Expression of the Hsp23 chaperone during Drosophila embryogenesis: association to distinct neural and glial lineages.
BACKGROUND
In addition to their strong induction following stress, small heat shock proteins (Hsp) are also expressed during development in a wide variety of organisms. However, the precise identity of cell(s) expressing these proteins and the functional contribution of small heat shock proteins in such developmental context remain to be determined. The present study provides a detailed description of the Drosophila small heat shock protein Hsp23 expression pattern during embryogenesis and evaluates its functional contribution to central nervous system development.


RESULTS
Throughout embryogenesis, Hsp23 is expressed in a stage-specific manner by a restricted number of neuronal and glial lineages of the central nervous system. Hsp23 is also detected in the amnioserosa and within a single lateral chordotonal organ. Its expression within the MP2 lineage does not require the presence of a functional midline nor the activity of the Notch signaling pathway. Transactivation assays demonstrate that transcription factors implicated in the differentiation of the midline also regulate hsp23 promoter activity. Phenotypic analysis of a transgenic line exhibiting loss of Hsp23 expression in the central nervous system suggests that Hsp23 is not required for development and function of this tissue. Likewise, its overexpression does not cause deleterious effects, as development remains unaffected.


CONCLUSIONS
Based on the presented data, we suggest that the tightly regulated developmental expression of Hsp23 is not actively involved in cell differentiation and central nervous system development per se but rather reflects a putative role in preventive "pre-stress" neuroprotection or in non-vital process(es) common to the identified cell lineages.
Michaud
Sébastien
S
Laboratoire de Génétique Cellulaire et Développementale, Département de Médecine, Pavillon Marchand, Université Laval, Ste-Foy, Québec, Canada, G1K 7P4. smichau1@genetics.med.harvard.edu
Tanguay
Robert M
RM
D000818:Animals; D019070:Cell Lineage / Q000235:genetics / Q000502:physiology*; D018833:Chaperonins / Q000096:biosynthesis; D029721:Drosophila Proteins / Q000096:biosynthesis; D004331:Drosophila melanogaster / Q000196:embryology*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D006360:Heat-Shock Proteins / Q000096:biosynthesis*; D009420:Nervous System / Q000196:embryology; D009457:Neuroglia / Q000166:cytology* / Q000378:metabolism; D009474:Neurons / Q000166:cytology* / Q000378:metabolism
D029721:Drosophila Proteins; D006360:Heat-Shock Proteins; C105998:Hsp23 protein, Drosophila; D018833:Chaperonins