Development of the nasolacrimal apparatus in the Mongolian gerbil (Meriones unguiculatus), with notes on network topology and function

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.

Morphological evaluation of the orbit, eye tunics, eyelids, and orbital glands in young and adult aardvarks Orycteropus afer, Pallas, 1766 (Tubulidentata: Orycteropodidae) - similarities and differences with representatives of the Afrotheria clade

The Afrotheria clade includes a large group of extant mammals, and the aardvark (Orycteropus afer) is the only representative of the order Tubulidentata in it. Here, we studied the morphological nature of the orbital region, eye tunics, upper and lower eyelids, superficial gland of the third eyelid, the third eyelid, deep gland of the third eyelid, and lacrimal gland in post-mortem specimens obtained from three captive aardvarks, two young and one adult. The obtained samples were analyzed using macroscopic, histological, and histochemical methods. We observed choroidal tapetum lucidum fibrosum in all specimens, which was typical for aardvarks. The superficial gland of the third eyelid was a compound multilobar tubular branched gland of a mucous nature. The deep gland of the third eyelid produced a serous secretion. The seromucous secretion was typical for the lacrimal gland. We compared the morphological data of the O. afer skull with that from other endemic African mammals in the Afrotheria clade. We found that other authors provided different anatomical names for some bones and foramina located within the orbit. The types and function of eyelid glands, as well as eyeball glands of aardvarks, can primarily be connected with their habitat. Our study may constitute an introduction to the ontogenesis of individual eyeball glands in aardvarks. This article is protected by copyright. All rights reserved.

Malformation of Tear Ducts Underlies the Epiphora and Precocious Eyelid Opening in Prickle 1 Mutant Mice: Genetic Implications for Tear Duct Genesis

Purpose

Obstruction of the tear drainage causes a range of ocular surface disorders. Hitherto, the genetics of tear duct development and obstruction has been scarcely explored, and related animal models are lacking. This study aims to study the potential role of the Wnt/PCP pathway mediated by Prickle 1 in tear duct development and diseases.

Methods

A severe hypomorphic Prickle 1 mutant was generated. Histology and immunohistochemistry were performed to compare wild type, Prickle 1 hypomorphic, and null mutant tear ducts. In situ hybridization was conducted to identify the signaling components in the developing tear ducts. Three-dimensional (3D) reconstruction was used to detect the human embryonic tear duct.

Results

Here, we report that a severe Prickle 1 hypomorph mouse line exhibited epiphora. This phenotype was due to the blockage of the tear drainage by incompletely formed nasolacrimal duct (NLD) and lacrimal canaliculi (LC), which also causes precocious eyelid opening. We observed a dose-dependent requirement of Prickle 1 for tear duct outgrowth. An investigation of the expression of Wnt/PCP core genes demonstrated a subset of PCP signaling components expressed in the developing tear duct. Furthermore, Prickle 1 is not required for the expression of Fgfr2/Fgf10 and p63 genes, which are associated with the NLD and LC hypoplasia in humans. Last, we showed that Prickle 1 expression in the developing tear drainage system is conserved between mice and humans.

Conclusions

The study suggests that malformed tear ducts caused by disruption of Prickle 1 underlies the epiphora and precocious eyelid opening.

Ontogenesis of the tear drainage system requires Prickle1-driven polarized basement membrane deposition

In terrestrial animals, the lacrimal drainage apparatus evolved to serve as conduits for tear flow; however, little is known about the ontogenesis of this system. Here, we define the anatomy of the fully formed tear duct in mice, characterize crucial morphogenetic events for the development of tear duct components and identify the site for primordial tear duct (PTD) initiation. We report that the PTD originates from the orbital lacrimal lamina, a junction formed by the epithelia of the maxillary and lateral nasal processes. We demonstrate that Prickle1, a key component of planar cell polarity signaling, is expressed in progenitors of the PTD and throughout tear duct morphogenesis. Disruption of Prickle1 stalls tear duct elongation; in particular, the loss of basement membrane deposition and aberrant cytoplasmic accumulation of laminin are salient. Altered cell adhesion, cytoskeletal transport systems, vesicular transport systems and cell axis orientation in Prickle1 mutants support the role of Prickle1 in planar cell polarity. Taken together, our results highlight a crucial role of Prickle1-mediated polarized basement membrane secretion and deposition in PTD elongation.

Ontogeny of the Orbital Glands and Their Environs in the Pantropical Spotted Dolphin (Stenella attenuata: Delphinidae)

The nasolacrimal duct (NLD) connects the orbital (often associated with the Deep Anterior Orbital gland: DAOG, a.k.a. Harderian gland) and nasal regions in many tetrapods. Adult cetaceans are usually said to lack an NLD, and there is little agreement in the literature concerning the identity of their orbital glands, which may reflect conflicting definitions rather than taxonomic variation. In this study, we examined an embryological series of the pantropical spotted dolphin (Stenella attenuata), and report numerous divergences from other tetrapods. Underdeveloped eyelids and a few ventral orbital glands are present by late Stage (S) 17. By S 19, circumorbital conjunctival glands are present. In S 20, these conjunctival glands have proliferated, eyelids (and scattered palpebral glands) have formed, and a duct similar to the NLD has appeared. Subsequently, both the palpebral glands and the NLD are progressively reduced by S 22, even as the conjunctival glands exhibit regional growth. In most tetrapods examined, the ontogeny of the NLD follows a series of three stages: Inception of NLD, Connection of orbit and nasal cavity by the NLD and Ossification (i.e., formation of the bony canal surrounding the NLD, emerging into the orbit via the lacrimal foramen in the lacrimal bone). In contrast, the dolphin NLD originates at the same time as the lacrimal bone, and a lacrimal foramen fails to develop. The cetacean fossil record shows that a lacrimal foramen was present in the earliest ancestral amphibious, freshwater forms, but was soon lost as the lineage invaded the oceans. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:77-87, 2018. © 2017 Wiley Periodicals, Inc.