Gene expression analysis of mammary tissue during fetal bud formation and growth in two pig breeds – indications of prenatal initiation of postnatal phenotypic differences

Kunsuda Chomwisarutkun,Klaus Wimmers,Eduard Murani,Siriluck Ponsuksili

doi:10.1186/1471-213x-12-13

Kunsuda Chomwisarutkun, Klaus Wimmers + Show 2 more

Open Access

https://doi.org/10.1186/1471-213x-12-13

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Abstract

BackgroundThe mammary gland is key to all mammal species; in particular in multiparous species like pigs the number and the shape of functional mammary gland complexes are major determinants of fitness. Accordingly, we aimed to catalog the genes relevant to mammogenesis in pigs. Moreover, we aimed to address the hypothesis that the extent and timing of proliferation, differentiation, and maturation proccesses during prenatal development contribute to postnatal numerical, morphological and functional properties of the mammary gland. Thus we focused on differentially expressed genes and networks relevant to mammary complex development in two breeds that are subject to different selection pressure on number, shape and function of teats and show largely different prevalence of non-functional inverted teats. The expression patterns of fetal mammary complexes obtained at 63 and 91 days post conception (dpc) from German Landrace (GL) and Pietrain (PI) were analyzed by Affymetrix GeneChip Porcine Genome Arrays.ResultsThe expression of 11,731 probe sets was analysed between the two stages within and among breeds. The analysis showed the largest distinction of samples of the breed GL at 63 dpc from all other samples. According to Ingenuity Pathways Analysis transcripts with abundance at the four comparisons made (GL63-GL91, PI63-PI93, GL63-PI63 and GL91-PI91) were predominantly assigned to biofunctions relevant to `cell maintenance, proliferation, differentiation and replacement´, `organismal, organ and tissue development´ and `genetic information and nucleic acid processing´. Moreover, these transcripts almost exclusively belong to canonical pathways related to signaling rather than metabolic pathways. The accumulation of transcripts that are up-regulated in GL compared to PI indicate a higher proliferating activity in GL, whereas processes related to differentiation, maturation and maintenance of cells are more prominent in PI. Differential expression was validated by quantitative RT-PCR of five genes (GAB1, MAPK9, PIK3C2B, PIK3C3 and PRKCH) that are involved in several relevant signaling pathways.ConclusionsThe results indicate that mammary complex development in PI precedes GL. The differential expression between the two breeds at fetal stages likely reflects the prenatal initiation of postnatal phenotypes concerning the number and shape as well as functionality of teats.

Highlights

The mammary gland is key to all mammal species; in particular in multiparous species like pigs the number and the shape of functional mammary gland complexes are major determinants of fitness
Gene expression In order to identify differential gene expression in mammary gland development depending on stage (63 dpc and 91 dpc) and breed (GL and PI) probe sets with present calls in at least 50% of the samples were selected for statistical analysis summing up to 11,731 probe sets
The study provides a holistic view on the gene expression during prenatal development addressing the abundance of 11,731 probe sets at two fetal stages at the phase of growth and protrusion of mammary buds in two pig breeds

Summary

Introduction

The mammary gland is key to all mammal species; in particular in multiparous species like pigs the number and the shape of functional mammary gland complexes are major determinants of fitness. We focused on differentially expressed genes and networks relevant to mammary complex development in two breeds that are subject to different selection pressure on number, shape and function of teats and show largely different prevalence of non-functional inverted teats. In between E28 and E40, the placodes develop into bulbshaped buds of epithelial cells by invagination into the underlying mesenchyme. Late in prenatal development the epithelial buds elongate to the mammary mesenchyme to form a sprout, which creates a small duct. It starts to the ductal elongation and side branching about 10–15 times to form a rudimentary ductal tree. The mammary glands remain at this rudimentary stage, while the epithelial duct slowly grows until it reaches puberty [1,2,3,4,5]

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