Building on models to study the evolution of viviparity in Australian skinks

Second, to investigate the evolution of maternal-fetal signalling I used RNASeq data of the uterus and fetal placenta from the viviparous southern grass skink (<i>Pseudemoia entrecasteauxii</i>) and oviparous garden skink (<i>L. guichenoti</i>) and viviparous (<i>P. entrecasteauxii</i>) to show that communication is a potential driver of the evolution of pregnancy-specific gene regulation.. To verify whether spurious signalling occurs, I developed an in vitro system to co-culture the uterine tissue with and without chorioallantoic membrane (CAM) to stimulate the placenta status after the eggshell reduction.

In both oviparous and viviparous skinks, uterine gene expression changes significantly in the presence of the CAM. The differentially expressed genes in oviparous and viviparous tissue cultures are enriched in pathways for cilium and microtubule processing in both species, key processes in the tissue remodeling of placentation. Third, to understand the genomic mechanisms supporting the evolution of a placenta, I assembled and compared high quality genome assemblies of oviparous and viviparous skinks (<i>Pseudemoia entrecasteauxii</i>, <i>Acritoscincus duperreyi</i>, <i>Lampropholis delicata</i>, <i>Lampropholis guichenoti</i>, <i>Carinascincus ocellatus</i>) to explore gene family expansions, using CAFE5.

I identified more than 100 expanded gene families in each species, and viviparous skinks show the different gene family expansion pattern with oviparous skinks. There are 33 expanded gene families shared by viviparous skinks (<i>P. entrecasteauxii</i> and <i>C. ocellatus</i>), and 11 of them are involved in regulation of endopeptidase activity and deoxyribonucleotide biosynthetic process and immune response, which are important metabolic processes during human pregnancy.

Among the pregnancy functional expanded gene families, <i>ADAM20</i>, <i>SOAT2</i>, <i>SLC44A4 </i>and <i>KLHL23 </i>are significantly expressed in viviparous species, and gene family expansion may have allowed one copy of the gene to retain its ancestral function while another copy diverged in expression and potentially acquired placenta-associated roles.. Overall, this thesis combines genomic, transcriptomic, and experimental analyses into a framework for investigating the mechanisms that support the evolution of viviparity and placentation in reptiles, with Australian skinks as a model system.</p>