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Significant advances have been made in the morphological observations of the dorsal gland (DG), an oval organ/tissue which lies on both sides of the dorsal midline of the crocodilian. In the current study, RNA sequencing (RNA-seq) was used to identify the changing patterns of Alligator sinesis DGs at different timepoints from the 31st embryonic day (E31) to the newly hatched 1st day (NH1). A comprehensive transcriptional changes of differentially expression gene (DEGs) involved in the melanogenesis, cholesterol metabolism, and cell apoptosis pathways suggested that the DG might serves as a functional secretory gland in formation, transport and deposition of pigment, and lipids secretion via lysosomal exocytosis. Furthermore, the remarkable immunohistochemical staining of proliferating cell nuclear antigen (PCNA) and B-cell lymphoma 2 (Bcl-2)-positive signals in the basilar cells, in parallel with the immuno-reactive TdT-mediated dUTP nick-End labeling(TUNEL) within suprabasal cells, provided direct molecular evidence supporting for the speculation that DG serves as a holocrine secretion mode. Finally, subsequent phylogenetic and immunohistochemical analysis for the PITX2, the identified DEGs in the RNA-seq, was helpful to further elucidate the transcriptional regulatory mechanism of candidate genes. In conclusion, the current results are of considerable importance in enriching our understanding of the intrinsic relationship between the skin derivatives and lifestyles of newborn Alligator sinesis.

Habitat loss and degradation are among the leading causes of local extinctions, so it is crucially important to preserve and restore the remaining critical habitat increasingly critical to conserve biodiversity. However, mechanisms driving species extinction often begin with habitat loss and seldom are well understood, which is greatly limits our ability to mitigate their impacts. The Chinese Alligator (Alligator sinensis) is a critically endangered crocodilian, which is narrowly distributed in very small six regions of Anhui province, China. In the present study, we used 9 nuclear microsatellite loci genotyped across the taxon's distribution area to investigate genetic variation and population demography in A. sinensis. The Chinese Alligator showed unusually low levels of genetic diversity (Na, 5.44; Ne, 1.97; He, 0.47) based on 793 individuals. Msvar analyses found recent signals of population decline reflecting a bottleneck (an approximately 9-fold decrease) about 25,000 years ago. Ecological niche modelling indicated that the habitat area has declined (about 8–15 fold) for A. sinensis when compared with that under different historical climatic conditions. Our results indicated that population decline and habitat loss in critically endangered Chinese Alligators may have acted as intrinsic and extrinsic factors that have impacted the current status of A. sinensis. In addition, these two unfavorable factors may have also directly contributed to a reduction in the genetic diversity of A. sinensis. Keywords: Alligator sinensis, Genetic diversity, Population demography, Niche reconstruction