General Conclusions, innovations and future directions

6.1 Conclusions

6.2 Innovations

6.3 Future directions

Research Objectives and Themes

The primary research objective is to identify and characterize the genetic variations in the leptin-melanocortin signaling pathway—specifically focusing on MC4R, STAT3, and LEP—and to evaluate their association with growth, body measurement, and fat deposition traits in various Chinese sheep breeds to facilitate marker-assisted selection.

• Characterization of genetic variations (SNPs/haplotypes) in target genes (MC4R, STAT3, LEP) across diverse sheep populations.
• Analysis of the association between identified genetic markers and economic production traits like body weight, body measurements, and fat deposition.
• Investigation of the transcriptional regulation of candidate genes, specifically the promoter regions and their functional impact on mRNA expression.
• Evaluation of protein stability and structure through computational (in silico) analyses to predict the functional consequences of missense mutations.
• Assessment of potential utility for marker-assisted selection (MAS) and genomic improvement programs in the sheep breeding industry.

Excerpt from the Book

Summary of Chapters

Chapter 1 Introduction and Literature Review: Provides a foundational overview of animal breeding methods, the mechanism of the leptin-melanocortin pathway, and the relevance of molecular markers in sheep production.

CHAPTER 2 The leptin-melanocortin system modulates rapid growth and muscular high-yield carcass in sheep through adipocytokine signaling pathway.: Screens 14 target genes within the pathway to identify those under positive selection and their potential role in growth and carcass traits using transcriptome and bioinformatics analysis.

CHAPTER 3 Genetic Variations in the MC4R gene linked to elevated body weight and fat-related traits in sheep: Details the identification of SNPs within the coding and promoter regions of the MC4R gene, characterizing its promoter, and analyzing their associations with various body measurement traits.

CHAPTER 4 STAT3 Gene Expression and Its Role in Sheep Body Weight and Fatness Modulation: Investigates the STAT3 gene's sequence, tissue-specific expression patterns, and the statistical association between identified mutations and phenotypic traits in sheep.

CHAPTER 5 Single Nucleotide Polymorphisms in the LEP Gene and Their Associations with Growth and Fat-deposition Traits in the sheep: Explores genetic variations in the LEP gene, their functional impacts on protein stability via computational prediction tools, and their correlation with growth and fat deposition performance.

CHAPTER 6 General Conclusions, innovations and future directions: Synthesizes findings across studies to highlight the potential for multi-gene assisted selection and future research trajectories in improving sheep meat production.

Keywords

Body weight, Fat deposition traits, Genetic selection, In silico, Leptin (LEP), Melanocortin 4 receptor (MC4R), Regulatory variants, Sheep, Signal transducer and activator of transcription 3 (STAT3), Single nucleotide polymorphisms, Marker-assisted selection, Growth traits, Transcriptome analysis, Promoter region.

Frequently Asked Questions

What is the core focus of this PhD dissertation?

This thesis investigates the genetic basis of growth, body measurement, and fat deposition traits in Chinese meat-type sheep breeds by analyzing variations in key genes of the leptin-melanocortin signaling pathway.

Which specific genes are analyzed in this research?

The work primarily focuses on the Melanocortin 4 receptor (MC4R), Signal transducer and activator of transcription 3 (STAT3), and Leptin (LEP) genes, identifying how their variations influence sheep productivity.

What is the primary objective of these studies?

The primary goal is to characterize the genetic effects of these pathway genes and validate them as potential genetic markers for marker-assisted selection (MAS) to improve sheep meat yield and composition.

What scientific methods were employed?

The researchers used a combination of PCR-direct sequencing, bioinformatics functional genomics, transcriptome expression profiling (RNA-seq), immunohistochemistry (IHC), and promoter/luciferase reporter assays to examine gene function and regulation.

What does the main body of the work cover?

The body chapters detail individual experiments on specific genes (MC4R, STAT3, LEP), covering SNP discovery, association analyses with physiological traits, and biological/functional validation of these variations.

How are the key results defined by specific keywords?

Key results are categorized by terms such as "Marker-assisted selection," "Single nucleotide polymorphisms," "Cis-regulatory elements," and "Body measurement traits," which underscore the study's practical application in breeding.

Why are the promoter variants of the MC4R gene considered significant?

The identification and characterization of the MC4R promoter variants are crucial because they directly affect gene expression and transcriptional regulation, potentially offering highly effective markers for selecting sheep with superior body size.

How does the research address the functional impact of nsSNPs in the LEP gene?

The research uses advanced in silico (computational) analysis tools—such as SIFT, PredictSNP2, PROVEAN, and SNAP2—to predict the damaging or neutral effects of non-synonymous single nucleotide polymorphisms (nsSNPs) on protein structure, stability, and function.

What is the significance of the H1H2 diplotype in sheep?

The study found that the H1H2 diplotype in the MC4R gene is significantly associated with heavier body weight, making it a valuable target for future breeding selection to increase animal productivity.