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First published online 18 January 2006
doi: 10.1242/dev.02225

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XHas2 activity is required during somitogenesis and precursor cell migration in Xenopus development

¹ Laboratori di Biologia Cellulare e dello Sviluppo, Dipartimento di Fisiologia e Biochimica, Università di Pisa, Via Carducci 13, Ghezzano, Pisa (PI) 56010, Italy.
² Dipartimento di Biologia Evolutiva e Funzionale, Università di Parma, Viale delle Scienze 11/A Parma, (PR) 43100, Italy.
³ Divisione di Oncologia Sperimentale 2, Istituto Nazionale dei Tumori Aviano, CRO-IRCCS, Via Pedemontana Occidentale, 12, Aviano (PN) 33081, Italy.

^* Author for correspondence (e-mail: inardi{at}dfb.unipi.it)

Accepted 28 November 2005

In vertebrates, hyaluronan biosynthesis is regulated by three transmembrane catalytic enzymes denoted Has1, Has2 and Has3. We have previously cloned the Xenopus orthologues of the corresponding genes and defined their spatiotemporal distribution during development. During mammalian embryogenesis, Has2 activity is known to be crucial, as its abrogation in mice leads to early embryonic lethality. Here, we show that, in Xenopus, morpholino-mediated loss-of-function of XHas2 alters somitogenesis by causing a disruption of the metameric somitic pattern and leads to a defective myogenesis. In the absence of XHas2, early myoblasts underwent apoptosis, failing to complete their muscle differentiation programme. XHas2 activity is also required for migration of hypaxial muscle cells and trunk neural crest cells (NCC). To approach the mechanism whereby loss of HA, following XHas2 knockdown, could influence somitogenesis and precursor cell migration, we cloned the orthologue of the primary HA signalling receptor CD44 and addressed its function through an analogous knockdown approach. Loss of XCD44 did not disturb somitogenesis, but strongly impaired hypaxial muscle precursor cell migration and the subsequent formation of the ventral body wall musculature. In contrast to XHas2, loss of function of XCD44 did not seem to be essential for trunk NCC migration, suggesting that the HA dependence of NCC movement was rather associated with an altered macromolecular composition of the ECM structuring the cells' migratory pathways. The presented results, extend our knowledge on Has2 function and, for the first time, demonstrate a developmental role for CD44 in vertebrates. On the whole, these data underlie and confirm the emerging importance of cell-ECM interactions and modulation during embryonic development.

Key words: Has2, CD44, Hyaluronan, Somitogenesis, Myogenesis, Cell migration, Neural crest, ECM, Xenopus

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