Follicular Development and Reproductive Characteristics in Four Species of Brazilian Tropidurus Lizards

Morphological evidence for the physiological nature of follicular atresia in veiled chameleons (Chamaeleo calyptratus)

Follicular atresia (FA) has been assumed to serve different functions in reptiles, e.g. helping to develop hierarchies, limiting clutch size, and regression of ovarian structures. Reproductive output is dependent on a balance between ovulations and FA. Excessive rates of FA may not only be detrimental for the survival of a population, but have also been associated with pathological conditions. In order to gain insights into the physiological and potentially pathological processes of FA, we performed a decriptive study on the morphological features of the ovaries in sexually mature female veiled chameleons (Chamaeleo calyptratus, VC). Of 60 clinically healthy female VC with continuous ovarian cycling and at least one confirmed cycle with FA over at least 1.5 years, 30 were selected for macroscopic evaluation of ovarian appearance and 7 were subjected to histology and immunohistology. While FA of previtellogenic follicles happened at a low rate, expected for a species with two germinal beds per ovary and polyautochronic reproductive pattern, atresia in the late vitellogenic stage affected entire generations of follicles, consequential to ovulatory failure. Histologically, no pathological processes were identified in any of the animals. Rather, three stages of FA (early, middle, late) were defined and vitellogenic follicles showed two distinct morphological types of FA: yolky and cystic. Yolky FA was found in 21/30 (70%) animals, while cystic FA co-occurred in 9/30 (30%) of the animals.

ULTRASONOGRAPHIC AND COMPUTED TOMOGRAPHIC CHARACTERISTICS OF THE REPRODUCTIVE CYCLE IN FEMALE VEILED CHAMELEONS (CHAMAELEO CALYPTRATUS)

Female veiled chameleons, Chamaeleo calyptratus, have a high fecundity and fast maturation, which makes them a suitable model species for squamate reproduction. The authors investigated the morphological follicular development of a group of 20 healthy adult animals over a 12-mon period using ultrasonography (US) and CT. Four stages of follicular development could be distinguished by imaging diagnostics and were confirmed by histology: previtellogenesis, vitellogenesis, gravidity, and atresia. Using a linear ultrasound transducer (18 MHz), previtellogenic follicles could be visualized as small, round, hypoechoic structures. Identification of this stage was unreliable on CT. On US, vitellogenic follicles remained round and showed increasing echogenicity from the hypoechoic center outwards, displaying vinyl-like hyperechoic banding in later stages. On CT, early vitellogenic follicles were round, hyperdense structures, which reduced in density as they grew. A hyperdense inner ring with a hypodense central point characterized late vitellogenesis. Following ovulation, eggs became distinctly oval on both CT and US, with formation of a hyperdense or hyperechoic outer ring, respectively. Atresia followed in cases where no ovulation occurred, and was divided into yolky and cystic atresia. Sonographically, early yolky atretic follicles became unevenly shaped, packed against one another, and developed heterogenous content. Late atretic follicles were homogenous and reduced in size. Reduction of density and uneven shape were also observed on CT. Cystic atretic follicles developed an anechoic cavity with a dense peripheral accumulation of content. In many animals 2-3 generations of atretic follicles were observed without indication of impairment to the development of the newest batch of follicles. Thus, follicular atresia need not necessarily lead to a pathological condition in veiled chameleons, at least not within a few consecutive cycles.

Dynamics of epigenetic modifiers and environmentally sensitive proteins in a reptile with temperature induced sex reversal

The mechanisms by which sex is determined, and how a sexual phenotype is stably maintained during adulthood, has been the focus of vigorous scientific inquiry. Resources common to the biomedical field (automated staining and imaging platforms) were leveraged to provide the first immunofluorescent data for a reptile species with temperature induced sex reversal. Two four-plex immunofluorescent panels were explored across three sex classes (sex reversed ZZf females, normal ZWf females, and normal ZZm males). One panel was stained for chromatin remodelling genes JARID2 and KDM6B, and methylation marks H3K27me3, and H3K4me3 (Jumonji Panel). The other CaRe panel stained for environmental response genes CIRBP and RelA, and H3K27me3 and H3K4me3. Our study characterised tissue specific expression and cellular localisation patterns of these proteins and histone marks, providing new insights to the molecular characteristics of adult gonads in a dragon lizard Pogona vitticeps. The confirmation that mammalian antibodies cross react in P. vitticeps paves the way for experiments that can take advantage of this new immunohistochemical resource to gain a new understanding of the role of these proteins during embryonic development, and most importantly for P. vitticeps, the molecular underpinnings of sex reversal.

Histological study and immunohistochemical location of cytoskeletal proteins in the ovaries of the three species of lizards of the family Leiosauridae (Reptilia: Squamata)

The aim of the study is to expand information on the histological aspect, presence, and distribution of cytoskeletal proteins: smooth muscle alpha-actin (α-SMA), desmin and vimentin in ovaries of three lizards Leiosauridae. In all analysed species, the ovaries were paired organs, located inside the coelomic cavity, covered in a simple cubic epithelium. Below the surface was the tunica albuginea. The organs can be divided into two regions: the cortex and the medulla. The pre-vitellogenic follicles consist of an oocyte surrounded by the pellucid zone periodic acid schiff positive, the granulosa layer consisting of three cell types: small, intermediate, and large and the theca layer. The vitellogenic follicles presented only a single layer of cubic granulosa cells. In the three lizards, α-SMA microfilaments (MFs) were verified along the theca layer and in endothelial cells of the blood vessels of the analysed follicles. Researchers have observed desmin intermediate filaments immunostaining exclusively muscle fibers of the albuginea and the ovarian stroma of Enyalius perditus. There was no immunostaining for vimentin in the ovaries of all the lizards studied. Results obtained revealed that the MFs of α-SMA could be responsible for a contractile activity present in the lizards assessed.

Cytogenetic mechanisms of unisexuality in rock lizards

Darevskia rock lizards is a unique complex taxa, including more than thirty species, seven of which are parthenogenetic. In mixed populations of Darevskia lizards, tri- and tetraploid forms can be found. The most important issues in the theory of reticulate evolution of Darevskia lizards are the origin of parthenogenetic species and their taxonomic position. However, there is little data on how meiosis proceeds in these species. The present work reports the complex results of cytogenetics in a diploid parthenogenetic species – D. unisexualis. Here we detail the meiotic prophase I progression and the specific features оf mitotic chromosomes organization. The stages of meiosis prophase I were investigated by immunocytochemical analysis of preparations obtained from isolated primary oocytes of D. unisexualis in comparison with maternal species D. raddei nairensis. It has been shown that in D. unisexualis at the leptotene-zygotene stages the axial elements and the synaptonemal complex (SC) form typical “bouquets”. At the pachytene-diplotene stage, 18 autosomal SC-bivalents and thickened asynapted sex Z and w univalents were observed. The presence of SYCP1 protein between the lateral elements of autosomal chromosomes proved the formation of assembled SCs. Comparative genomic hybridization (CGH) on the mitotic metaphase chromosomes of D. unisexualis was carried out using the genomic DNA isolated from the parental species D. raddei nairensis and D. valentini. In the pericentromeric regions of half of the mitotic chromosomes of D. unisexualis, specific regions inherited from maternal species have been found. Following our results, we suggest a model for diploid germ cells formation from diploid oocytes without premeiotic duplication of chromosomes in the oogenesis of diploid parthenogenetic lizards D. unisexualis. Taken as a whole, our findings confirm the hybrid nature of D. unisexualis and shed light on heterozygosity and automixis in diploid parthenogenetic forms.