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Advances in the spatiotemporal resolution and field-of-view of neuroimaging tools are driving mesoscale studies for translational neuroscience. On October 10, 2023, the Center for Mesoscale Mapping (CMM) at the Massachusetts General Hospital (MGH) Athinoula A. Martinos Center for Biomedical Imaging and the Massachusetts Institute of Technology (MIT) Health Sciences Technology based Neuroimaging Training Program (NTP) hosted a symposium exploring the state-of-the-art in this rapidly growing area of research. "Mesoscale Brain Mapping: Bridging Scales and Modalities in Neuroimaging" brought together researchers who use a broad range of imaging techniques to study brain structure and function at the convergence of the microscopic and macroscopic scales. The day-long event centered on areas in which the CMM has established expertise, including the development of emerging technologies and their application to clinical translational needs and basic neuroscience questions. The in-person symposium welcomed more than 150 attendees, including 57 faculty members, 61 postdoctoral fellows, 35 students, and four industry professionals, who represented institutions at the local, regional, and international levels. The symposium also served the training goals of both the CMM and the NTP. The event content, organization, and format were planned collaboratively by the faculty and trainees. Many CMM faculty presented or participated in a panel discussion, thus contributing to the dissemination of both the technologies they have developed under the auspices of the CMM and the findings they have obtained using those technologies. NTP trainees who benefited from the symposium included those who helped to organize the symposium and/or presented posters and gave "flash" oral presentations. In addition to gaining experience from presenting their work, they had opportunities throughout the day to engage in one-on-one discussions with visiting scientists and other faculty, potentially opening the door to future collaborations. The symposium presentations provided a deep exploration of the many technological advances enabling progress in structural and functional mesoscale brain imaging. Finally, students worked closely with the presenting faculty to develop this report summarizing the content of the symposium and putting it in the broader context of the current state of the field to share with the scientific community. We note that the references cited here include conference abstracts corresponding to the symposium poster presentations., (© 2024. The Author(s).)

The Person-Environment-Occupation-Performance (PEOP) Model is one of several occupation-based models in occupational therapy. The model describes the transactional nature of person, environment, and occupation factors that support performance (doing), participation (engagement), and well-being (health and quality of life). The purpose of this study was to explore the extent and nature of evidence on the PEOP Model. We used a scoping review to identify and analyze journal articles that used the PEOP Model as a framework for study. The PRISMA extension for scoping reviews (PRISMA-ScR) criteria were used to develop the research methods. We found 109 articles that adopted the PEOP Model as an organizing framework. The studies reviewed represent the breadth of occupational therapy practice and the transactional nature of person, environment, occupation, and performance in the PEOP Model. The PEOP Model is a useful international framework for research and practice across populations, conditions, life circumstances, settings, and areas of practice., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

In this study, we investigated the impact of various simulated skull bone geometries on the determination of skull speed of sound and acoustic attenuation values via optimization using transmitted pressure amplitudes beyond the bone. Using the hybrid angular spectrum method (HAS), we simulated ultrasound transmission through four model sets of different geometries involving sandwiched layers of diploë and cortical bone in addition to three models generated from CT images of ex-vivo human skull-bones. We characterized cost-function solution spaces for each model and, using optimization, found that when a model possessed appreciable variations in resolvable layer thickness, the predefined attenuation coefficients could be found with low error (RMSE < 0.01 Np/cm). However, we identified a spatial frequency cutoff in the models' geometry beyond which the accuracy of the property determination begins to fail, depending on the frequency of the ultrasound source. There was a large increase in error of the attenuation coefficients determined by the optimization when the variations in layer thickness were above the identified spatial frequency cutoffs, or when the lateral variations across the model were relatively low in amplitude. For our limited sample of three CT-image derived bone models, the attenuation coefficients were determined successfully. The speed of sound values were determined with low error for all models (including the CT-image derived models) that were tested (RMSE < 0.4 m/s). These results illustrate that it is possible to determine the acoustic properties of two-component models when the internal bone structure is taken into account and the structure satisfies the spatial frequency constraints discussed., (© 2023 John Wiley & Sons Ltd.)

Schistosomes are parasitic blood flukes that infect >200 million people around the world. Free-swimming larval stages penetrate the skin, invade a blood vessel, and migrate through the heart and lungs to the vasculature of the liver, where maturation and mating occurs. From here, the parasite couples migrate to their preferred egg laying sites. Here, we compare and contrast what is known about the migration patterns within the definitive host of the three major species of human schistosome: Schistosoma mansoni, S. japonicum, and S. haematobium. We conclude that intravascular schistosomes are inexorable colonizers whose migration and egg laying strategy is profligate; all three species (and their eggs) can be found throughout the mesenteric venules, the rectal venous plexus, and, to a greater or lesser extent, the urogenital venous plexuses. In addition, it is common for parasite eggs to be deposited in locations that lack easy access to the exterior, further demonstrating the relentless exploratory nature of these intravascular worms., Competing Interests: The authors have declared that no competing interests exist.

Purpose: The molecular mechanisms controlling aqueous humor (AQH) outflow and IOP need much further definition. The mouse is a powerful system for characterizing the mechanistic basis of AQH outflow. To enhance outflow studies in mice, we developed a perfusion system that is based on human anterior chamber perfusion culture systems. Our mouse system permits previously impractical experiments., Methods: We engineered a computer-controlled, pump-based perfusion system with a platform for mounting whole dissected mouse eyes (minus lens and iris, ∼45% of drainage tissue is perfused). We tested the system's ability to monitor outflow and tested the effects of the outflow-elevating drug, Y27632, a rho-associated protein kinase (ROCK) inhibitor. Finally, we tested the system's ability to detect genetically determined decreases in outflow by determining if deficiency of the candidate genes Nos3 and Cav1 alter outflow., Results: Using our system, the outflow facility (C) of C57BL/6J mouse eyes was found to range between 7.7 and 10.4 nl/minutes/mm Hg (corrected for whole eye). Our system readily detected a 74.4% Y27632-induced increase in C. The NOS3 inhibitor L-NG-nitroarginine methyl ester (L-NAME) and a Nos3 null mutation reduced C by 28.3% and 35.8%, respectively. Similarly, in Cav1 null eyes C was reduced by 47.8%., Conclusions: We engineered a unique perfusion system that can accurately measure changes in C. We then used the system to show that NOS3 and CAV1 are key components of mechanism(s) controlling outflow.

Introduction: The need for human cornea tissues continues to grow as an alternative option to donor tissues. Silk protein has been successfully used as a substrate to engineer corneal epithelium and stroma in vitro. Herein, we investigated the in vivo response and the effect of silk crystalline structure (beta sheet) on degradation rate of silk films in rabbit multipocket corneal models., Methods: Three different surgical techniques (peripheral-median P-M, central-superficial C-S, central-deep C-D) were used to assess the in vivo response as well as the degradation profile of silk films with low, medium and high beta sheet (crystalline) content at 2 and 3 months after surgery., Results: Approach C-D showed signs of sample degradation without inflammation, with one single incision and a pocket created by flushing air two thirds deep in the corneal stroma. In comparison, approaches P-M and C-S with multiple incisions presented manually dissected surgical pockets resulted in inflammation and possible extrusion of the samples, respectively. Low beta sheet samples lost structural integrity at 2 months after surgery C-D, while medium and high beta sheet content films showed initial evidence of degradation., Conclusions: The in vivo response to the silk films was dependent on the location of the implant and pocket depth. Crystallinity content in silk films played a significant role in the timing of material degradation, without signs of inflammation and vascularization or changes in stromal organization.

Purpose: Mutations in the gene encoding collagen type IV alpha 1 (COL4A1) cause multisystem disorders including anterior segment dysgenesis (ASD) and optic nerve hypoplasia. The penetrance and severity of individual phenotypes depends on genetic context. Here, we tested the effects of a Col4a1 mutation in two different genetic backgrounds to compare how genetic context influences ocular dysgenesis, IOP, and progression to glaucoma., Methods: Col4a1 mutant mice maintained on a C57BL/6J background were crossed to either 129S6/SvEvTac or CAST/EiJ and the F1 progeny were analyzed by slit-lamp biomicroscopy and optical coherence tomography. We also measured IOPs and compared tissue sections of eyes and optic nerves., Results: We found that the CAST/EiJ inbred strain has a relatively uniform and profound suppression on the effects of Col4a1 mutation and that mutant CASTB6F1 mice were generally only very mildly affected. In contrast, mutant 129B6F1 mice had more variable and severe ASD and IOP dysregulation that were associated with glaucomatous signs including lost or damaged retinal ganglion cell axons and excavation of the optic nerve head., Conclusions: Ocular defects in Col4a1 mutant mice model ASD and glaucoma that are observed in a subset of patients with COL4A1 mutations. We demonstrate that different inbred strains of mice give graded severities of ASD and we detected elevated IOP and glaucomatous damage in 129B6F1, but not CASTB6F1 mice that carried a Col4a1 mutation. These data demonstrate that genetic context differences are one factor that may contribute to the variable penetrance and severity of ASD and glaucoma in patients with COL4A1 mutations.

Schlemm's canal (SC) plays central roles in ocular physiology. These roles depend on the molecular phenotypes of SC endothelial cells (SECs). Both the specific phenotype of SECs and development of SC remain poorly defined. To allow a modern and extensive analysis of SC and its origins, we developed a new whole-mount procedure to visualize its development in the context of surrounding tissues. We then applied genetic lineage tracing, specific-fluorescent reporter genes, immunofluorescence, high-resolution confocal microscopy, and three-dimensional (3D) rendering to study SC. Using these techniques, we show that SECs have a unique phenotype that is a blend of both blood and lymphatic endothelial cell phenotypes. By analyzing whole mounts of postnatal mouse eyes progressively to adulthood, we show that SC develops from blood vessels through a newly discovered process that we name "canalogenesis." Functional inhibition of KDR (VEGFR2), a critical receptor in initiating angiogenesis, shows that this receptor is required during canalogenesis. Unlike angiogenesis and similar to stages of vasculogenesis, during canalogenesis tip cells divide and form branched chains prior to vessel formation. Differing from both angiogenesis and vasculogenesis, during canalogenesis SECs express Prox1, a master regulator of lymphangiogenesis and lymphatic phenotypes. Thus, SC development resembles a blend of vascular developmental programs. These advances define SC as a unique vessel with a combination of blood vascular and lymphatic phenotypes. They are important for dissecting its functions that are essential for ocular health and normal vision., Competing Interests: The authors have declared that no competing interests exist.

Glaucoma is one of the most common neurodegenerative diseases. Despite this, the earliest stages of this complex disease are still unclear. This study was specifically designed to identify early stages of glaucoma in DBA/2J mice. To do this, we used genome-wide expression profiling of optic nerve head and retina and a series of computational methods. Eyes with no detectable glaucoma by conventional assays were grouped into molecularly defined stages of disease using unbiased hierarchical clustering. These stages represent a temporally ordered sequence of glaucoma states. We then determined networks and biological processes that were altered at these early stages. Early-stage expression changes included upregulation of both the complement cascade and the endothelin system, and so we tested the therapeutic value of separately inhibiting them. Mice with a mutation in complement component 1a (C1qa) were protected from glaucoma. Similarly, inhibition of the endothelin system with bosentan, an endothelin receptor antagonist, was strongly protective against glaucomatous damage. Since endothelin 2 is potently vasoconstrictive and was produced by microglia/macrophages, our data provide what we believe to be a novel link between these cell types and vascular dysfunction in glaucoma. Targeting early molecular events, such as complement and endothelin induction, may provide effective new treatments for human glaucoma.

RGD-coupled silk protein-biomaterial lamellar systems were prepared and studied with human cornea fibroblasts (hCFs) to match functional requirements. A strategy for corneal tissue engineering was pursued to replicate the structural hierarchy of human corneal stroma within thin stacks of lamellae-like tissues, in this case constructed from scaffolds constructed with RGD-coupled, patterned, porous, mechanically robust and transparent silk films. The influence of RGD-coupling on the orientation, proliferation, ECM organization, and gene expression of hCFs was assessed. RGD surface modification enhanced cell attachment, proliferation, alignment and expression of both collagens (type I and V) and proteoglycans (decorin and biglycan). Confocal and histological images of the lamellar systems revealed that the bio-functionalized silk human cornea 3D constructs exhibited integrated corneal stroma tissue with helicoidal multi-lamellar alignment of collagen-rich and proteoglycan-rich extracellular matrix, with transparency of the construct. This biomimetic approach to replicate corneal stromal tissue structural hierarchy and architecture demonstrates a useful strategy for engineering human cornea. Further, this approach can be exploited for other tissue systems due to the pervasive nature of such helicoids in most human tissues., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Biomaterials for corneal tissue engineering must demonstrate several critical features for potential utility in vivo, including transparency, mechanical integrity, biocompatibility and slow biodegradation. Silk film biomaterials were designed and characterized to meet these functional requirements. Silk protein films were used in a biomimetic approach to replicate corneal stromal tissue architecture. The films were 2 microm thick to emulate corneal collagen lamellae dimensions, and were surface patterned to guide cell alignment. To enhance trans-lamellar diffusion of nutrients and to promote cell-cell interaction, pores with 0.5-5.0 microm diameters were introduced into the silk films. Human and rabbit corneal fibroblast proliferation, alignment and corneal extracellular matrix expression on these films in both 2D and 3D cultures were demonstrated. The mechanical properties, optical clarity and surface patterned features of these films, combined with their ability to support corneal cell functions suggest that this new biomaterial system offers important potential benefits for corneal tissue regeneration.

Here, we use a mouse model (DBA/2J) to readdress the location of insult(s) to retinal ganglion cells (RGCs) in glaucoma. We localize an early sign of axon damage to an astrocyte-rich region of the optic nerve just posterior to the retina, analogous to the lamina cribrosa. In this region, a network of astrocytes associates intimately with RGC axons. Using BAX-deficient DBA/2J mice, which retain all of their RGCs, we provide experimental evidence for an insult within or very close to the lamina in the optic nerve. We show that proximal axon segments attached to their cell bodies survive to the proximity of the lamina. In contrast, axon segments in the lamina and behind the eye degenerate. Finally, the Wld(s) allele, which is known to protect against insults to axons, strongly protects against DBA/2J glaucoma and preserves RGC activity as measured by pattern electroretinography. These experiments provide strong evidence for a local insult to axons in the optic nerve.

Background: The glaucomas are a common but incompletely understood group of diseases. DBA/2J mice develop a pigment liberating iris disease that ultimately causes elevated intraocular pressure (IOP) and glaucoma. We have shown previously that mutations in two genes, Gpnmb and Tyrp1, initiate the iris disease. However, mechanisms involved in the subsequent IOP elevation and optic nerve degeneration remain unclear., Results: Here we present new mouse strains with Gpnmb and/or Tyrp1 genes of normal function and with a DBA/2J genetic background. These strains do not develop elevated IOP or glaucoma with age., Conclusion: These strains provide much needed controls for studying pathogenic mechanisms of glaucoma using DBA/2J mice. Given the involvement of Gpnmb and/or Tyrp1 in areas such as immunology and tumor development and progression, these strains are also important in other research fields.

Ocular anterior segment dysgenesis (ASD) is a complex and poorly understood group of conditions. A large proportion of individuals with ASD develop glaucoma, a leading cause of blindness resulting from retinal ganglion cell death. Optic nerve hypoplasia is thought to have distinct causes and is a leading cause of blindness in children. Here, we show that a mutation in the type IV collagen alpha 1 (Col4a1) gene can cause both ASD and optic nerve hypoplasia. COL4A1 is a major component of almost all basement membranes. The mutation results in non-secretion of the mutant COL4A1 proteins, which instead accumulate within cells. Basement membrane abnormalities may, therefore, contribute to the phenotype. The mutation also induces endoplasmic reticulum stress and so intracellular stress may contribute to pathogenesis. The overall consequence of the Col4a1 mutation depends on genetic context. In one genetic context, the mutation causes severe ASD with intraocular pressure abnormalities and optic nerve hypoplasia. In a different genetic context, both the ASD and optic nerve hypoplasia are rescued, and we have identified a single dominant locus that confers the phenotypic modification.

The anterior avian cornea possesses several distinct cellular and extracellular regions including the epithelial basal lamina, Bowman's layer and the interfacial matrix that separates Bowman's layer from the stroma. These unique regions differ biochemically, physically and morphologically but all contain type XII collagen. Previously, the collagen fibrils of several of these interfacial regions were shown to be stable to thermal and enzymatic denaturation. We reasoned that type XII collagen, a fibril-associated collagen, would be a good candidate to confer such stabilizing properties. The studies described herein were performed to localize type XII collagen and to assess its role in the interfacial matrices (IM). Using antibodies that react with both the short and long type XII collagen isoforms and that react specifically with the long isoform, we demonstrate that it is the short isoform that is present in Bowman's layer and the associated interfacial matrix lying between Bowman's and the stroma proper. In situ hybridization analyses demonstrate that both the epithelial and endothelial cells synthesize type XII collagen. In vitro cell culture analyses, however, demonstrate that in addition to epithelial cell synthesis, the stromal fibroblasts are capable of synthesizing type XII collagen as well. Immunofluorescence analyses performed at elevated temperature demonstrate that type XII collagen is thermally stable in Bowman's layer, but not in the anterior interfacial matrix or Descemet's layer. In addition, we observed that the distribution of type XII collagen during the development of the anterior extracellular matrices correlates precisely with an elevated density of keratocytes populating the interfacial matrix just deep to Bowman's layer. We show that this cellular density is developmentally regulated and does not arise from a localized increase in cell proliferation. These data demonstrate that Bowman's layer and the anterior interfacial matrix have unique biochemical and morphologic properties. Type XII collagen is thermally stable in Bowman's layer and, as a surface component of type I collagen fibrils, may contribute to the stability of the fibrils in this region. Neither type XII nor type I collagen is stable in the adjacent interfacial matrix, suggesting that differences in the type I-XII collagen fibril organization may exist between Bowman's layer and IM.

Chicken alpha1(V) collagen cDNAs have been cloned by a variety of methods and positively identified. We present here the entire translated sequence of the chick polypeptide and compare selected regions to other collagen chains in the type V/XI family.

Corneal development requires the production, assembly and sometimes replacement of a number of collagenous matrices. The embryonic chick cornea is well-characterized and offers certain advantages for studying the assembly and roles of these matrices. We will first describe the matrices to be examined. These include the corneal stroma proper, first formed as the primary stroma and subsequently as the secondary (mature) stroma; Bowman's Membrane; Descemet's Membrane; and the hemidesmosome of the epithelial cell attachment complex. We will then describe the characteristics of the collagen types involved, including: the fibrillar collagens (types I, II and V), the fibril-associated collagens (types IX, XII and XIV), and the transmembrane collagen of the hemidesmosome (type XVII). Then, in each subsequent section we will examine in detail the structure, assembly and development of each collagenous matrix, and how each specific collagen and/or combination of collagens are thought to provide the matrices with their unique properties. The work and views presented here are largely from our own laboratories. Thus, this article is not meant to be a comprehensive review of the literature. For pertinent references by others, when possible, we will cite recent reviews.

A number of factors have been implicated in the regulation of tissue-specific collagen fibril diameter. Previous data suggest that assembly of heterotypic fibrils composed of two different fibrillar collagens represents a general mechanism regulating fibril diameter. Specifically, we hypothesize that type V collagen is required for the assembly of the small diameter fibrils observed in the cornea. To test this, we used a dominant-negative retroviral strategy to decrease the levels of type V collagen secreted by chicken corneal fibroblasts. The chicken alpha 1(V) collagen gene was cloned, and retroviral vectors that expressed a polycistronic mRNA encoding a truncated alpha 1(V) minigene and the reporter gene LacZ were constructed. The efficiency of viral infection was 30-40%, as determined by assaying beta-galactosidase activity. To assess the expression from the recombinant provirus, Northern analysis was performed and indicated that infected fibroblasts expressed high steady-state levels of retroviral mRNA. Infected cells synthesized the truncated alpha 1(V) protein, and this was detectable only intracellularly, in a distribution that colocalized with lysosomes. To assess endogenous alpha 1(V) protein levels, infected cell cultures were assayed, and these consistently demonstrated reductions relative to control virus-infected or uninfected cultures. Analyses of corneal fibril morphology demonstrated that the reduction in type V collagen resulted in the assembly of large-diameter fibrils with a broad size distribution, characteristics similar to fibrils produced in connective tissues with low type V concentrations. Immunoelectron microscopy demonstrated the amino-terminal domain of type V collagen was associated with the small-diameter fibrils, but not the large fibrils. These data indicate that type V collagen levels regulate corneal fibril diameter and that the reduction of type V collagen is sufficient to alter fibril assembly so that abnormally large-diameter fibrils are deposited into the matrix.

Corneal development involves the synthesis and assembly of a number of specialized extracellular matrices. These matrices have distinctive properties derived from a unique assembly of collagens, proteoglycans and glycoproteins. The synthesis of each of these requires a number of enzymes. By probing a corneal cDNA library for genes that appeared to be up-regulated in cornea we have isolated a cDNA that represents an mRNA encoding the enzyme beta-1,4-galactosyltransferase. In cornea, a major function for this enzyme is likely to be in the synthesis of the keratan sulfate proteoglycan, lumican. Employing quantitative reverse transcript-polymerase chain reaction, we have observed that the steady-state level of mRNA for the molecule is elevated during certain stages of corneal development. It is also elevated in corneal fibroblasts in culture that have a greatly decreased synthesis of the mature lumican molecule. These data are consistent with, and complement, studies by others that show a corresponding regulation of the lumican core protein during development and in corneal fibroblast cultures.

In order to investigate how the maternally specified animal-vegetal axis of the sea urchin embryo is established, we have examined the molecular basis of regulation of several genes transcribed differentially in nonvegetal and vegetal domains of the very early blastula. Here we present an initial characterization of the regulatory region of one of these, SpAN, which encodes a protease in the astacin family related to Drosophila tolloid and vertebrate BMP-1 (Reynolds et al., Development 114, 769-786). Tests of SpAN promoter function in vivo show that high-level activity and correct not-vegetal expression are mediated by sequences within 300 bp upstream of the basal promoter. In vitro studies have identified six protein binding sites serviced by at least five different proteins. Comparison of the structure of the SpAN promoter to that of SpHE, whose expression pattern is identical, shows that both promoters contain multiple positively acting upstream elements close to the basal promoter. We show that two elements are critical for high-level transcription of SpAN, since exact replacement of either results in 10- to 20-fold reduction in promoter strength. These shared elements are, however, not essential for spatially correct SpHE gene transcription. We conclude that the coordinate strong activities of the SpAN and SpHE promoters in the nonvegetal domain of the embryo rely primarily on different transcription factor activities.

In the development of chicken corneal stroma, two or more collagens often interact, either as constituents of a single heterotypic fibril or as components of the fibril surface. The latter, fibril-associated collagens, may facilitate interactions between fibrils and the surrounding extracellular matrix or between fibrils themselves. In an effort to isolate putative nonfibrillar collagens that may have such a function, we screened a 13-day embryonic cornea cDNA library under reduced stringency conditions, using a cDNA probe for a collagenous domain of type XII collagen. We isolated a 4.2-kilobase (kb) cDNA that predicts a "collagenous" protein that has three unusual, if not unique, features. (i) The putative polypeptide encoded by this cDNA has a structural arrangement in which numerous stretches of Gly-Xaa-Yaa triplets, typical of collagens, are interrupted by non-Gly-Xaa-Yaa regions. One of the potential triple-helical domains is 246 amino acids long, but most are much smaller, consisting of 15-36 amino acids. Many are very rich in the helix-stabilizing imino acid proline. (ii) Northern blot analyses demonstrated strong cDNA hybridization to a 6.8-kb mRNA whose expression is restricted to the cornea. No hybridization was observed to mRNAs from the nine other tissues used in these analyses, even with extended exposure of the film. (iii) The cDNA contains a short (less than or equal to 425-base-pair) sequence in the 3' untranslated region of the 6.8-kb mRNA that hybridizes to a 7.8-kb mRNA that has a wide tissue distribution.

To examine the regulation of collagen types IX and X during the hypertrophic phase of endochondral cartilage development, we have employed in situ hybridization and immunofluorescence histochemistry on selected stages of embryonic chick tibiotarsi. The data show that mRNA for type X collagen appears at or about the time that we detect the first appearance of the protein. This result is incompatible with translational regulation, which would require accumulation of the mRNA to occur at an appreciably earlier time. Data on later-stage embryos demonstrate that once hypertrophic chondrocytes initiate synthesis of type X collagen, they sustain high levels of its mRNA during the remainder of the hypertrophic program. This suggests that these cells maintain their integrity until close to the time that they are removed at the advancing marrow cavity. Type X collagen protein in the hypertrophic matrix also extends to the marrow cavity. Type IX collagen is found throughout the hypertrophic matrix, as well as throughout the younger cartilaginous matrices. But the mRNA for this molecule is largely or completely absent from the oldest hypertrophic cells. These data are consistent with a model that we have previously proposed in which newly synthesized type X collagen within the hypertrophic zone can become associated with type II/IX collagen fibrils synthesized and deposited earlier in development (Schmid and Linsenmayer, 1990; Chen et al. 1990).

In the embryonic avian eye, the vitreous and the primary corneal stroma are composed in part of collagen types II and IX. Previous biochemical and immunohistochemical studies have suggested that the production of these molecules changes dramatically during development. In the current investigation, we employed in situ hybridization to determine the temporospatial distribution of the messenger ribonucleic acids (mRNAs) for these collagens in the eyes of selected stages of chick embryos. Our observations suggest that through much of development, the ciliary region is the major source for the production of the collagens found within the vitreous. For the cornea, they confirm that both collagen mRNAs are indeed present, and suggest that each is independently regulated.