Transcriptome profiling of granulosa cells from bovine ovarian follicles during atresia.
BACKGROUND
The major function of the ovary is to produce oocytes for fertilisation. Oocytes mature in follicles surrounded by nurturing granulosa cells and all are enclosed by a basal lamina. During growth, granulosa cells replicate and a large fluid-filled cavity (the antrum) develops in the centre. Only follicles that have enlarged to over 10 mm can ovulate in cows. In mammals, the number of primordial follicles far exceeds the numbers that ever ovulate and atresia or regression of follicles is a mechanism to regulate the number of oocytes ovulated and to contribute to the timing of ovulation. To better understand the molecular basis of follicular atresia, we undertook transcriptome profiling of granulosa cells from healthy (n = 10) and atretic (n = 5) bovine follicles at early antral stages (< 5 mm).


RESULTS
Principal Component Analysis (PCA) and hierarchical classification of the signal intensity plots for the arrays showed primary clustering into two groups, healthy and atretic. These analyses and size-frequency plots of coefficients of variation of signal intensities revealed that the healthy follicles were more heterogeneous. Examining the differentially-expressed genes the most significantly affected functions in atretic follicles were cell death, organ development, tissue development and embryonic development. The overall processes influenced by transcription factor gene TP53 were predicted to be activated, whereas those of MYC were inhibited on the basis of known interactions with the genes in our dataset. The top ranked canonical pathway contained signalling molecules common to various inflammatory/fibrotic pathways such as the transforming growth factor-β and tumour necrosis factor-α pathways. The two most significant networks also reflect this pattern of tissue remodelling/fibrosis gene expression. These networks also contain molecules which are present in the canonical pathways of hepatic fibrosis/hepatic stellate cell activation and transforming growth factor-β signalling and were up regulated.


CONCLUSIONS
Small healthy antral follicles, which have a number of growth outcomes, exhibit greater variability in gene expression, particularly in genes associated with cell division and other growth-related functions. Atresia, on the other hand, not only involves cell death but clearly is an active process similar to wound healing.
Nicholas
N
Hatzirodos
Katja
K
Hummitzsch
Helen F
HF
Irving-Rodgers
Margaret L
ML
Harland
Stephanie E
SE
Morris
Research Centre for Reproductive Health, Discipline of Obstetrics and Gynaecology, School of Paediatrics and Reproductive Health, Robinson Institute, University of Adelaide, Adelaide 5005SA, Australia. ray.rodgers@adelaide.edu.au.
Raymond J
RJ
Rodgers
D000818:Animals; D017209:Apoptosis; D002417:Cattle; D016000:Cluster Analysis; D005260:Female; D005496:Follicular Atresia / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006107:Granulosa Cells / Q000166:cytology / Q000378:metabolism*; D006080:Ovarian Follicle / Q000254:growth & development / Q000378:metabolism*; D010641:Phenotype; D025341:Principal Component Analysis; D015398:Signal Transduction / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53