A review of the Potential Genes Implicated in Follicular Atresia in Teleost Fish

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Molecular approach to study of atresia

The study of molecular mechanisms involved in atresia has begun to be studied from a perspective that allows to determine genes regulating this process (Nicol et al., 2013, Miranda et al., 2013). Studies in transcriptomics have provided valuable information about the molecular events that lead to ovulation (Babin et al., 2007; Tingaud-Sequeira et al., 2009, Martyniuk et al., 2013), and for many species the transcriptional response can be associated with physiological changes and morphological events that are occurring in the ovary (Gardner et al 2012, Martyniuk et al., 2013). Ovaries can provide transcriptomic specific maturation profile in mature individuals, which can be associated with specific biological processes for each stage of oocyte development, which would allow understanding the dynamics of the process of atresia in natural populations (Villeneuve et al., 2010; Lubzens et al., 2010; Martyniuk et al., 2013).
For some species (The Atlantic bluefin Thunnus thynnus, sole Solea senegalensis, Japanese medaka Oryzias latipes and black bass Micropterus salmoides) it has been determined candidate genes that would have a putative role in the process of atresia. Of the described, the Fst gene encoding the protein follistatin (FST) is probably a marker of ovarian age (Herpin et al., 2013), genes associated with lipid trafficking, such as the genes of the FABP superfamily (Fabp1, Fabp4 and Fabp11) (Agulleiro et al., 2007, Gardner et al., 2012). For Micropterus salmoides expression profiles for atresia are quite different to other oocyte development stages, being genes related to oxidative metabolism higher in atretic but lower the genes that participate in gap junction pathways of the cytoskeleton, among others (Martyniuk et al., 2013).

Biological Model: Chilean Jack mackerel, Trachurus murphyi Nichols 1920

The pelagic Chilean jack mackerel Trachurus murphyi Nichols1920 (Figure 12) is one the most important fishing resource in the South-eastern Pacific Ocean. Due at the overexploitation favoured by the oversizing of all the industrial fleet, they ended up triggering the biggest fishing crisis of the decade for this fishing resource. For population of T. murphyi in Chile, the reduction was 44% of the biomasa, landing of ca. 4.600.000 tons by 1996 drop dramatically to less than 300.00 tons by 2017 (Figure 13); generating critical changes in the age structure of the populations and all sustainability of the fishery of this resource (Figures 13) (Arcos et al., 2004; SPRFMO 2018).

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Hypothesis

– Due the extended distribution of the spawning area of T. murphyi, Prevalence and intensity of atresia in Trachurus murphyi is expected to show spatial and temporal variability correlated with length, gonadosomatic index and condition factor. Alternatively, variations in atresia will be correlated with extrinsic factors (sea surface temperature, year).
-Species highly migratory like Trachurus murphyi, are exposed to several variables (environmental and physiology) that can produce that females delay or fail the reproduction, then is expected a differential transcriptomic expression between females showing atresia and not atresia.
– The presence of parasites can be generated change in phisiologycal responce in host, including reproductive process, then is expected that females showing protozoan parasites Goussia cruciata will have more atretic oocytes than females without this parasite.

Table of contents :

ACKNOWLEDGMENTS
LIST OF TABLES
LIST OF FIGURES
1.- GENERAL INTRODUCTION 
1.1.- Fisheries and fish reproduction
1.2.- Maturation and reproductive success
1.3.- Reproductive cycle of female
1.4. Oogenesis
1.5.- Follicular atresia
1.6.- Parasites affect reproduction
1.7. Molecular approach to study of atresia
1.8.- Biological Model: Chilean Jack mackerel, Trachurus murphyi
2. CONTEXT OF THE THESIS 
3. HYPOTHESIS 
4. OBJETIVES 
5. RESULT 
5.1 CHAPTER 1  A review of the Potential Genes Implicated in Follicular Atresia in Teleost Fish
5.2 CHAPTER 2  Atresia in the Chilean jack mackerel Trachurus murphyi (Teleostei, Carangidae): A first assessment for the South-eastern Pacific Ocean.
5.3 CHAPTER 3  First transcriptomic approach to the study of atresia in Trachurus murphyi using RNA-Seq analysis: genes associated with the follicular atresia.
5.4 CHAPTER 4  The first report of liver coccidian Goussia cruciata in jack mackerel Trachurus murphyi from the South Pacific and its relationship with host variables.
6.- GENERAL DISCUSSION AND CONCLUSIONS 
6.1 General discussion
6.2 Conclusions
7. FORTHCOMING 
8. REFERENCES 
RESUMEN
RÉSUMÉ – ABSTRACT

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