Embryology of the naso-palatal complex in Gekkota based on detailed 3D analysis in Lepidodactylus lugubris and Eublepharis macularius

Embryonic development of the skull in a parthenogenetic lizard, the mourning gecko (Lepidodactylus lugubris)

Gekkotans are one of the major clades of squamate reptiles. As one of the earliest-diverging lineages, they are crucial in studying deep-level squamate phylogeny and evolution. Developmental studies can shed light on the origin of many important morphological characters, yet our knowledge of cranial development in gekkotans is very incomplete. Here, we describe the embryonic development of the skull in a parthenogenetic gekkonid, the mourning gecko (Lepidodactylus lugubris), studied using non-acidic double staining and histological sectioning. Our analysis indicates that the pterygoid is the first ossifying bone in the skull, as in almost all other studied squamates, followed closely by the surangular and prearticular. The next to appear are the dentary, frontal, parietal and squamosal. The tooth-bearing upper jaw bones, the premaxilla and maxilla, develop relatively late. In contrast to previous reports, the premaxilla starts ossifying from two distinct centres, reminiscent of the condition observed in diplodactylids and eublepharids. Only a single ossification centre of the postorbitofrontal is observed. Some of the endochondral bones of the braincase (prootic, opisthotic, supraoccipital) and the dermal parasphenoid are the last bones to appear. The skull roof is relatively poorly ossified near the time of hatching, with a large frontoparietal fontanelle still present. Many bones begin ossifying relatively later in L. lugubris than in the phyllodactylid Tarentola annularis, which suggests that its ossification sequence is heterochronic with respect to T. annularis.

Ontogeny of the nasolacrimal apparatus and nasal sensory systems of the American alligator (Alligator mississippiensis)

The nasolacrimal apparatus (NLA) is a feature common to many sauropsid amniotes. It consists of an orbital Harderian gland (HG)whose secretions drain into the nasal cavity, in the vicinity of the vomeronasal organ (VNO), an accessory olfactory organ derived from the olfactory epithelium, and a connecting nasolacrimal duct (NLD). Though not all features are present in all posthatchling sauropsids (i.e., no VNO in crocodilomorphs), it is not clear if this system either never existed or failed to develop during the embryonic stages. The purpose of this study is to histologically describe the ontogeny of the NLA and the main olfactory organ in Alligator mississippiensis. Alligator specimens, from embryonic stage 9 to hatchling, were serially histologically sectioned, stained, photographed, and segmented into different tissues using Abobe Photoshop and then reconstructed using Amira for 3D analysis and quantitative nasal epithelial distribution. Though there was no evidence of a VNO, the rest of the NLA was present. The development of the NLA could be subdivided into four phases: (1) inception of NLD, (2) establishment of orbitonasal connections of NLD, (3) bone development, and (4) nasal cavity growth. Glands mature during this last phase and the nasal region rapidly grows, rotates, and is displaced anteriorly. The gradual proportional increase in nonolfactory epithelial distribution during ontogeny is consistent with the literature. Alligator embryonic nasal and NLD growth differs from that of mammals and squamates. The NLD is connected to the anterior third of the nasal region during its initial attachment, but as anterior nasal growth exceeds posterior growth, it is gradually displaced into the posterior third of the nasal region by hatching. It is unknown whether this is a derived archosaur condition or just another example of the morphological variation seen within sauropsid amniotes.

Changes in the avascular area of the meniscus using mesenchymal stem cells and growth plate chondrocytes in a pig model

Menisci are wedge-shaped cartilage discs that are divided into two parts: the avascular and vascular regions. They are formed by fibrocartilage tissue, which contains round cartilage-like cells and extracellular matrix. Meniscus injury in animals is a common orthopedic problem, but data on the natural healing process mainly deals with the vascular zone. The healing processes in the avascular zone of the meniscus are significantly limited. Thus, this study aimed to evaluate autologous growth plate chondrocytes' impact on the healing process of a damaged meniscus in the avascular zone based on a growing animal model. The study group consisted of 10 pigs at about three months of age. From each animal, chondrocytes from the iliac growth plate and from concentrated bone marrow were taken. Knee joints were divided into right (R) and left (L). The medial meniscus of the R knee joint was treated with a hyaluronic acid based scaffold incubated with bone marrow cells from marrow aspirates (nCHON). The medial meniscus of the L knee joint was treated with a hyaluronic acid based scaffold incubated with bone marrow cells from marrow aspirates supplemented with immature chondrocytes isolated from growth plates (wCHON). The meniscus was damaged in the avascular zone in both knee joints. Followingly, the damaged part of the meniscus was filled with a scaffold with cells from the concentrated bone marrow and from growth plate chondrocytes. In the control group, a scaffold with concentrated bone marrow cells was used. After three months the animals were euthanized and preparations (microscopic slides) were made from the meniscus' damaged part. A qualitative and quantitative analysis have been prepared. The wCHON group in comparison with the nCHON group showed a statistically significantly higher number of fusiform cells on the surface of the graft as well as better healing of the graft. In addition, the degree of vascularization was higher in specimens from the wCHON group than in the nCHON group. The results of our research on immature pig knees revealed that mesenchymal stem cell and growth plate chondrocytes could be treated as the cell source for meniscus reconstruction, and growth plate chondrocytes enhance healing processes in the avascular zone of the injured meniscus.

Architecture of the Pancreatic Islets and Endocrine Cell Arrangement in the Embryonic Pancreas of the Grass Snake (Natrix natrix L.). Immunocytochemical Studies and 3D Reconstructions

During the early developmental stages of grass snakes, within the differentiating pancreas, cords of endocrine cells are formed. They differentiate into agglomerates of large islets flanked throughout subsequent developmental stages by small groups of endocrine cells forming islets. The islets are located within the cephalic part of the dorsal pancreas. At the end of the embryonic period, the pancreatic islet agglomerates branch off, and as a result of their remodeling, surround the splenic "bulb". The stage of pancreatic endocrine ring formation is the first step in formation of intrasplenic islets characteristics for the adult specimens of the grass snake. The arrangement of endocrine cells within islets changes during pancreas differentiation. Initially, the core of islets formed from B and D cells is surrounded by a cluster of A cells. Subsequently, A, B, and D endocrine cells are mixed throughout the islets. Before grass snake hatching, A and B endocrine cells are intermingled within the islets, but D cells are arranged centrally. Moreover, the pancreatic polypeptide (PP) cells are not found within the embryonic pancreas of the grass snake. Variation in the proportions of different cell types, depending on the part of the pancreas, may affect the islet function-a higher proportion of glucagon cells is beneficial for insulin secretion.

Embryonic development and perinatal skeleton in a limbless, viviparous lizard, Anguis fragilis (Squamata: Anguimorpha)

Despite the long history of embryological studies of squamates, many groups of this huge clade have received only limited attention. One such understudied group is the anguimorphs, a clade comprising morphologically and ecologically very diverse lizards. We describe several stages of embryonic development of Anguis fragilis, a limbless, viviparous anguimorph. Interestingly, in several clutches we observe high morphological variation in characters traditionally important in classifying embryos into developmental stages. The causes of this variation remain unknown but environmental factors do not seem to be very important. Additionally, we describe the state of ossification in several perinatal specimens of A. fragilis. The cranial skeleton is relatively poorly ossified around the time of birth, with all of the bones constituting the braincase unfused. On the other hand, the vertebral column is well ossified, with the neurocentral sutures closed and the neural arches fused in all postatlantal vertebrae. Such an advanced state of ossification may be related to the greater importance of the vertebral column in locomotion in limbless species than in ones with fully-developed limbs. Numerous factors seem to affect the state of ossification at the time of hatching or birth in squamates, including phylogenetic position, mode of reproduction and, potentially, limblessness. However, data from a greater number of species are needed to reach firmer conclusions about the relative importance of these variables in certain clades.