Biochemical analysis of actin in crane-fly gonial cells: evidence for actin in spermatocytes and spermatids--but not sperm.

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Abstract
A biochemical assay employing DNase-l affinity chromatography, 2-dimensional peptide analysis and [sodium dodecylsulfate] polyacrylamide gel electrophoresis was used to isolate, identify and assess the amount of actin from gonial cells of the crane fly, N. suturalis. Based on the analysis of cell homogenates under conditions in which all cellular actin is converted to the monomeric DNase-binding form, actin comprises .apprx. 1% of the total protein in homogenates of spermatocytes and spermatids. SDS gel analysis of mature sperm reveals no polypeptides with a MW similar to that of actin. Under conditions that preserve native supramolecular states of actin, .apprx. 80% of the spermatocyte actin is in a sedimentable form wheras only .apprx. 30% of the spermatid actin is sedimentable. These differences could be meaningful with regard to structural changes that occur during spermiogenesis. A comparative analysis of 2 dimensional peptide maps of several radioiodinated actins reveals similarities among spermatocyte, spermatid and human erythrocyte actins. The general applicability of this approach to other cell types that contain limited amounts of actin is suggested.