The adult cornea harbors stem cells (SCs) in its periphery, in a niche known as the limbus. Over the past 2 decades there has been substantial research into these adult corneal SCs, their limbal niche, and their therapeutic applications. However, few studies have investigated how this niche and its SCs develop in humans. To better characterize this development, human fetal corneas from 8.5-to 22-weeks'-gestation (n 5 173), neonatal (n 5 2), and adult (n 5 10) specimens were obtained. Histological and immunohistochemical assessments were conducted to determine embryological changes and expression of developmental and SC-related genes. Fresh fetal corneas were explanted to propagate corneal progenitors and cells characterized using reverse transcription-polymerase chain reaction, immunohistochemistry, flow cytometry, and colony-forming assays. A novel ''ridge-like'' structure was identified, circumscribing the fetal cornea, which we hypothesize represents the rudimentary SC niche. Immunohistochemistry disclosed ''stem-like'' cells across the cornea, becoming confined to this ridge with increasing gestational age. In addition, for the first time, pure longterm cultures of fetal corneal epithelium, which displayed phenotypical and functional properties similar to those of adult limbal SCs, were established. Optimization of culture techniques and purification of this SC population will allow for further investigation of their proliferative ability, with potential research and clinical applications. This study expands our understanding of limbal niche development and opens new avenues for investigation. STEM

Adult corneal stem cells (SCs) have been the subject of substantial research over the past 2 decades, with promising clinical applications being devised, refined, and tried. However, there have been few studies on the early development of these cells in humans, perhaps due to ethical and practical constraints. This review highlights work that has yielded significant insights from developmental studies in the cornea and other SC repositories. This field merits further research to improve our current knowledge of the origin of SCs, their location, phenotype, function, and niche structure, as well as providing fresh insight into the pathogenesis of congenital diseases and new therapeutic avenues for treating a range of blinding corneal diseases.

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The extent to which processing words involves breaking them down into smaller units or morphemes or is the result of an interactive activation of other units, such as meanings, letters, and sounds (e.g., dis-agree-ment vs. disagreement), is currently under debate. Disentangling morphology from phonology and semantics is often a methodological challenge, because orthogonal manipulations are difficult to achieve (e.g., semantically unrelated words are often phonologically related: casual-casualty and, vice versa, sign-signal). The present norms provide a morphological classification of 3,263 suffixed derived words from two widely spoken languages: English (2,204 words) and Spanish (1,059 words). Morphologically complex words were sorted into four categories according to the nature of their relationship with the base word: phonologically transparent (friend-friendly), phonologically opaque (child-children), semantically transparent (habit-habitual), and semantically opaque (event-eventual). In addition, ratings were gathered for age of acquisition, imageability, and semantic distance (i.e., the extent to which the meaning of the complex derived form could be drawn from the meaning of its base constituents). The norms were completed by adding values for word frequency; word length in number of phonemes, letters, and syllables; lexical similarity, as measured by the number of neighbors; and morphological family size. A series of comparative analyses from the collated ratings for the base and derived words were also carried out. The results are discussed in relation to recent findings.Keywords Age of acquisition . Morphology . Phonology . Semantics . English . SpanishThe phonological, orthographic, morphological, and semantic characteristics of words are central elements in word processing research. This is because finding out how the mind interacts with the structures of language (i.e., its sounds, its letters, its morphemes, and the meaning of its words) has proved to be a successful method of understanding the cognitive basis of language production and comprehension (Brysbaert, Van Wijnendaele, & De Deyne, 2000;Cattell, 1886;Davies, Barbón, & Cuetos, 2013;Duñabeitia, Laka, Perea, & Carreiras, 2009;Frederiksen & Kroll, 1976;Izura, Hernández-Muñoz, & Ellis, 2005;Lavidor & Ellis, 2002;Levelt, 1989;Macizo & Bajo, 2006;Marslen-Wilson, Tyler, Waksler, & Older, 1994;Pérez, 2007).Morphology, in particular, refers to the compositional structure that meaning has within the words in a language. Thus, words are often composed of smaller meaningful units called morphemes (e.g., home-work, penni-less, review-ed). Morphemes can both stand alone as monomorphemic words (e.g., truth) and be bonded to other morphemes as part of polymorphemic words (e.g., -ful in truthful). Morphologically complex words consist of a core morpheme, called root, base, or stem, and one or several add-on morphemes called affixes. In languages such as English and Spanish, affixes can be placed either at the beginning of the word (e.g., fore-in for...

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